GVN.cpp revision 244d24597497c09ab68969c8bbbdf2576130262c
1116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch//===- GVN.cpp - Eliminate redundant values and loads ---------------------===// 2116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// 3116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// The LLVM Compiler Infrastructure 4116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// 5116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// This file is distributed under the University of Illinois Open Source 6116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// License. See LICENSE.TXT for details. 7116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// 8116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch//===----------------------------------------------------------------------===// 9116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// 10116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// This pass performs global value numbering to eliminate fully redundant 11116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// instructions. It also performs simple dead load elimination. 12116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// 13116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// Note that this pass does the value numbering itself; it does not use the 14116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// ValueNumbering analysis passes. 15116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// 16116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch//===----------------------------------------------------------------------===// 17116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 18116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#define DEBUG_TYPE "gvn" 19116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Transforms/Scalar.h" 20116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/ADT/DenseMap.h" 21116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/ADT/DepthFirstIterator.h" 22116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/ADT/Hashing.h" 23116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/ADT/SmallPtrSet.h" 24116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/ADT/SetVector.h" 25116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/ADT/Statistic.h" 26116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/AliasAnalysis.h" 27116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/CFG.h" 28116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/ConstantFolding.h" 29116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/Dominators.h" 30116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/InstructionSimplify.h" 31116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/Loads.h" 32116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/MemoryBuiltins.h" 33116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/MemoryDependenceAnalysis.h" 34116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/PHITransAddr.h" 35116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Analysis/ValueTracking.h" 36116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Assembly/Writer.h" 37116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/IR/DataLayout.h" 38116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/IR/GlobalVariable.h" 39116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/IR/IRBuilder.h" 40116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/IR/IntrinsicInst.h" 41116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/IR/LLVMContext.h" 42116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/IR/Metadata.h" 43116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Support/Allocator.h" 44116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Support/CommandLine.h" 45116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Support/Debug.h" 46116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Support/PatternMatch.h" 47116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Target/TargetLibraryInfo.h" 48116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Transforms/Utils/BasicBlockUtils.h" 49116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include "llvm/Transforms/Utils/SSAUpdater.h" 50116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch#include <vector> 51116680a4aac90f2aa7413d9095a592090648e557Ben Murdochusing namespace llvm; 52116680a4aac90f2aa7413d9095a592090648e557Ben Murdochusing namespace PatternMatch; 53116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 54116680a4aac90f2aa7413d9095a592090648e557Ben MurdochSTATISTIC(NumGVNInstr, "Number of instructions deleted"); 55116680a4aac90f2aa7413d9095a592090648e557Ben MurdochSTATISTIC(NumGVNLoad, "Number of loads deleted"); 56116680a4aac90f2aa7413d9095a592090648e557Ben MurdochSTATISTIC(NumGVNPRE, "Number of instructions PRE'd"); 57116680a4aac90f2aa7413d9095a592090648e557Ben MurdochSTATISTIC(NumGVNBlocks, "Number of blocks merged"); 58116680a4aac90f2aa7413d9095a592090648e557Ben MurdochSTATISTIC(NumGVNSimpl, "Number of instructions simplified"); 59116680a4aac90f2aa7413d9095a592090648e557Ben MurdochSTATISTIC(NumGVNEqProp, "Number of equalities propagated"); 60116680a4aac90f2aa7413d9095a592090648e557Ben MurdochSTATISTIC(NumPRELoad, "Number of loads PRE'd"); 61116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 62116680a4aac90f2aa7413d9095a592090648e557Ben Murdochstatic cl::opt<bool> EnablePRE("enable-pre", 63116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch cl::init(true), cl::Hidden); 64116680a4aac90f2aa7413d9095a592090648e557Ben Murdochstatic cl::opt<bool> EnableLoadPRE("enable-load-pre", cl::init(true)); 65116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 66116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// Maximum allowed recursion depth. 67116680a4aac90f2aa7413d9095a592090648e557Ben Murdochstatic cl::opt<uint32_t> 68116680a4aac90f2aa7413d9095a592090648e557Ben MurdochMaxRecurseDepth("max-recurse-depth", cl::Hidden, cl::init(1000), cl::ZeroOrMore, 69116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch cl::desc("Max recurse depth (default = 1000)")); 70116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 71116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch//===----------------------------------------------------------------------===// 72116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch// ValueTable Class 73116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch//===----------------------------------------------------------------------===// 74116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 75116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch/// This class holds the mapping between values and value numbers. It is used 76116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch/// as an efficient mechanism to determine the expression-wise equivalence of 77116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch/// two values. 78116680a4aac90f2aa7413d9095a592090648e557Ben Murdochnamespace { 79116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch struct Expression { 80116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch uint32_t opcode; 81116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch Type *type; 82116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch SmallVector<uint32_t, 4> varargs; 83116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 84116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch Expression(uint32_t o = ~2U) : opcode(o) { } 85116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 86116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch bool operator==(const Expression &other) const { 87116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch if (opcode != other.opcode) 88116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch return false; 89116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch if (opcode == ~0U || opcode == ~1U) 90116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch return true; 91116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch if (type != other.type) 92116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch return false; 93116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch if (varargs != other.varargs) 94116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch return false; 95116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch return true; 96116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch } 97116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 98116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch friend hash_code hash_value(const Expression &Value) { 99116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch return hash_combine(Value.opcode, Value.type, 100116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch hash_combine_range(Value.varargs.begin(), 101116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch Value.varargs.end())); 102116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch } 103116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch }; 104116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 105116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch class ValueTable { 106116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch DenseMap<Value*, uint32_t> valueNumbering; 107116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch DenseMap<Expression, uint32_t> expressionNumbering; 108116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch AliasAnalysis *AA; 109116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch MemoryDependenceAnalysis *MD; 110116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch DominatorTree *DT; 111116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 112116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch uint32_t nextValueNumber; 113116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch 114116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch Expression create_expression(Instruction* I); 115116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch Expression create_cmp_expression(unsigned Opcode, 116116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch CmpInst::Predicate Predicate, 117116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch Value *LHS, Value *RHS); 118116680a4aac90f2aa7413d9095a592090648e557Ben Murdoch Expression create_extractvalue_expression(ExtractValueInst* EI); 119 uint32_t lookup_or_add_call(CallInst* C); 120 public: 121 ValueTable() : nextValueNumber(1) { } 122 uint32_t lookup_or_add(Value *V); 123 uint32_t lookup(Value *V) const; 124 uint32_t lookup_or_add_cmp(unsigned Opcode, CmpInst::Predicate Pred, 125 Value *LHS, Value *RHS); 126 void add(Value *V, uint32_t num); 127 void clear(); 128 void erase(Value *v); 129 void setAliasAnalysis(AliasAnalysis* A) { AA = A; } 130 AliasAnalysis *getAliasAnalysis() const { return AA; } 131 void setMemDep(MemoryDependenceAnalysis* M) { MD = M; } 132 void setDomTree(DominatorTree* D) { DT = D; } 133 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 134 void verifyRemoved(const Value *) const; 135 }; 136} 137 138namespace llvm { 139template <> struct DenseMapInfo<Expression> { 140 static inline Expression getEmptyKey() { 141 return ~0U; 142 } 143 144 static inline Expression getTombstoneKey() { 145 return ~1U; 146 } 147 148 static unsigned getHashValue(const Expression e) { 149 using llvm::hash_value; 150 return static_cast<unsigned>(hash_value(e)); 151 } 152 static bool isEqual(const Expression &LHS, const Expression &RHS) { 153 return LHS == RHS; 154 } 155}; 156 157} 158 159//===----------------------------------------------------------------------===// 160// ValueTable Internal Functions 161//===----------------------------------------------------------------------===// 162 163Expression ValueTable::create_expression(Instruction *I) { 164 Expression e; 165 e.type = I->getType(); 166 e.opcode = I->getOpcode(); 167 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end(); 168 OI != OE; ++OI) 169 e.varargs.push_back(lookup_or_add(*OI)); 170 if (I->isCommutative()) { 171 // Ensure that commutative instructions that only differ by a permutation 172 // of their operands get the same value number by sorting the operand value 173 // numbers. Since all commutative instructions have two operands it is more 174 // efficient to sort by hand rather than using, say, std::sort. 175 assert(I->getNumOperands() == 2 && "Unsupported commutative instruction!"); 176 if (e.varargs[0] > e.varargs[1]) 177 std::swap(e.varargs[0], e.varargs[1]); 178 } 179 180 if (CmpInst *C = dyn_cast<CmpInst>(I)) { 181 // Sort the operand value numbers so x<y and y>x get the same value number. 182 CmpInst::Predicate Predicate = C->getPredicate(); 183 if (e.varargs[0] > e.varargs[1]) { 184 std::swap(e.varargs[0], e.varargs[1]); 185 Predicate = CmpInst::getSwappedPredicate(Predicate); 186 } 187 e.opcode = (C->getOpcode() << 8) | Predicate; 188 } else if (InsertValueInst *E = dyn_cast<InsertValueInst>(I)) { 189 for (InsertValueInst::idx_iterator II = E->idx_begin(), IE = E->idx_end(); 190 II != IE; ++II) 191 e.varargs.push_back(*II); 192 } 193 194 return e; 195} 196 197Expression ValueTable::create_cmp_expression(unsigned Opcode, 198 CmpInst::Predicate Predicate, 199 Value *LHS, Value *RHS) { 200 assert((Opcode == Instruction::ICmp || Opcode == Instruction::FCmp) && 201 "Not a comparison!"); 202 Expression e; 203 e.type = CmpInst::makeCmpResultType(LHS->getType()); 204 e.varargs.push_back(lookup_or_add(LHS)); 205 e.varargs.push_back(lookup_or_add(RHS)); 206 207 // Sort the operand value numbers so x<y and y>x get the same value number. 208 if (e.varargs[0] > e.varargs[1]) { 209 std::swap(e.varargs[0], e.varargs[1]); 210 Predicate = CmpInst::getSwappedPredicate(Predicate); 211 } 212 e.opcode = (Opcode << 8) | Predicate; 213 return e; 214} 215 216Expression ValueTable::create_extractvalue_expression(ExtractValueInst *EI) { 217 assert(EI != 0 && "Not an ExtractValueInst?"); 218 Expression e; 219 e.type = EI->getType(); 220 e.opcode = 0; 221 222 IntrinsicInst *I = dyn_cast<IntrinsicInst>(EI->getAggregateOperand()); 223 if (I != 0 && EI->getNumIndices() == 1 && *EI->idx_begin() == 0 ) { 224 // EI might be an extract from one of our recognised intrinsics. If it 225 // is we'll synthesize a semantically equivalent expression instead on 226 // an extract value expression. 227 switch (I->getIntrinsicID()) { 228 case Intrinsic::sadd_with_overflow: 229 case Intrinsic::uadd_with_overflow: 230 e.opcode = Instruction::Add; 231 break; 232 case Intrinsic::ssub_with_overflow: 233 case Intrinsic::usub_with_overflow: 234 e.opcode = Instruction::Sub; 235 break; 236 case Intrinsic::smul_with_overflow: 237 case Intrinsic::umul_with_overflow: 238 e.opcode = Instruction::Mul; 239 break; 240 default: 241 break; 242 } 243 244 if (e.opcode != 0) { 245 // Intrinsic recognized. Grab its args to finish building the expression. 246 assert(I->getNumArgOperands() == 2 && 247 "Expect two args for recognised intrinsics."); 248 e.varargs.push_back(lookup_or_add(I->getArgOperand(0))); 249 e.varargs.push_back(lookup_or_add(I->getArgOperand(1))); 250 return e; 251 } 252 } 253 254 // Not a recognised intrinsic. Fall back to producing an extract value 255 // expression. 256 e.opcode = EI->getOpcode(); 257 for (Instruction::op_iterator OI = EI->op_begin(), OE = EI->op_end(); 258 OI != OE; ++OI) 259 e.varargs.push_back(lookup_or_add(*OI)); 260 261 for (ExtractValueInst::idx_iterator II = EI->idx_begin(), IE = EI->idx_end(); 262 II != IE; ++II) 263 e.varargs.push_back(*II); 264 265 return e; 266} 267 268//===----------------------------------------------------------------------===// 269// ValueTable External Functions 270//===----------------------------------------------------------------------===// 271 272/// add - Insert a value into the table with a specified value number. 273void ValueTable::add(Value *V, uint32_t num) { 274 valueNumbering.insert(std::make_pair(V, num)); 275} 276 277uint32_t ValueTable::lookup_or_add_call(CallInst *C) { 278 if (AA->doesNotAccessMemory(C)) { 279 Expression exp = create_expression(C); 280 uint32_t &e = expressionNumbering[exp]; 281 if (!e) e = nextValueNumber++; 282 valueNumbering[C] = e; 283 return e; 284 } else if (AA->onlyReadsMemory(C)) { 285 Expression exp = create_expression(C); 286 uint32_t &e = expressionNumbering[exp]; 287 if (!e) { 288 e = nextValueNumber++; 289 valueNumbering[C] = e; 290 return e; 291 } 292 if (!MD) { 293 e = nextValueNumber++; 294 valueNumbering[C] = e; 295 return e; 296 } 297 298 MemDepResult local_dep = MD->getDependency(C); 299 300 if (!local_dep.isDef() && !local_dep.isNonLocal()) { 301 valueNumbering[C] = nextValueNumber; 302 return nextValueNumber++; 303 } 304 305 if (local_dep.isDef()) { 306 CallInst* local_cdep = cast<CallInst>(local_dep.getInst()); 307 308 if (local_cdep->getNumArgOperands() != C->getNumArgOperands()) { 309 valueNumbering[C] = nextValueNumber; 310 return nextValueNumber++; 311 } 312 313 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 314 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 315 uint32_t cd_vn = lookup_or_add(local_cdep->getArgOperand(i)); 316 if (c_vn != cd_vn) { 317 valueNumbering[C] = nextValueNumber; 318 return nextValueNumber++; 319 } 320 } 321 322 uint32_t v = lookup_or_add(local_cdep); 323 valueNumbering[C] = v; 324 return v; 325 } 326 327 // Non-local case. 328 const MemoryDependenceAnalysis::NonLocalDepInfo &deps = 329 MD->getNonLocalCallDependency(CallSite(C)); 330 // FIXME: Move the checking logic to MemDep! 331 CallInst* cdep = 0; 332 333 // Check to see if we have a single dominating call instruction that is 334 // identical to C. 335 for (unsigned i = 0, e = deps.size(); i != e; ++i) { 336 const NonLocalDepEntry *I = &deps[i]; 337 if (I->getResult().isNonLocal()) 338 continue; 339 340 // We don't handle non-definitions. If we already have a call, reject 341 // instruction dependencies. 342 if (!I->getResult().isDef() || cdep != 0) { 343 cdep = 0; 344 break; 345 } 346 347 CallInst *NonLocalDepCall = dyn_cast<CallInst>(I->getResult().getInst()); 348 // FIXME: All duplicated with non-local case. 349 if (NonLocalDepCall && DT->properlyDominates(I->getBB(), C->getParent())){ 350 cdep = NonLocalDepCall; 351 continue; 352 } 353 354 cdep = 0; 355 break; 356 } 357 358 if (!cdep) { 359 valueNumbering[C] = nextValueNumber; 360 return nextValueNumber++; 361 } 362 363 if (cdep->getNumArgOperands() != C->getNumArgOperands()) { 364 valueNumbering[C] = nextValueNumber; 365 return nextValueNumber++; 366 } 367 for (unsigned i = 0, e = C->getNumArgOperands(); i < e; ++i) { 368 uint32_t c_vn = lookup_or_add(C->getArgOperand(i)); 369 uint32_t cd_vn = lookup_or_add(cdep->getArgOperand(i)); 370 if (c_vn != cd_vn) { 371 valueNumbering[C] = nextValueNumber; 372 return nextValueNumber++; 373 } 374 } 375 376 uint32_t v = lookup_or_add(cdep); 377 valueNumbering[C] = v; 378 return v; 379 380 } else { 381 valueNumbering[C] = nextValueNumber; 382 return nextValueNumber++; 383 } 384} 385 386/// lookup_or_add - Returns the value number for the specified value, assigning 387/// it a new number if it did not have one before. 388uint32_t ValueTable::lookup_or_add(Value *V) { 389 DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V); 390 if (VI != valueNumbering.end()) 391 return VI->second; 392 393 if (!isa<Instruction>(V)) { 394 valueNumbering[V] = nextValueNumber; 395 return nextValueNumber++; 396 } 397 398 Instruction* I = cast<Instruction>(V); 399 Expression exp; 400 switch (I->getOpcode()) { 401 case Instruction::Call: 402 return lookup_or_add_call(cast<CallInst>(I)); 403 case Instruction::Add: 404 case Instruction::FAdd: 405 case Instruction::Sub: 406 case Instruction::FSub: 407 case Instruction::Mul: 408 case Instruction::FMul: 409 case Instruction::UDiv: 410 case Instruction::SDiv: 411 case Instruction::FDiv: 412 case Instruction::URem: 413 case Instruction::SRem: 414 case Instruction::FRem: 415 case Instruction::Shl: 416 case Instruction::LShr: 417 case Instruction::AShr: 418 case Instruction::And: 419 case Instruction::Or: 420 case Instruction::Xor: 421 case Instruction::ICmp: 422 case Instruction::FCmp: 423 case Instruction::Trunc: 424 case Instruction::ZExt: 425 case Instruction::SExt: 426 case Instruction::FPToUI: 427 case Instruction::FPToSI: 428 case Instruction::UIToFP: 429 case Instruction::SIToFP: 430 case Instruction::FPTrunc: 431 case Instruction::FPExt: 432 case Instruction::PtrToInt: 433 case Instruction::IntToPtr: 434 case Instruction::BitCast: 435 case Instruction::Select: 436 case Instruction::ExtractElement: 437 case Instruction::InsertElement: 438 case Instruction::ShuffleVector: 439 case Instruction::InsertValue: 440 case Instruction::GetElementPtr: 441 exp = create_expression(I); 442 break; 443 case Instruction::ExtractValue: 444 exp = create_extractvalue_expression(cast<ExtractValueInst>(I)); 445 break; 446 default: 447 valueNumbering[V] = nextValueNumber; 448 return nextValueNumber++; 449 } 450 451 uint32_t& e = expressionNumbering[exp]; 452 if (!e) e = nextValueNumber++; 453 valueNumbering[V] = e; 454 return e; 455} 456 457/// lookup - Returns the value number of the specified value. Fails if 458/// the value has not yet been numbered. 459uint32_t ValueTable::lookup(Value *V) const { 460 DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V); 461 assert(VI != valueNumbering.end() && "Value not numbered?"); 462 return VI->second; 463} 464 465/// lookup_or_add_cmp - Returns the value number of the given comparison, 466/// assigning it a new number if it did not have one before. Useful when 467/// we deduced the result of a comparison, but don't immediately have an 468/// instruction realizing that comparison to hand. 469uint32_t ValueTable::lookup_or_add_cmp(unsigned Opcode, 470 CmpInst::Predicate Predicate, 471 Value *LHS, Value *RHS) { 472 Expression exp = create_cmp_expression(Opcode, Predicate, LHS, RHS); 473 uint32_t& e = expressionNumbering[exp]; 474 if (!e) e = nextValueNumber++; 475 return e; 476} 477 478/// clear - Remove all entries from the ValueTable. 479void ValueTable::clear() { 480 valueNumbering.clear(); 481 expressionNumbering.clear(); 482 nextValueNumber = 1; 483} 484 485/// erase - Remove a value from the value numbering. 486void ValueTable::erase(Value *V) { 487 valueNumbering.erase(V); 488} 489 490/// verifyRemoved - Verify that the value is removed from all internal data 491/// structures. 492void ValueTable::verifyRemoved(const Value *V) const { 493 for (DenseMap<Value*, uint32_t>::const_iterator 494 I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) { 495 assert(I->first != V && "Inst still occurs in value numbering map!"); 496 } 497} 498 499//===----------------------------------------------------------------------===// 500// GVN Pass 501//===----------------------------------------------------------------------===// 502 503namespace { 504 class GVN; 505 struct AvailableValueInBlock { 506 /// BB - The basic block in question. 507 BasicBlock *BB; 508 enum ValType { 509 SimpleVal, // A simple offsetted value that is accessed. 510 LoadVal, // A value produced by a load. 511 MemIntrin, // A memory intrinsic which is loaded from. 512 UndefVal // A UndefValue representing a value from dead block (which 513 // is not yet physically removed from the CFG). 514 }; 515 516 /// V - The value that is live out of the block. 517 PointerIntPair<Value *, 2, ValType> Val; 518 519 /// Offset - The byte offset in Val that is interesting for the load query. 520 unsigned Offset; 521 522 static AvailableValueInBlock get(BasicBlock *BB, Value *V, 523 unsigned Offset = 0) { 524 AvailableValueInBlock Res; 525 Res.BB = BB; 526 Res.Val.setPointer(V); 527 Res.Val.setInt(SimpleVal); 528 Res.Offset = Offset; 529 return Res; 530 } 531 532 static AvailableValueInBlock getMI(BasicBlock *BB, MemIntrinsic *MI, 533 unsigned Offset = 0) { 534 AvailableValueInBlock Res; 535 Res.BB = BB; 536 Res.Val.setPointer(MI); 537 Res.Val.setInt(MemIntrin); 538 Res.Offset = Offset; 539 return Res; 540 } 541 542 static AvailableValueInBlock getLoad(BasicBlock *BB, LoadInst *LI, 543 unsigned Offset = 0) { 544 AvailableValueInBlock Res; 545 Res.BB = BB; 546 Res.Val.setPointer(LI); 547 Res.Val.setInt(LoadVal); 548 Res.Offset = Offset; 549 return Res; 550 } 551 552 static AvailableValueInBlock getUndef(BasicBlock *BB) { 553 AvailableValueInBlock Res; 554 Res.BB = BB; 555 Res.Val.setPointer(0); 556 Res.Val.setInt(UndefVal); 557 Res.Offset = 0; 558 return Res; 559 } 560 561 bool isSimpleValue() const { return Val.getInt() == SimpleVal; } 562 bool isCoercedLoadValue() const { return Val.getInt() == LoadVal; } 563 bool isMemIntrinValue() const { return Val.getInt() == MemIntrin; } 564 bool isUndefValue() const { return Val.getInt() == UndefVal; } 565 566 Value *getSimpleValue() const { 567 assert(isSimpleValue() && "Wrong accessor"); 568 return Val.getPointer(); 569 } 570 571 LoadInst *getCoercedLoadValue() const { 572 assert(isCoercedLoadValue() && "Wrong accessor"); 573 return cast<LoadInst>(Val.getPointer()); 574 } 575 576 MemIntrinsic *getMemIntrinValue() const { 577 assert(isMemIntrinValue() && "Wrong accessor"); 578 return cast<MemIntrinsic>(Val.getPointer()); 579 } 580 581 /// MaterializeAdjustedValue - Emit code into this block to adjust the value 582 /// defined here to the specified type. This handles various coercion cases. 583 Value *MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const; 584 }; 585 586 class GVN : public FunctionPass { 587 bool NoLoads; 588 MemoryDependenceAnalysis *MD; 589 DominatorTree *DT; 590 const DataLayout *TD; 591 const TargetLibraryInfo *TLI; 592 SetVector<BasicBlock *> DeadBlocks; 593 594 ValueTable VN; 595 596 /// LeaderTable - A mapping from value numbers to lists of Value*'s that 597 /// have that value number. Use findLeader to query it. 598 struct LeaderTableEntry { 599 Value *Val; 600 const BasicBlock *BB; 601 LeaderTableEntry *Next; 602 }; 603 DenseMap<uint32_t, LeaderTableEntry> LeaderTable; 604 BumpPtrAllocator TableAllocator; 605 606 SmallVector<Instruction*, 8> InstrsToErase; 607 608 typedef SmallVector<NonLocalDepResult, 64> LoadDepVect; 609 typedef SmallVector<AvailableValueInBlock, 64> AvailValInBlkVect; 610 typedef SmallVector<BasicBlock*, 64> UnavailBlkVect; 611 612 public: 613 static char ID; // Pass identification, replacement for typeid 614 explicit GVN(bool noloads = false) 615 : FunctionPass(ID), NoLoads(noloads), MD(0) { 616 initializeGVNPass(*PassRegistry::getPassRegistry()); 617 } 618 619 bool runOnFunction(Function &F); 620 621 /// markInstructionForDeletion - This removes the specified instruction from 622 /// our various maps and marks it for deletion. 623 void markInstructionForDeletion(Instruction *I) { 624 VN.erase(I); 625 InstrsToErase.push_back(I); 626 } 627 628 const DataLayout *getDataLayout() const { return TD; } 629 DominatorTree &getDominatorTree() const { return *DT; } 630 AliasAnalysis *getAliasAnalysis() const { return VN.getAliasAnalysis(); } 631 MemoryDependenceAnalysis &getMemDep() const { return *MD; } 632 private: 633 /// addToLeaderTable - Push a new Value to the LeaderTable onto the list for 634 /// its value number. 635 void addToLeaderTable(uint32_t N, Value *V, const BasicBlock *BB) { 636 LeaderTableEntry &Curr = LeaderTable[N]; 637 if (!Curr.Val) { 638 Curr.Val = V; 639 Curr.BB = BB; 640 return; 641 } 642 643 LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>(); 644 Node->Val = V; 645 Node->BB = BB; 646 Node->Next = Curr.Next; 647 Curr.Next = Node; 648 } 649 650 /// removeFromLeaderTable - Scan the list of values corresponding to a given 651 /// value number, and remove the given instruction if encountered. 652 void removeFromLeaderTable(uint32_t N, Instruction *I, BasicBlock *BB) { 653 LeaderTableEntry* Prev = 0; 654 LeaderTableEntry* Curr = &LeaderTable[N]; 655 656 while (Curr->Val != I || Curr->BB != BB) { 657 Prev = Curr; 658 Curr = Curr->Next; 659 } 660 661 if (Prev) { 662 Prev->Next = Curr->Next; 663 } else { 664 if (!Curr->Next) { 665 Curr->Val = 0; 666 Curr->BB = 0; 667 } else { 668 LeaderTableEntry* Next = Curr->Next; 669 Curr->Val = Next->Val; 670 Curr->BB = Next->BB; 671 Curr->Next = Next->Next; 672 } 673 } 674 } 675 676 // List of critical edges to be split between iterations. 677 SmallVector<std::pair<TerminatorInst*, unsigned>, 4> toSplit; 678 679 // This transformation requires dominator postdominator info 680 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 681 AU.addRequired<DominatorTree>(); 682 AU.addRequired<TargetLibraryInfo>(); 683 if (!NoLoads) 684 AU.addRequired<MemoryDependenceAnalysis>(); 685 AU.addRequired<AliasAnalysis>(); 686 687 AU.addPreserved<DominatorTree>(); 688 AU.addPreserved<AliasAnalysis>(); 689 } 690 691 692 // Helper fuctions of redundant load elimination 693 bool processLoad(LoadInst *L); 694 bool processNonLocalLoad(LoadInst *L); 695 void AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, 696 AvailValInBlkVect &ValuesPerBlock, 697 UnavailBlkVect &UnavailableBlocks); 698 bool PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock, 699 UnavailBlkVect &UnavailableBlocks); 700 701 // Other helper routines 702 bool processInstruction(Instruction *I); 703 bool processBlock(BasicBlock *BB); 704 void dump(DenseMap<uint32_t, Value*> &d); 705 bool iterateOnFunction(Function &F); 706 bool performPRE(Function &F); 707 Value *findLeader(const BasicBlock *BB, uint32_t num); 708 void cleanupGlobalSets(); 709 void verifyRemoved(const Instruction *I) const; 710 bool splitCriticalEdges(); 711 BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ); 712 unsigned replaceAllDominatedUsesWith(Value *From, Value *To, 713 const BasicBlockEdge &Root); 714 bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root); 715 bool processFoldableCondBr(BranchInst *BI); 716 void addDeadBlock(BasicBlock *BB); 717 void assignValNumForDeadCode(); 718 }; 719 720 char GVN::ID = 0; 721} 722 723// createGVNPass - The public interface to this file... 724FunctionPass *llvm::createGVNPass(bool NoLoads) { 725 return new GVN(NoLoads); 726} 727 728INITIALIZE_PASS_BEGIN(GVN, "gvn", "Global Value Numbering", false, false) 729INITIALIZE_PASS_DEPENDENCY(MemoryDependenceAnalysis) 730INITIALIZE_PASS_DEPENDENCY(DominatorTree) 731INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 732INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 733INITIALIZE_PASS_END(GVN, "gvn", "Global Value Numbering", false, false) 734 735#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 736void GVN::dump(DenseMap<uint32_t, Value*>& d) { 737 errs() << "{\n"; 738 for (DenseMap<uint32_t, Value*>::iterator I = d.begin(), 739 E = d.end(); I != E; ++I) { 740 errs() << I->first << "\n"; 741 I->second->dump(); 742 } 743 errs() << "}\n"; 744} 745#endif 746 747/// IsValueFullyAvailableInBlock - Return true if we can prove that the value 748/// we're analyzing is fully available in the specified block. As we go, keep 749/// track of which blocks we know are fully alive in FullyAvailableBlocks. This 750/// map is actually a tri-state map with the following values: 751/// 0) we know the block *is not* fully available. 752/// 1) we know the block *is* fully available. 753/// 2) we do not know whether the block is fully available or not, but we are 754/// currently speculating that it will be. 755/// 3) we are speculating for this block and have used that to speculate for 756/// other blocks. 757static bool IsValueFullyAvailableInBlock(BasicBlock *BB, 758 DenseMap<BasicBlock*, char> &FullyAvailableBlocks, 759 uint32_t RecurseDepth) { 760 if (RecurseDepth > MaxRecurseDepth) 761 return false; 762 763 // Optimistically assume that the block is fully available and check to see 764 // if we already know about this block in one lookup. 765 std::pair<DenseMap<BasicBlock*, char>::iterator, char> IV = 766 FullyAvailableBlocks.insert(std::make_pair(BB, 2)); 767 768 // If the entry already existed for this block, return the precomputed value. 769 if (!IV.second) { 770 // If this is a speculative "available" value, mark it as being used for 771 // speculation of other blocks. 772 if (IV.first->second == 2) 773 IV.first->second = 3; 774 return IV.first->second != 0; 775 } 776 777 // Otherwise, see if it is fully available in all predecessors. 778 pred_iterator PI = pred_begin(BB), PE = pred_end(BB); 779 780 // If this block has no predecessors, it isn't live-in here. 781 if (PI == PE) 782 goto SpeculationFailure; 783 784 for (; PI != PE; ++PI) 785 // If the value isn't fully available in one of our predecessors, then it 786 // isn't fully available in this block either. Undo our previous 787 // optimistic assumption and bail out. 788 if (!IsValueFullyAvailableInBlock(*PI, FullyAvailableBlocks,RecurseDepth+1)) 789 goto SpeculationFailure; 790 791 return true; 792 793// SpeculationFailure - If we get here, we found out that this is not, after 794// all, a fully-available block. We have a problem if we speculated on this and 795// used the speculation to mark other blocks as available. 796SpeculationFailure: 797 char &BBVal = FullyAvailableBlocks[BB]; 798 799 // If we didn't speculate on this, just return with it set to false. 800 if (BBVal == 2) { 801 BBVal = 0; 802 return false; 803 } 804 805 // If we did speculate on this value, we could have blocks set to 1 that are 806 // incorrect. Walk the (transitive) successors of this block and mark them as 807 // 0 if set to one. 808 SmallVector<BasicBlock*, 32> BBWorklist; 809 BBWorklist.push_back(BB); 810 811 do { 812 BasicBlock *Entry = BBWorklist.pop_back_val(); 813 // Note that this sets blocks to 0 (unavailable) if they happen to not 814 // already be in FullyAvailableBlocks. This is safe. 815 char &EntryVal = FullyAvailableBlocks[Entry]; 816 if (EntryVal == 0) continue; // Already unavailable. 817 818 // Mark as unavailable. 819 EntryVal = 0; 820 821 for (succ_iterator I = succ_begin(Entry), E = succ_end(Entry); I != E; ++I) 822 BBWorklist.push_back(*I); 823 } while (!BBWorklist.empty()); 824 825 return false; 826} 827 828 829/// CanCoerceMustAliasedValueToLoad - Return true if 830/// CoerceAvailableValueToLoadType will succeed. 831static bool CanCoerceMustAliasedValueToLoad(Value *StoredVal, 832 Type *LoadTy, 833 const DataLayout &TD) { 834 // If the loaded or stored value is an first class array or struct, don't try 835 // to transform them. We need to be able to bitcast to integer. 836 if (LoadTy->isStructTy() || LoadTy->isArrayTy() || 837 StoredVal->getType()->isStructTy() || 838 StoredVal->getType()->isArrayTy()) 839 return false; 840 841 // The store has to be at least as big as the load. 842 if (TD.getTypeSizeInBits(StoredVal->getType()) < 843 TD.getTypeSizeInBits(LoadTy)) 844 return false; 845 846 return true; 847} 848 849/// CoerceAvailableValueToLoadType - If we saw a store of a value to memory, and 850/// then a load from a must-aliased pointer of a different type, try to coerce 851/// the stored value. LoadedTy is the type of the load we want to replace and 852/// InsertPt is the place to insert new instructions. 853/// 854/// If we can't do it, return null. 855static Value *CoerceAvailableValueToLoadType(Value *StoredVal, 856 Type *LoadedTy, 857 Instruction *InsertPt, 858 const DataLayout &TD) { 859 if (!CanCoerceMustAliasedValueToLoad(StoredVal, LoadedTy, TD)) 860 return 0; 861 862 // If this is already the right type, just return it. 863 Type *StoredValTy = StoredVal->getType(); 864 865 uint64_t StoreSize = TD.getTypeSizeInBits(StoredValTy); 866 uint64_t LoadSize = TD.getTypeSizeInBits(LoadedTy); 867 868 // If the store and reload are the same size, we can always reuse it. 869 if (StoreSize == LoadSize) { 870 // Pointer to Pointer -> use bitcast. 871 if (StoredValTy->getScalarType()->isPointerTy() && 872 LoadedTy->getScalarType()->isPointerTy()) 873 return new BitCastInst(StoredVal, LoadedTy, "", InsertPt); 874 875 // Convert source pointers to integers, which can be bitcast. 876 if (StoredValTy->getScalarType()->isPointerTy()) { 877 StoredValTy = TD.getIntPtrType(StoredValTy); 878 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 879 } 880 881 Type *TypeToCastTo = LoadedTy; 882 if (TypeToCastTo->getScalarType()->isPointerTy()) 883 TypeToCastTo = TD.getIntPtrType(TypeToCastTo); 884 885 if (StoredValTy != TypeToCastTo) 886 StoredVal = new BitCastInst(StoredVal, TypeToCastTo, "", InsertPt); 887 888 // Cast to pointer if the load needs a pointer type. 889 if (LoadedTy->getScalarType()->isPointerTy()) 890 StoredVal = new IntToPtrInst(StoredVal, LoadedTy, "", InsertPt); 891 892 return StoredVal; 893 } 894 895 // If the loaded value is smaller than the available value, then we can 896 // extract out a piece from it. If the available value is too small, then we 897 // can't do anything. 898 assert(StoreSize >= LoadSize && "CanCoerceMustAliasedValueToLoad fail"); 899 900 // Convert source pointers to integers, which can be manipulated. 901 if (StoredValTy->getScalarType()->isPointerTy()) { 902 StoredValTy = TD.getIntPtrType(StoredValTy); 903 StoredVal = new PtrToIntInst(StoredVal, StoredValTy, "", InsertPt); 904 } 905 906 // Convert vectors and fp to integer, which can be manipulated. 907 if (!StoredValTy->isIntegerTy()) { 908 StoredValTy = IntegerType::get(StoredValTy->getContext(), StoreSize); 909 StoredVal = new BitCastInst(StoredVal, StoredValTy, "", InsertPt); 910 } 911 912 // If this is a big-endian system, we need to shift the value down to the low 913 // bits so that a truncate will work. 914 if (TD.isBigEndian()) { 915 Constant *Val = ConstantInt::get(StoredVal->getType(), StoreSize-LoadSize); 916 StoredVal = BinaryOperator::CreateLShr(StoredVal, Val, "tmp", InsertPt); 917 } 918 919 // Truncate the integer to the right size now. 920 Type *NewIntTy = IntegerType::get(StoredValTy->getContext(), LoadSize); 921 StoredVal = new TruncInst(StoredVal, NewIntTy, "trunc", InsertPt); 922 923 if (LoadedTy == NewIntTy) 924 return StoredVal; 925 926 // If the result is a pointer, inttoptr. 927 if (LoadedTy->getScalarType()->isPointerTy()) 928 return new IntToPtrInst(StoredVal, LoadedTy, "inttoptr", InsertPt); 929 930 // Otherwise, bitcast. 931 return new BitCastInst(StoredVal, LoadedTy, "bitcast", InsertPt); 932} 933 934/// AnalyzeLoadFromClobberingWrite - This function is called when we have a 935/// memdep query of a load that ends up being a clobbering memory write (store, 936/// memset, memcpy, memmove). This means that the write *may* provide bits used 937/// by the load but we can't be sure because the pointers don't mustalias. 938/// 939/// Check this case to see if there is anything more we can do before we give 940/// up. This returns -1 if we have to give up, or a byte number in the stored 941/// value of the piece that feeds the load. 942static int AnalyzeLoadFromClobberingWrite(Type *LoadTy, Value *LoadPtr, 943 Value *WritePtr, 944 uint64_t WriteSizeInBits, 945 const DataLayout &TD) { 946 // If the loaded or stored value is a first class array or struct, don't try 947 // to transform them. We need to be able to bitcast to integer. 948 if (LoadTy->isStructTy() || LoadTy->isArrayTy()) 949 return -1; 950 951 int64_t StoreOffset = 0, LoadOffset = 0; 952 Value *StoreBase = GetPointerBaseWithConstantOffset(WritePtr,StoreOffset,&TD); 953 Value *LoadBase = GetPointerBaseWithConstantOffset(LoadPtr, LoadOffset, &TD); 954 if (StoreBase != LoadBase) 955 return -1; 956 957 // If the load and store are to the exact same address, they should have been 958 // a must alias. AA must have gotten confused. 959 // FIXME: Study to see if/when this happens. One case is forwarding a memset 960 // to a load from the base of the memset. 961#if 0 962 if (LoadOffset == StoreOffset) { 963 dbgs() << "STORE/LOAD DEP WITH COMMON POINTER MISSED:\n" 964 << "Base = " << *StoreBase << "\n" 965 << "Store Ptr = " << *WritePtr << "\n" 966 << "Store Offs = " << StoreOffset << "\n" 967 << "Load Ptr = " << *LoadPtr << "\n"; 968 abort(); 969 } 970#endif 971 972 // If the load and store don't overlap at all, the store doesn't provide 973 // anything to the load. In this case, they really don't alias at all, AA 974 // must have gotten confused. 975 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy); 976 977 if ((WriteSizeInBits & 7) | (LoadSize & 7)) 978 return -1; 979 uint64_t StoreSize = WriteSizeInBits >> 3; // Convert to bytes. 980 LoadSize >>= 3; 981 982 983 bool isAAFailure = false; 984 if (StoreOffset < LoadOffset) 985 isAAFailure = StoreOffset+int64_t(StoreSize) <= LoadOffset; 986 else 987 isAAFailure = LoadOffset+int64_t(LoadSize) <= StoreOffset; 988 989 if (isAAFailure) { 990#if 0 991 dbgs() << "STORE LOAD DEP WITH COMMON BASE:\n" 992 << "Base = " << *StoreBase << "\n" 993 << "Store Ptr = " << *WritePtr << "\n" 994 << "Store Offs = " << StoreOffset << "\n" 995 << "Load Ptr = " << *LoadPtr << "\n"; 996 abort(); 997#endif 998 return -1; 999 } 1000 1001 // If the Load isn't completely contained within the stored bits, we don't 1002 // have all the bits to feed it. We could do something crazy in the future 1003 // (issue a smaller load then merge the bits in) but this seems unlikely to be 1004 // valuable. 1005 if (StoreOffset > LoadOffset || 1006 StoreOffset+StoreSize < LoadOffset+LoadSize) 1007 return -1; 1008 1009 // Okay, we can do this transformation. Return the number of bytes into the 1010 // store that the load is. 1011 return LoadOffset-StoreOffset; 1012} 1013 1014/// AnalyzeLoadFromClobberingStore - This function is called when we have a 1015/// memdep query of a load that ends up being a clobbering store. 1016static int AnalyzeLoadFromClobberingStore(Type *LoadTy, Value *LoadPtr, 1017 StoreInst *DepSI, 1018 const DataLayout &TD) { 1019 // Cannot handle reading from store of first-class aggregate yet. 1020 if (DepSI->getValueOperand()->getType()->isStructTy() || 1021 DepSI->getValueOperand()->getType()->isArrayTy()) 1022 return -1; 1023 1024 Value *StorePtr = DepSI->getPointerOperand(); 1025 uint64_t StoreSize =TD.getTypeSizeInBits(DepSI->getValueOperand()->getType()); 1026 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1027 StorePtr, StoreSize, TD); 1028} 1029 1030/// AnalyzeLoadFromClobberingLoad - This function is called when we have a 1031/// memdep query of a load that ends up being clobbered by another load. See if 1032/// the other load can feed into the second load. 1033static int AnalyzeLoadFromClobberingLoad(Type *LoadTy, Value *LoadPtr, 1034 LoadInst *DepLI, const DataLayout &TD){ 1035 // Cannot handle reading from store of first-class aggregate yet. 1036 if (DepLI->getType()->isStructTy() || DepLI->getType()->isArrayTy()) 1037 return -1; 1038 1039 Value *DepPtr = DepLI->getPointerOperand(); 1040 uint64_t DepSize = TD.getTypeSizeInBits(DepLI->getType()); 1041 int R = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, DepSize, TD); 1042 if (R != -1) return R; 1043 1044 // If we have a load/load clobber an DepLI can be widened to cover this load, 1045 // then we should widen it! 1046 int64_t LoadOffs = 0; 1047 const Value *LoadBase = 1048 GetPointerBaseWithConstantOffset(LoadPtr, LoadOffs, &TD); 1049 unsigned LoadSize = TD.getTypeStoreSize(LoadTy); 1050 1051 unsigned Size = MemoryDependenceAnalysis:: 1052 getLoadLoadClobberFullWidthSize(LoadBase, LoadOffs, LoadSize, DepLI, TD); 1053 if (Size == 0) return -1; 1054 1055 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, DepPtr, Size*8, TD); 1056} 1057 1058 1059 1060static int AnalyzeLoadFromClobberingMemInst(Type *LoadTy, Value *LoadPtr, 1061 MemIntrinsic *MI, 1062 const DataLayout &TD) { 1063 // If the mem operation is a non-constant size, we can't handle it. 1064 ConstantInt *SizeCst = dyn_cast<ConstantInt>(MI->getLength()); 1065 if (SizeCst == 0) return -1; 1066 uint64_t MemSizeInBits = SizeCst->getZExtValue()*8; 1067 1068 // If this is memset, we just need to see if the offset is valid in the size 1069 // of the memset.. 1070 if (MI->getIntrinsicID() == Intrinsic::memset) 1071 return AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, MI->getDest(), 1072 MemSizeInBits, TD); 1073 1074 // If we have a memcpy/memmove, the only case we can handle is if this is a 1075 // copy from constant memory. In that case, we can read directly from the 1076 // constant memory. 1077 MemTransferInst *MTI = cast<MemTransferInst>(MI); 1078 1079 Constant *Src = dyn_cast<Constant>(MTI->getSource()); 1080 if (Src == 0) return -1; 1081 1082 GlobalVariable *GV = dyn_cast<GlobalVariable>(GetUnderlyingObject(Src, &TD)); 1083 if (GV == 0 || !GV->isConstant()) return -1; 1084 1085 // See if the access is within the bounds of the transfer. 1086 int Offset = AnalyzeLoadFromClobberingWrite(LoadTy, LoadPtr, 1087 MI->getDest(), MemSizeInBits, TD); 1088 if (Offset == -1) 1089 return Offset; 1090 1091 // Otherwise, see if we can constant fold a load from the constant with the 1092 // offset applied as appropriate. 1093 Src = ConstantExpr::getBitCast(Src, 1094 llvm::Type::getInt8PtrTy(Src->getContext())); 1095 Constant *OffsetCst = 1096 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1097 Src = ConstantExpr::getGetElementPtr(Src, OffsetCst); 1098 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1099 if (ConstantFoldLoadFromConstPtr(Src, &TD)) 1100 return Offset; 1101 return -1; 1102} 1103 1104 1105/// GetStoreValueForLoad - This function is called when we have a 1106/// memdep query of a load that ends up being a clobbering store. This means 1107/// that the store provides bits used by the load but we the pointers don't 1108/// mustalias. Check this case to see if there is anything more we can do 1109/// before we give up. 1110static Value *GetStoreValueForLoad(Value *SrcVal, unsigned Offset, 1111 Type *LoadTy, 1112 Instruction *InsertPt, const DataLayout &TD){ 1113 LLVMContext &Ctx = SrcVal->getType()->getContext(); 1114 1115 uint64_t StoreSize = (TD.getTypeSizeInBits(SrcVal->getType()) + 7) / 8; 1116 uint64_t LoadSize = (TD.getTypeSizeInBits(LoadTy) + 7) / 8; 1117 1118 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1119 1120 // Compute which bits of the stored value are being used by the load. Convert 1121 // to an integer type to start with. 1122 if (SrcVal->getType()->getScalarType()->isPointerTy()) 1123 SrcVal = Builder.CreatePtrToInt(SrcVal, 1124 TD.getIntPtrType(SrcVal->getType())); 1125 if (!SrcVal->getType()->isIntegerTy()) 1126 SrcVal = Builder.CreateBitCast(SrcVal, IntegerType::get(Ctx, StoreSize*8)); 1127 1128 // Shift the bits to the least significant depending on endianness. 1129 unsigned ShiftAmt; 1130 if (TD.isLittleEndian()) 1131 ShiftAmt = Offset*8; 1132 else 1133 ShiftAmt = (StoreSize-LoadSize-Offset)*8; 1134 1135 if (ShiftAmt) 1136 SrcVal = Builder.CreateLShr(SrcVal, ShiftAmt); 1137 1138 if (LoadSize != StoreSize) 1139 SrcVal = Builder.CreateTrunc(SrcVal, IntegerType::get(Ctx, LoadSize*8)); 1140 1141 return CoerceAvailableValueToLoadType(SrcVal, LoadTy, InsertPt, TD); 1142} 1143 1144/// GetLoadValueForLoad - This function is called when we have a 1145/// memdep query of a load that ends up being a clobbering load. This means 1146/// that the load *may* provide bits used by the load but we can't be sure 1147/// because the pointers don't mustalias. Check this case to see if there is 1148/// anything more we can do before we give up. 1149static Value *GetLoadValueForLoad(LoadInst *SrcVal, unsigned Offset, 1150 Type *LoadTy, Instruction *InsertPt, 1151 GVN &gvn) { 1152 const DataLayout &TD = *gvn.getDataLayout(); 1153 // If Offset+LoadTy exceeds the size of SrcVal, then we must be wanting to 1154 // widen SrcVal out to a larger load. 1155 unsigned SrcValSize = TD.getTypeStoreSize(SrcVal->getType()); 1156 unsigned LoadSize = TD.getTypeStoreSize(LoadTy); 1157 if (Offset+LoadSize > SrcValSize) { 1158 assert(SrcVal->isSimple() && "Cannot widen volatile/atomic load!"); 1159 assert(SrcVal->getType()->isIntegerTy() && "Can't widen non-integer load"); 1160 // If we have a load/load clobber an DepLI can be widened to cover this 1161 // load, then we should widen it to the next power of 2 size big enough! 1162 unsigned NewLoadSize = Offset+LoadSize; 1163 if (!isPowerOf2_32(NewLoadSize)) 1164 NewLoadSize = NextPowerOf2(NewLoadSize); 1165 1166 Value *PtrVal = SrcVal->getPointerOperand(); 1167 1168 // Insert the new load after the old load. This ensures that subsequent 1169 // memdep queries will find the new load. We can't easily remove the old 1170 // load completely because it is already in the value numbering table. 1171 IRBuilder<> Builder(SrcVal->getParent(), ++BasicBlock::iterator(SrcVal)); 1172 Type *DestPTy = 1173 IntegerType::get(LoadTy->getContext(), NewLoadSize*8); 1174 DestPTy = PointerType::get(DestPTy, 1175 PtrVal->getType()->getPointerAddressSpace()); 1176 Builder.SetCurrentDebugLocation(SrcVal->getDebugLoc()); 1177 PtrVal = Builder.CreateBitCast(PtrVal, DestPTy); 1178 LoadInst *NewLoad = Builder.CreateLoad(PtrVal); 1179 NewLoad->takeName(SrcVal); 1180 NewLoad->setAlignment(SrcVal->getAlignment()); 1181 1182 DEBUG(dbgs() << "GVN WIDENED LOAD: " << *SrcVal << "\n"); 1183 DEBUG(dbgs() << "TO: " << *NewLoad << "\n"); 1184 1185 // Replace uses of the original load with the wider load. On a big endian 1186 // system, we need to shift down to get the relevant bits. 1187 Value *RV = NewLoad; 1188 if (TD.isBigEndian()) 1189 RV = Builder.CreateLShr(RV, 1190 NewLoadSize*8-SrcVal->getType()->getPrimitiveSizeInBits()); 1191 RV = Builder.CreateTrunc(RV, SrcVal->getType()); 1192 SrcVal->replaceAllUsesWith(RV); 1193 1194 // We would like to use gvn.markInstructionForDeletion here, but we can't 1195 // because the load is already memoized into the leader map table that GVN 1196 // tracks. It is potentially possible to remove the load from the table, 1197 // but then there all of the operations based on it would need to be 1198 // rehashed. Just leave the dead load around. 1199 gvn.getMemDep().removeInstruction(SrcVal); 1200 SrcVal = NewLoad; 1201 } 1202 1203 return GetStoreValueForLoad(SrcVal, Offset, LoadTy, InsertPt, TD); 1204} 1205 1206 1207/// GetMemInstValueForLoad - This function is called when we have a 1208/// memdep query of a load that ends up being a clobbering mem intrinsic. 1209static Value *GetMemInstValueForLoad(MemIntrinsic *SrcInst, unsigned Offset, 1210 Type *LoadTy, Instruction *InsertPt, 1211 const DataLayout &TD){ 1212 LLVMContext &Ctx = LoadTy->getContext(); 1213 uint64_t LoadSize = TD.getTypeSizeInBits(LoadTy)/8; 1214 1215 IRBuilder<> Builder(InsertPt->getParent(), InsertPt); 1216 1217 // We know that this method is only called when the mem transfer fully 1218 // provides the bits for the load. 1219 if (MemSetInst *MSI = dyn_cast<MemSetInst>(SrcInst)) { 1220 // memset(P, 'x', 1234) -> splat('x'), even if x is a variable, and 1221 // independently of what the offset is. 1222 Value *Val = MSI->getValue(); 1223 if (LoadSize != 1) 1224 Val = Builder.CreateZExt(Val, IntegerType::get(Ctx, LoadSize*8)); 1225 1226 Value *OneElt = Val; 1227 1228 // Splat the value out to the right number of bits. 1229 for (unsigned NumBytesSet = 1; NumBytesSet != LoadSize; ) { 1230 // If we can double the number of bytes set, do it. 1231 if (NumBytesSet*2 <= LoadSize) { 1232 Value *ShVal = Builder.CreateShl(Val, NumBytesSet*8); 1233 Val = Builder.CreateOr(Val, ShVal); 1234 NumBytesSet <<= 1; 1235 continue; 1236 } 1237 1238 // Otherwise insert one byte at a time. 1239 Value *ShVal = Builder.CreateShl(Val, 1*8); 1240 Val = Builder.CreateOr(OneElt, ShVal); 1241 ++NumBytesSet; 1242 } 1243 1244 return CoerceAvailableValueToLoadType(Val, LoadTy, InsertPt, TD); 1245 } 1246 1247 // Otherwise, this is a memcpy/memmove from a constant global. 1248 MemTransferInst *MTI = cast<MemTransferInst>(SrcInst); 1249 Constant *Src = cast<Constant>(MTI->getSource()); 1250 1251 // Otherwise, see if we can constant fold a load from the constant with the 1252 // offset applied as appropriate. 1253 Src = ConstantExpr::getBitCast(Src, 1254 llvm::Type::getInt8PtrTy(Src->getContext())); 1255 Constant *OffsetCst = 1256 ConstantInt::get(Type::getInt64Ty(Src->getContext()), (unsigned)Offset); 1257 Src = ConstantExpr::getGetElementPtr(Src, OffsetCst); 1258 Src = ConstantExpr::getBitCast(Src, PointerType::getUnqual(LoadTy)); 1259 return ConstantFoldLoadFromConstPtr(Src, &TD); 1260} 1261 1262 1263/// ConstructSSAForLoadSet - Given a set of loads specified by ValuesPerBlock, 1264/// construct SSA form, allowing us to eliminate LI. This returns the value 1265/// that should be used at LI's definition site. 1266static Value *ConstructSSAForLoadSet(LoadInst *LI, 1267 SmallVectorImpl<AvailableValueInBlock> &ValuesPerBlock, 1268 GVN &gvn) { 1269 // Check for the fully redundant, dominating load case. In this case, we can 1270 // just use the dominating value directly. 1271 if (ValuesPerBlock.size() == 1 && 1272 gvn.getDominatorTree().properlyDominates(ValuesPerBlock[0].BB, 1273 LI->getParent())) { 1274 assert(!ValuesPerBlock[0].isUndefValue() && "Dead BB dominate this block"); 1275 return ValuesPerBlock[0].MaterializeAdjustedValue(LI->getType(), gvn); 1276 } 1277 1278 // Otherwise, we have to construct SSA form. 1279 SmallVector<PHINode*, 8> NewPHIs; 1280 SSAUpdater SSAUpdate(&NewPHIs); 1281 SSAUpdate.Initialize(LI->getType(), LI->getName()); 1282 1283 Type *LoadTy = LI->getType(); 1284 1285 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) { 1286 const AvailableValueInBlock &AV = ValuesPerBlock[i]; 1287 BasicBlock *BB = AV.BB; 1288 1289 if (SSAUpdate.HasValueForBlock(BB)) 1290 continue; 1291 1292 SSAUpdate.AddAvailableValue(BB, AV.MaterializeAdjustedValue(LoadTy, gvn)); 1293 } 1294 1295 // Perform PHI construction. 1296 Value *V = SSAUpdate.GetValueInMiddleOfBlock(LI->getParent()); 1297 1298 // If new PHI nodes were created, notify alias analysis. 1299 if (V->getType()->getScalarType()->isPointerTy()) { 1300 AliasAnalysis *AA = gvn.getAliasAnalysis(); 1301 1302 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) 1303 AA->copyValue(LI, NewPHIs[i]); 1304 1305 // Now that we've copied information to the new PHIs, scan through 1306 // them again and inform alias analysis that we've added potentially 1307 // escaping uses to any values that are operands to these PHIs. 1308 for (unsigned i = 0, e = NewPHIs.size(); i != e; ++i) { 1309 PHINode *P = NewPHIs[i]; 1310 for (unsigned ii = 0, ee = P->getNumIncomingValues(); ii != ee; ++ii) { 1311 unsigned jj = PHINode::getOperandNumForIncomingValue(ii); 1312 AA->addEscapingUse(P->getOperandUse(jj)); 1313 } 1314 } 1315 } 1316 1317 return V; 1318} 1319 1320Value *AvailableValueInBlock::MaterializeAdjustedValue(Type *LoadTy, GVN &gvn) const { 1321 Value *Res; 1322 if (isSimpleValue()) { 1323 Res = getSimpleValue(); 1324 if (Res->getType() != LoadTy) { 1325 const DataLayout *TD = gvn.getDataLayout(); 1326 assert(TD && "Need target data to handle type mismatch case"); 1327 Res = GetStoreValueForLoad(Res, Offset, LoadTy, BB->getTerminator(), 1328 *TD); 1329 1330 DEBUG(dbgs() << "GVN COERCED NONLOCAL VAL:\nOffset: " << Offset << " " 1331 << *getSimpleValue() << '\n' 1332 << *Res << '\n' << "\n\n\n"); 1333 } 1334 } else if (isCoercedLoadValue()) { 1335 LoadInst *Load = getCoercedLoadValue(); 1336 if (Load->getType() == LoadTy && Offset == 0) { 1337 Res = Load; 1338 } else { 1339 Res = GetLoadValueForLoad(Load, Offset, LoadTy, BB->getTerminator(), 1340 gvn); 1341 1342 DEBUG(dbgs() << "GVN COERCED NONLOCAL LOAD:\nOffset: " << Offset << " " 1343 << *getCoercedLoadValue() << '\n' 1344 << *Res << '\n' << "\n\n\n"); 1345 } 1346 } else if (isMemIntrinValue()) { 1347 const DataLayout *TD = gvn.getDataLayout(); 1348 assert(TD && "Need target data to handle type mismatch case"); 1349 Res = GetMemInstValueForLoad(getMemIntrinValue(), Offset, 1350 LoadTy, BB->getTerminator(), *TD); 1351 DEBUG(dbgs() << "GVN COERCED NONLOCAL MEM INTRIN:\nOffset: " << Offset 1352 << " " << *getMemIntrinValue() << '\n' 1353 << *Res << '\n' << "\n\n\n"); 1354 } else { 1355 assert(isUndefValue() && "Should be UndefVal"); 1356 DEBUG(dbgs() << "GVN COERCED NONLOCAL Undef:\n";); 1357 return UndefValue::get(LoadTy); 1358 } 1359 return Res; 1360} 1361 1362static bool isLifetimeStart(const Instruction *Inst) { 1363 if (const IntrinsicInst* II = dyn_cast<IntrinsicInst>(Inst)) 1364 return II->getIntrinsicID() == Intrinsic::lifetime_start; 1365 return false; 1366} 1367 1368void GVN::AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps, 1369 AvailValInBlkVect &ValuesPerBlock, 1370 UnavailBlkVect &UnavailableBlocks) { 1371 1372 // Filter out useless results (non-locals, etc). Keep track of the blocks 1373 // where we have a value available in repl, also keep track of whether we see 1374 // dependencies that produce an unknown value for the load (such as a call 1375 // that could potentially clobber the load). 1376 unsigned NumDeps = Deps.size(); 1377 for (unsigned i = 0, e = NumDeps; i != e; ++i) { 1378 BasicBlock *DepBB = Deps[i].getBB(); 1379 MemDepResult DepInfo = Deps[i].getResult(); 1380 1381 if (DeadBlocks.count(DepBB)) { 1382 // Dead dependent mem-op disguise as a load evaluating the same value 1383 // as the load in question. 1384 ValuesPerBlock.push_back(AvailableValueInBlock::getUndef(DepBB)); 1385 continue; 1386 } 1387 1388 if (!DepInfo.isDef() && !DepInfo.isClobber()) { 1389 UnavailableBlocks.push_back(DepBB); 1390 continue; 1391 } 1392 1393 if (DepInfo.isClobber()) { 1394 // The address being loaded in this non-local block may not be the same as 1395 // the pointer operand of the load if PHI translation occurs. Make sure 1396 // to consider the right address. 1397 Value *Address = Deps[i].getAddress(); 1398 1399 // If the dependence is to a store that writes to a superset of the bits 1400 // read by the load, we can extract the bits we need for the load from the 1401 // stored value. 1402 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInfo.getInst())) { 1403 if (TD && Address) { 1404 int Offset = AnalyzeLoadFromClobberingStore(LI->getType(), Address, 1405 DepSI, *TD); 1406 if (Offset != -1) { 1407 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1408 DepSI->getValueOperand(), 1409 Offset)); 1410 continue; 1411 } 1412 } 1413 } 1414 1415 // Check to see if we have something like this: 1416 // load i32* P 1417 // load i8* (P+1) 1418 // if we have this, replace the later with an extraction from the former. 1419 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInfo.getInst())) { 1420 // If this is a clobber and L is the first instruction in its block, then 1421 // we have the first instruction in the entry block. 1422 if (DepLI != LI && Address && TD) { 1423 int Offset = AnalyzeLoadFromClobberingLoad(LI->getType(), 1424 LI->getPointerOperand(), 1425 DepLI, *TD); 1426 1427 if (Offset != -1) { 1428 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB,DepLI, 1429 Offset)); 1430 continue; 1431 } 1432 } 1433 } 1434 1435 // If the clobbering value is a memset/memcpy/memmove, see if we can 1436 // forward a value on from it. 1437 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(DepInfo.getInst())) { 1438 if (TD && Address) { 1439 int Offset = AnalyzeLoadFromClobberingMemInst(LI->getType(), Address, 1440 DepMI, *TD); 1441 if (Offset != -1) { 1442 ValuesPerBlock.push_back(AvailableValueInBlock::getMI(DepBB, DepMI, 1443 Offset)); 1444 continue; 1445 } 1446 } 1447 } 1448 1449 UnavailableBlocks.push_back(DepBB); 1450 continue; 1451 } 1452 1453 // DepInfo.isDef() here 1454 1455 Instruction *DepInst = DepInfo.getInst(); 1456 1457 // Loading the allocation -> undef. 1458 if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI) || 1459 // Loading immediately after lifetime begin -> undef. 1460 isLifetimeStart(DepInst)) { 1461 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1462 UndefValue::get(LI->getType()))); 1463 continue; 1464 } 1465 1466 if (StoreInst *S = dyn_cast<StoreInst>(DepInst)) { 1467 // Reject loads and stores that are to the same address but are of 1468 // different types if we have to. 1469 if (S->getValueOperand()->getType() != LI->getType()) { 1470 // If the stored value is larger or equal to the loaded value, we can 1471 // reuse it. 1472 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(S->getValueOperand(), 1473 LI->getType(), *TD)) { 1474 UnavailableBlocks.push_back(DepBB); 1475 continue; 1476 } 1477 } 1478 1479 ValuesPerBlock.push_back(AvailableValueInBlock::get(DepBB, 1480 S->getValueOperand())); 1481 continue; 1482 } 1483 1484 if (LoadInst *LD = dyn_cast<LoadInst>(DepInst)) { 1485 // If the types mismatch and we can't handle it, reject reuse of the load. 1486 if (LD->getType() != LI->getType()) { 1487 // If the stored value is larger or equal to the loaded value, we can 1488 // reuse it. 1489 if (TD == 0 || !CanCoerceMustAliasedValueToLoad(LD, LI->getType(),*TD)){ 1490 UnavailableBlocks.push_back(DepBB); 1491 continue; 1492 } 1493 } 1494 ValuesPerBlock.push_back(AvailableValueInBlock::getLoad(DepBB, LD)); 1495 continue; 1496 } 1497 1498 UnavailableBlocks.push_back(DepBB); 1499 } 1500} 1501 1502bool GVN::PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock, 1503 UnavailBlkVect &UnavailableBlocks) { 1504 // Okay, we have *some* definitions of the value. This means that the value 1505 // is available in some of our (transitive) predecessors. Lets think about 1506 // doing PRE of this load. This will involve inserting a new load into the 1507 // predecessor when it's not available. We could do this in general, but 1508 // prefer to not increase code size. As such, we only do this when we know 1509 // that we only have to insert *one* load (which means we're basically moving 1510 // the load, not inserting a new one). 1511 1512 SmallPtrSet<BasicBlock *, 4> Blockers; 1513 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1514 Blockers.insert(UnavailableBlocks[i]); 1515 1516 // Let's find the first basic block with more than one predecessor. Walk 1517 // backwards through predecessors if needed. 1518 BasicBlock *LoadBB = LI->getParent(); 1519 BasicBlock *TmpBB = LoadBB; 1520 1521 while (TmpBB->getSinglePredecessor()) { 1522 TmpBB = TmpBB->getSinglePredecessor(); 1523 if (TmpBB == LoadBB) // Infinite (unreachable) loop. 1524 return false; 1525 if (Blockers.count(TmpBB)) 1526 return false; 1527 1528 // If any of these blocks has more than one successor (i.e. if the edge we 1529 // just traversed was critical), then there are other paths through this 1530 // block along which the load may not be anticipated. Hoisting the load 1531 // above this block would be adding the load to execution paths along 1532 // which it was not previously executed. 1533 if (TmpBB->getTerminator()->getNumSuccessors() != 1) 1534 return false; 1535 } 1536 1537 assert(TmpBB); 1538 LoadBB = TmpBB; 1539 1540 // Check to see how many predecessors have the loaded value fully 1541 // available. 1542 DenseMap<BasicBlock*, Value*> PredLoads; 1543 DenseMap<BasicBlock*, char> FullyAvailableBlocks; 1544 for (unsigned i = 0, e = ValuesPerBlock.size(); i != e; ++i) 1545 FullyAvailableBlocks[ValuesPerBlock[i].BB] = true; 1546 for (unsigned i = 0, e = UnavailableBlocks.size(); i != e; ++i) 1547 FullyAvailableBlocks[UnavailableBlocks[i]] = false; 1548 1549 SmallVector<BasicBlock *, 4> CriticalEdgePred; 1550 for (pred_iterator PI = pred_begin(LoadBB), E = pred_end(LoadBB); 1551 PI != E; ++PI) { 1552 BasicBlock *Pred = *PI; 1553 if (IsValueFullyAvailableInBlock(Pred, FullyAvailableBlocks, 0)) { 1554 continue; 1555 } 1556 PredLoads[Pred] = 0; 1557 1558 if (Pred->getTerminator()->getNumSuccessors() != 1) { 1559 if (isa<IndirectBrInst>(Pred->getTerminator())) { 1560 DEBUG(dbgs() << "COULD NOT PRE LOAD BECAUSE OF INDBR CRITICAL EDGE '" 1561 << Pred->getName() << "': " << *LI << '\n'); 1562 return false; 1563 } 1564 1565 if (LoadBB->isLandingPad()) { 1566 DEBUG(dbgs() 1567 << "COULD NOT PRE LOAD BECAUSE OF LANDING PAD CRITICAL EDGE '" 1568 << Pred->getName() << "': " << *LI << '\n'); 1569 return false; 1570 } 1571 1572 CriticalEdgePred.push_back(Pred); 1573 } 1574 } 1575 1576 // Decide whether PRE is profitable for this load. 1577 unsigned NumUnavailablePreds = PredLoads.size(); 1578 assert(NumUnavailablePreds != 0 && 1579 "Fully available value should already be eliminated!"); 1580 1581 // If this load is unavailable in multiple predecessors, reject it. 1582 // FIXME: If we could restructure the CFG, we could make a common pred with 1583 // all the preds that don't have an available LI and insert a new load into 1584 // that one block. 1585 if (NumUnavailablePreds != 1) 1586 return false; 1587 1588 // Split critical edges, and update the unavailable predecessors accordingly. 1589 for (SmallVectorImpl<BasicBlock *>::iterator I = CriticalEdgePred.begin(), 1590 E = CriticalEdgePred.end(); I != E; I++) { 1591 BasicBlock *OrigPred = *I; 1592 BasicBlock *NewPred = splitCriticalEdges(OrigPred, LoadBB); 1593 PredLoads.erase(OrigPred); 1594 PredLoads[NewPred] = 0; 1595 DEBUG(dbgs() << "Split critical edge " << OrigPred->getName() << "->" 1596 << LoadBB->getName() << '\n'); 1597 } 1598 1599 // Check if the load can safely be moved to all the unavailable predecessors. 1600 bool CanDoPRE = true; 1601 SmallVector<Instruction*, 8> NewInsts; 1602 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1603 E = PredLoads.end(); I != E; ++I) { 1604 BasicBlock *UnavailablePred = I->first; 1605 1606 // Do PHI translation to get its value in the predecessor if necessary. The 1607 // returned pointer (if non-null) is guaranteed to dominate UnavailablePred. 1608 1609 // If all preds have a single successor, then we know it is safe to insert 1610 // the load on the pred (?!?), so we can insert code to materialize the 1611 // pointer if it is not available. 1612 PHITransAddr Address(LI->getPointerOperand(), TD); 1613 Value *LoadPtr = 0; 1614 LoadPtr = Address.PHITranslateWithInsertion(LoadBB, UnavailablePred, 1615 *DT, NewInsts); 1616 1617 // If we couldn't find or insert a computation of this phi translated value, 1618 // we fail PRE. 1619 if (LoadPtr == 0) { 1620 DEBUG(dbgs() << "COULDN'T INSERT PHI TRANSLATED VALUE OF: " 1621 << *LI->getPointerOperand() << "\n"); 1622 CanDoPRE = false; 1623 break; 1624 } 1625 1626 I->second = LoadPtr; 1627 } 1628 1629 if (!CanDoPRE) { 1630 while (!NewInsts.empty()) { 1631 Instruction *I = NewInsts.pop_back_val(); 1632 if (MD) MD->removeInstruction(I); 1633 I->eraseFromParent(); 1634 } 1635 // HINT:Don't revert the edge-splitting as following transformation may 1636 // also need to split these critial edges. 1637 return !CriticalEdgePred.empty(); 1638 } 1639 1640 // Okay, we can eliminate this load by inserting a reload in the predecessor 1641 // and using PHI construction to get the value in the other predecessors, do 1642 // it. 1643 DEBUG(dbgs() << "GVN REMOVING PRE LOAD: " << *LI << '\n'); 1644 DEBUG(if (!NewInsts.empty()) 1645 dbgs() << "INSERTED " << NewInsts.size() << " INSTS: " 1646 << *NewInsts.back() << '\n'); 1647 1648 // Assign value numbers to the new instructions. 1649 for (unsigned i = 0, e = NewInsts.size(); i != e; ++i) { 1650 // FIXME: We really _ought_ to insert these value numbers into their 1651 // parent's availability map. However, in doing so, we risk getting into 1652 // ordering issues. If a block hasn't been processed yet, we would be 1653 // marking a value as AVAIL-IN, which isn't what we intend. 1654 VN.lookup_or_add(NewInsts[i]); 1655 } 1656 1657 for (DenseMap<BasicBlock*, Value*>::iterator I = PredLoads.begin(), 1658 E = PredLoads.end(); I != E; ++I) { 1659 BasicBlock *UnavailablePred = I->first; 1660 Value *LoadPtr = I->second; 1661 1662 Instruction *NewLoad = new LoadInst(LoadPtr, LI->getName()+".pre", false, 1663 LI->getAlignment(), 1664 UnavailablePred->getTerminator()); 1665 1666 // Transfer the old load's TBAA tag to the new load. 1667 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) 1668 NewLoad->setMetadata(LLVMContext::MD_tbaa, Tag); 1669 1670 // Transfer DebugLoc. 1671 NewLoad->setDebugLoc(LI->getDebugLoc()); 1672 1673 // Add the newly created load. 1674 ValuesPerBlock.push_back(AvailableValueInBlock::get(UnavailablePred, 1675 NewLoad)); 1676 MD->invalidateCachedPointerInfo(LoadPtr); 1677 DEBUG(dbgs() << "GVN INSERTED " << *NewLoad << '\n'); 1678 } 1679 1680 // Perform PHI construction. 1681 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); 1682 LI->replaceAllUsesWith(V); 1683 if (isa<PHINode>(V)) 1684 V->takeName(LI); 1685 if (V->getType()->getScalarType()->isPointerTy()) 1686 MD->invalidateCachedPointerInfo(V); 1687 markInstructionForDeletion(LI); 1688 ++NumPRELoad; 1689 return true; 1690} 1691 1692/// processNonLocalLoad - Attempt to eliminate a load whose dependencies are 1693/// non-local by performing PHI construction. 1694bool GVN::processNonLocalLoad(LoadInst *LI) { 1695 // Step 1: Find the non-local dependencies of the load. 1696 LoadDepVect Deps; 1697 AliasAnalysis::Location Loc = VN.getAliasAnalysis()->getLocation(LI); 1698 MD->getNonLocalPointerDependency(Loc, true, LI->getParent(), Deps); 1699 1700 // If we had to process more than one hundred blocks to find the 1701 // dependencies, this load isn't worth worrying about. Optimizing 1702 // it will be too expensive. 1703 unsigned NumDeps = Deps.size(); 1704 if (NumDeps > 100) 1705 return false; 1706 1707 // If we had a phi translation failure, we'll have a single entry which is a 1708 // clobber in the current block. Reject this early. 1709 if (NumDeps == 1 && 1710 !Deps[0].getResult().isDef() && !Deps[0].getResult().isClobber()) { 1711 DEBUG( 1712 dbgs() << "GVN: non-local load "; 1713 WriteAsOperand(dbgs(), LI); 1714 dbgs() << " has unknown dependencies\n"; 1715 ); 1716 return false; 1717 } 1718 1719 // Step 2: Analyze the availability of the load 1720 AvailValInBlkVect ValuesPerBlock; 1721 UnavailBlkVect UnavailableBlocks; 1722 AnalyzeLoadAvailability(LI, Deps, ValuesPerBlock, UnavailableBlocks); 1723 1724 // If we have no predecessors that produce a known value for this load, exit 1725 // early. 1726 if (ValuesPerBlock.empty()) 1727 return false; 1728 1729 // Step 3: Eliminate fully redundancy. 1730 // 1731 // If all of the instructions we depend on produce a known value for this 1732 // load, then it is fully redundant and we can use PHI insertion to compute 1733 // its value. Insert PHIs and remove the fully redundant value now. 1734 if (UnavailableBlocks.empty()) { 1735 DEBUG(dbgs() << "GVN REMOVING NONLOCAL LOAD: " << *LI << '\n'); 1736 1737 // Perform PHI construction. 1738 Value *V = ConstructSSAForLoadSet(LI, ValuesPerBlock, *this); 1739 LI->replaceAllUsesWith(V); 1740 1741 if (isa<PHINode>(V)) 1742 V->takeName(LI); 1743 if (V->getType()->getScalarType()->isPointerTy()) 1744 MD->invalidateCachedPointerInfo(V); 1745 markInstructionForDeletion(LI); 1746 ++NumGVNLoad; 1747 return true; 1748 } 1749 1750 // Step 4: Eliminate partial redundancy. 1751 if (!EnablePRE || !EnableLoadPRE) 1752 return false; 1753 1754 return PerformLoadPRE(LI, ValuesPerBlock, UnavailableBlocks); 1755} 1756 1757 1758static void patchReplacementInstruction(Instruction *I, Value *Repl) { 1759 // Patch the replacement so that it is not more restrictive than the value 1760 // being replaced. 1761 BinaryOperator *Op = dyn_cast<BinaryOperator>(I); 1762 BinaryOperator *ReplOp = dyn_cast<BinaryOperator>(Repl); 1763 if (Op && ReplOp && isa<OverflowingBinaryOperator>(Op) && 1764 isa<OverflowingBinaryOperator>(ReplOp)) { 1765 if (ReplOp->hasNoSignedWrap() && !Op->hasNoSignedWrap()) 1766 ReplOp->setHasNoSignedWrap(false); 1767 if (ReplOp->hasNoUnsignedWrap() && !Op->hasNoUnsignedWrap()) 1768 ReplOp->setHasNoUnsignedWrap(false); 1769 } 1770 if (Instruction *ReplInst = dyn_cast<Instruction>(Repl)) { 1771 SmallVector<std::pair<unsigned, MDNode*>, 4> Metadata; 1772 ReplInst->getAllMetadataOtherThanDebugLoc(Metadata); 1773 for (int i = 0, n = Metadata.size(); i < n; ++i) { 1774 unsigned Kind = Metadata[i].first; 1775 MDNode *IMD = I->getMetadata(Kind); 1776 MDNode *ReplMD = Metadata[i].second; 1777 switch(Kind) { 1778 default: 1779 ReplInst->setMetadata(Kind, NULL); // Remove unknown metadata 1780 break; 1781 case LLVMContext::MD_dbg: 1782 llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg"); 1783 case LLVMContext::MD_tbaa: 1784 ReplInst->setMetadata(Kind, MDNode::getMostGenericTBAA(IMD, ReplMD)); 1785 break; 1786 case LLVMContext::MD_range: 1787 ReplInst->setMetadata(Kind, MDNode::getMostGenericRange(IMD, ReplMD)); 1788 break; 1789 case LLVMContext::MD_prof: 1790 llvm_unreachable("MD_prof in a non terminator instruction"); 1791 break; 1792 case LLVMContext::MD_fpmath: 1793 ReplInst->setMetadata(Kind, MDNode::getMostGenericFPMath(IMD, ReplMD)); 1794 break; 1795 } 1796 } 1797 } 1798} 1799 1800static void patchAndReplaceAllUsesWith(Instruction *I, Value *Repl) { 1801 patchReplacementInstruction(I, Repl); 1802 I->replaceAllUsesWith(Repl); 1803} 1804 1805/// processLoad - Attempt to eliminate a load, first by eliminating it 1806/// locally, and then attempting non-local elimination if that fails. 1807bool GVN::processLoad(LoadInst *L) { 1808 if (!MD) 1809 return false; 1810 1811 if (!L->isSimple()) 1812 return false; 1813 1814 if (L->use_empty()) { 1815 markInstructionForDeletion(L); 1816 return true; 1817 } 1818 1819 // ... to a pointer that has been loaded from before... 1820 MemDepResult Dep = MD->getDependency(L); 1821 1822 // If we have a clobber and target data is around, see if this is a clobber 1823 // that we can fix up through code synthesis. 1824 if (Dep.isClobber() && TD) { 1825 // Check to see if we have something like this: 1826 // store i32 123, i32* %P 1827 // %A = bitcast i32* %P to i8* 1828 // %B = gep i8* %A, i32 1 1829 // %C = load i8* %B 1830 // 1831 // We could do that by recognizing if the clobber instructions are obviously 1832 // a common base + constant offset, and if the previous store (or memset) 1833 // completely covers this load. This sort of thing can happen in bitfield 1834 // access code. 1835 Value *AvailVal = 0; 1836 if (StoreInst *DepSI = dyn_cast<StoreInst>(Dep.getInst())) { 1837 int Offset = AnalyzeLoadFromClobberingStore(L->getType(), 1838 L->getPointerOperand(), 1839 DepSI, *TD); 1840 if (Offset != -1) 1841 AvailVal = GetStoreValueForLoad(DepSI->getValueOperand(), Offset, 1842 L->getType(), L, *TD); 1843 } 1844 1845 // Check to see if we have something like this: 1846 // load i32* P 1847 // load i8* (P+1) 1848 // if we have this, replace the later with an extraction from the former. 1849 if (LoadInst *DepLI = dyn_cast<LoadInst>(Dep.getInst())) { 1850 // If this is a clobber and L is the first instruction in its block, then 1851 // we have the first instruction in the entry block. 1852 if (DepLI == L) 1853 return false; 1854 1855 int Offset = AnalyzeLoadFromClobberingLoad(L->getType(), 1856 L->getPointerOperand(), 1857 DepLI, *TD); 1858 if (Offset != -1) 1859 AvailVal = GetLoadValueForLoad(DepLI, Offset, L->getType(), L, *this); 1860 } 1861 1862 // If the clobbering value is a memset/memcpy/memmove, see if we can forward 1863 // a value on from it. 1864 if (MemIntrinsic *DepMI = dyn_cast<MemIntrinsic>(Dep.getInst())) { 1865 int Offset = AnalyzeLoadFromClobberingMemInst(L->getType(), 1866 L->getPointerOperand(), 1867 DepMI, *TD); 1868 if (Offset != -1) 1869 AvailVal = GetMemInstValueForLoad(DepMI, Offset, L->getType(), L, *TD); 1870 } 1871 1872 if (AvailVal) { 1873 DEBUG(dbgs() << "GVN COERCED INST:\n" << *Dep.getInst() << '\n' 1874 << *AvailVal << '\n' << *L << "\n\n\n"); 1875 1876 // Replace the load! 1877 L->replaceAllUsesWith(AvailVal); 1878 if (AvailVal->getType()->getScalarType()->isPointerTy()) 1879 MD->invalidateCachedPointerInfo(AvailVal); 1880 markInstructionForDeletion(L); 1881 ++NumGVNLoad; 1882 return true; 1883 } 1884 } 1885 1886 // If the value isn't available, don't do anything! 1887 if (Dep.isClobber()) { 1888 DEBUG( 1889 // fast print dep, using operator<< on instruction is too slow. 1890 dbgs() << "GVN: load "; 1891 WriteAsOperand(dbgs(), L); 1892 Instruction *I = Dep.getInst(); 1893 dbgs() << " is clobbered by " << *I << '\n'; 1894 ); 1895 return false; 1896 } 1897 1898 // If it is defined in another block, try harder. 1899 if (Dep.isNonLocal()) 1900 return processNonLocalLoad(L); 1901 1902 if (!Dep.isDef()) { 1903 DEBUG( 1904 // fast print dep, using operator<< on instruction is too slow. 1905 dbgs() << "GVN: load "; 1906 WriteAsOperand(dbgs(), L); 1907 dbgs() << " has unknown dependence\n"; 1908 ); 1909 return false; 1910 } 1911 1912 Instruction *DepInst = Dep.getInst(); 1913 if (StoreInst *DepSI = dyn_cast<StoreInst>(DepInst)) { 1914 Value *StoredVal = DepSI->getValueOperand(); 1915 1916 // The store and load are to a must-aliased pointer, but they may not 1917 // actually have the same type. See if we know how to reuse the stored 1918 // value (depending on its type). 1919 if (StoredVal->getType() != L->getType()) { 1920 if (TD) { 1921 StoredVal = CoerceAvailableValueToLoadType(StoredVal, L->getType(), 1922 L, *TD); 1923 if (StoredVal == 0) 1924 return false; 1925 1926 DEBUG(dbgs() << "GVN COERCED STORE:\n" << *DepSI << '\n' << *StoredVal 1927 << '\n' << *L << "\n\n\n"); 1928 } 1929 else 1930 return false; 1931 } 1932 1933 // Remove it! 1934 L->replaceAllUsesWith(StoredVal); 1935 if (StoredVal->getType()->getScalarType()->isPointerTy()) 1936 MD->invalidateCachedPointerInfo(StoredVal); 1937 markInstructionForDeletion(L); 1938 ++NumGVNLoad; 1939 return true; 1940 } 1941 1942 if (LoadInst *DepLI = dyn_cast<LoadInst>(DepInst)) { 1943 Value *AvailableVal = DepLI; 1944 1945 // The loads are of a must-aliased pointer, but they may not actually have 1946 // the same type. See if we know how to reuse the previously loaded value 1947 // (depending on its type). 1948 if (DepLI->getType() != L->getType()) { 1949 if (TD) { 1950 AvailableVal = CoerceAvailableValueToLoadType(DepLI, L->getType(), 1951 L, *TD); 1952 if (AvailableVal == 0) 1953 return false; 1954 1955 DEBUG(dbgs() << "GVN COERCED LOAD:\n" << *DepLI << "\n" << *AvailableVal 1956 << "\n" << *L << "\n\n\n"); 1957 } 1958 else 1959 return false; 1960 } 1961 1962 // Remove it! 1963 patchAndReplaceAllUsesWith(L, AvailableVal); 1964 if (DepLI->getType()->getScalarType()->isPointerTy()) 1965 MD->invalidateCachedPointerInfo(DepLI); 1966 markInstructionForDeletion(L); 1967 ++NumGVNLoad; 1968 return true; 1969 } 1970 1971 // If this load really doesn't depend on anything, then we must be loading an 1972 // undef value. This can happen when loading for a fresh allocation with no 1973 // intervening stores, for example. 1974 if (isa<AllocaInst>(DepInst) || isMallocLikeFn(DepInst, TLI)) { 1975 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1976 markInstructionForDeletion(L); 1977 ++NumGVNLoad; 1978 return true; 1979 } 1980 1981 // If this load occurs either right after a lifetime begin, 1982 // then the loaded value is undefined. 1983 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(DepInst)) { 1984 if (II->getIntrinsicID() == Intrinsic::lifetime_start) { 1985 L->replaceAllUsesWith(UndefValue::get(L->getType())); 1986 markInstructionForDeletion(L); 1987 ++NumGVNLoad; 1988 return true; 1989 } 1990 } 1991 1992 return false; 1993} 1994 1995// findLeader - In order to find a leader for a given value number at a 1996// specific basic block, we first obtain the list of all Values for that number, 1997// and then scan the list to find one whose block dominates the block in 1998// question. This is fast because dominator tree queries consist of only 1999// a few comparisons of DFS numbers. 2000Value *GVN::findLeader(const BasicBlock *BB, uint32_t num) { 2001 LeaderTableEntry Vals = LeaderTable[num]; 2002 if (!Vals.Val) return 0; 2003 2004 Value *Val = 0; 2005 if (DT->dominates(Vals.BB, BB)) { 2006 Val = Vals.Val; 2007 if (isa<Constant>(Val)) return Val; 2008 } 2009 2010 LeaderTableEntry* Next = Vals.Next; 2011 while (Next) { 2012 if (DT->dominates(Next->BB, BB)) { 2013 if (isa<Constant>(Next->Val)) return Next->Val; 2014 if (!Val) Val = Next->Val; 2015 } 2016 2017 Next = Next->Next; 2018 } 2019 2020 return Val; 2021} 2022 2023/// replaceAllDominatedUsesWith - Replace all uses of 'From' with 'To' if the 2024/// use is dominated by the given basic block. Returns the number of uses that 2025/// were replaced. 2026unsigned GVN::replaceAllDominatedUsesWith(Value *From, Value *To, 2027 const BasicBlockEdge &Root) { 2028 unsigned Count = 0; 2029 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end(); 2030 UI != UE; ) { 2031 Use &U = (UI++).getUse(); 2032 2033 if (DT->dominates(Root, U)) { 2034 U.set(To); 2035 ++Count; 2036 } 2037 } 2038 return Count; 2039} 2040 2041/// isOnlyReachableViaThisEdge - There is an edge from 'Src' to 'Dst'. Return 2042/// true if every path from the entry block to 'Dst' passes via this edge. In 2043/// particular 'Dst' must not be reachable via another edge from 'Src'. 2044static bool isOnlyReachableViaThisEdge(const BasicBlockEdge &E, 2045 DominatorTree *DT) { 2046 // While in theory it is interesting to consider the case in which Dst has 2047 // more than one predecessor, because Dst might be part of a loop which is 2048 // only reachable from Src, in practice it is pointless since at the time 2049 // GVN runs all such loops have preheaders, which means that Dst will have 2050 // been changed to have only one predecessor, namely Src. 2051 const BasicBlock *Pred = E.getEnd()->getSinglePredecessor(); 2052 const BasicBlock *Src = E.getStart(); 2053 assert((!Pred || Pred == Src) && "No edge between these basic blocks!"); 2054 (void)Src; 2055 return Pred != 0; 2056} 2057 2058/// propagateEquality - The given values are known to be equal in every block 2059/// dominated by 'Root'. Exploit this, for example by replacing 'LHS' with 2060/// 'RHS' everywhere in the scope. Returns whether a change was made. 2061bool GVN::propagateEquality(Value *LHS, Value *RHS, 2062 const BasicBlockEdge &Root) { 2063 SmallVector<std::pair<Value*, Value*>, 4> Worklist; 2064 Worklist.push_back(std::make_pair(LHS, RHS)); 2065 bool Changed = false; 2066 // For speed, compute a conservative fast approximation to 2067 // DT->dominates(Root, Root.getEnd()); 2068 bool RootDominatesEnd = isOnlyReachableViaThisEdge(Root, DT); 2069 2070 while (!Worklist.empty()) { 2071 std::pair<Value*, Value*> Item = Worklist.pop_back_val(); 2072 LHS = Item.first; RHS = Item.second; 2073 2074 if (LHS == RHS) continue; 2075 assert(LHS->getType() == RHS->getType() && "Equality but unequal types!"); 2076 2077 // Don't try to propagate equalities between constants. 2078 if (isa<Constant>(LHS) && isa<Constant>(RHS)) continue; 2079 2080 // Prefer a constant on the right-hand side, or an Argument if no constants. 2081 if (isa<Constant>(LHS) || (isa<Argument>(LHS) && !isa<Constant>(RHS))) 2082 std::swap(LHS, RHS); 2083 assert((isa<Argument>(LHS) || isa<Instruction>(LHS)) && "Unexpected value!"); 2084 2085 // If there is no obvious reason to prefer the left-hand side over the right- 2086 // hand side, ensure the longest lived term is on the right-hand side, so the 2087 // shortest lived term will be replaced by the longest lived. This tends to 2088 // expose more simplifications. 2089 uint32_t LVN = VN.lookup_or_add(LHS); 2090 if ((isa<Argument>(LHS) && isa<Argument>(RHS)) || 2091 (isa<Instruction>(LHS) && isa<Instruction>(RHS))) { 2092 // Move the 'oldest' value to the right-hand side, using the value number as 2093 // a proxy for age. 2094 uint32_t RVN = VN.lookup_or_add(RHS); 2095 if (LVN < RVN) { 2096 std::swap(LHS, RHS); 2097 LVN = RVN; 2098 } 2099 } 2100 2101 // If value numbering later sees that an instruction in the scope is equal 2102 // to 'LHS' then ensure it will be turned into 'RHS'. In order to preserve 2103 // the invariant that instructions only occur in the leader table for their 2104 // own value number (this is used by removeFromLeaderTable), do not do this 2105 // if RHS is an instruction (if an instruction in the scope is morphed into 2106 // LHS then it will be turned into RHS by the next GVN iteration anyway, so 2107 // using the leader table is about compiling faster, not optimizing better). 2108 // The leader table only tracks basic blocks, not edges. Only add to if we 2109 // have the simple case where the edge dominates the end. 2110 if (RootDominatesEnd && !isa<Instruction>(RHS)) 2111 addToLeaderTable(LVN, RHS, Root.getEnd()); 2112 2113 // Replace all occurrences of 'LHS' with 'RHS' everywhere in the scope. As 2114 // LHS always has at least one use that is not dominated by Root, this will 2115 // never do anything if LHS has only one use. 2116 if (!LHS->hasOneUse()) { 2117 unsigned NumReplacements = replaceAllDominatedUsesWith(LHS, RHS, Root); 2118 Changed |= NumReplacements > 0; 2119 NumGVNEqProp += NumReplacements; 2120 } 2121 2122 // Now try to deduce additional equalities from this one. For example, if the 2123 // known equality was "(A != B)" == "false" then it follows that A and B are 2124 // equal in the scope. Only boolean equalities with an explicit true or false 2125 // RHS are currently supported. 2126 if (!RHS->getType()->isIntegerTy(1)) 2127 // Not a boolean equality - bail out. 2128 continue; 2129 ConstantInt *CI = dyn_cast<ConstantInt>(RHS); 2130 if (!CI) 2131 // RHS neither 'true' nor 'false' - bail out. 2132 continue; 2133 // Whether RHS equals 'true'. Otherwise it equals 'false'. 2134 bool isKnownTrue = CI->isAllOnesValue(); 2135 bool isKnownFalse = !isKnownTrue; 2136 2137 // If "A && B" is known true then both A and B are known true. If "A || B" 2138 // is known false then both A and B are known false. 2139 Value *A, *B; 2140 if ((isKnownTrue && match(LHS, m_And(m_Value(A), m_Value(B)))) || 2141 (isKnownFalse && match(LHS, m_Or(m_Value(A), m_Value(B))))) { 2142 Worklist.push_back(std::make_pair(A, RHS)); 2143 Worklist.push_back(std::make_pair(B, RHS)); 2144 continue; 2145 } 2146 2147 // If we are propagating an equality like "(A == B)" == "true" then also 2148 // propagate the equality A == B. When propagating a comparison such as 2149 // "(A >= B)" == "true", replace all instances of "A < B" with "false". 2150 if (ICmpInst *Cmp = dyn_cast<ICmpInst>(LHS)) { 2151 Value *Op0 = Cmp->getOperand(0), *Op1 = Cmp->getOperand(1); 2152 2153 // If "A == B" is known true, or "A != B" is known false, then replace 2154 // A with B everywhere in the scope. 2155 if ((isKnownTrue && Cmp->getPredicate() == CmpInst::ICMP_EQ) || 2156 (isKnownFalse && Cmp->getPredicate() == CmpInst::ICMP_NE)) 2157 Worklist.push_back(std::make_pair(Op0, Op1)); 2158 2159 // If "A >= B" is known true, replace "A < B" with false everywhere. 2160 CmpInst::Predicate NotPred = Cmp->getInversePredicate(); 2161 Constant *NotVal = ConstantInt::get(Cmp->getType(), isKnownFalse); 2162 // Since we don't have the instruction "A < B" immediately to hand, work out 2163 // the value number that it would have and use that to find an appropriate 2164 // instruction (if any). 2165 uint32_t NextNum = VN.getNextUnusedValueNumber(); 2166 uint32_t Num = VN.lookup_or_add_cmp(Cmp->getOpcode(), NotPred, Op0, Op1); 2167 // If the number we were assigned was brand new then there is no point in 2168 // looking for an instruction realizing it: there cannot be one! 2169 if (Num < NextNum) { 2170 Value *NotCmp = findLeader(Root.getEnd(), Num); 2171 if (NotCmp && isa<Instruction>(NotCmp)) { 2172 unsigned NumReplacements = 2173 replaceAllDominatedUsesWith(NotCmp, NotVal, Root); 2174 Changed |= NumReplacements > 0; 2175 NumGVNEqProp += NumReplacements; 2176 } 2177 } 2178 // Ensure that any instruction in scope that gets the "A < B" value number 2179 // is replaced with false. 2180 // The leader table only tracks basic blocks, not edges. Only add to if we 2181 // have the simple case where the edge dominates the end. 2182 if (RootDominatesEnd) 2183 addToLeaderTable(Num, NotVal, Root.getEnd()); 2184 2185 continue; 2186 } 2187 } 2188 2189 return Changed; 2190} 2191 2192/// processInstruction - When calculating availability, handle an instruction 2193/// by inserting it into the appropriate sets 2194bool GVN::processInstruction(Instruction *I) { 2195 // Ignore dbg info intrinsics. 2196 if (isa<DbgInfoIntrinsic>(I)) 2197 return false; 2198 2199 // If the instruction can be easily simplified then do so now in preference 2200 // to value numbering it. Value numbering often exposes redundancies, for 2201 // example if it determines that %y is equal to %x then the instruction 2202 // "%z = and i32 %x, %y" becomes "%z = and i32 %x, %x" which we now simplify. 2203 if (Value *V = SimplifyInstruction(I, TD, TLI, DT)) { 2204 I->replaceAllUsesWith(V); 2205 if (MD && V->getType()->getScalarType()->isPointerTy()) 2206 MD->invalidateCachedPointerInfo(V); 2207 markInstructionForDeletion(I); 2208 ++NumGVNSimpl; 2209 return true; 2210 } 2211 2212 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 2213 if (processLoad(LI)) 2214 return true; 2215 2216 unsigned Num = VN.lookup_or_add(LI); 2217 addToLeaderTable(Num, LI, LI->getParent()); 2218 return false; 2219 } 2220 2221 // For conditional branches, we can perform simple conditional propagation on 2222 // the condition value itself. 2223 if (BranchInst *BI = dyn_cast<BranchInst>(I)) { 2224 if (!BI->isConditional()) 2225 return false; 2226 2227 if (isa<Constant>(BI->getCondition())) 2228 return processFoldableCondBr(BI); 2229 2230 Value *BranchCond = BI->getCondition(); 2231 BasicBlock *TrueSucc = BI->getSuccessor(0); 2232 BasicBlock *FalseSucc = BI->getSuccessor(1); 2233 // Avoid multiple edges early. 2234 if (TrueSucc == FalseSucc) 2235 return false; 2236 2237 BasicBlock *Parent = BI->getParent(); 2238 bool Changed = false; 2239 2240 Value *TrueVal = ConstantInt::getTrue(TrueSucc->getContext()); 2241 BasicBlockEdge TrueE(Parent, TrueSucc); 2242 Changed |= propagateEquality(BranchCond, TrueVal, TrueE); 2243 2244 Value *FalseVal = ConstantInt::getFalse(FalseSucc->getContext()); 2245 BasicBlockEdge FalseE(Parent, FalseSucc); 2246 Changed |= propagateEquality(BranchCond, FalseVal, FalseE); 2247 2248 return Changed; 2249 } 2250 2251 // For switches, propagate the case values into the case destinations. 2252 if (SwitchInst *SI = dyn_cast<SwitchInst>(I)) { 2253 Value *SwitchCond = SI->getCondition(); 2254 BasicBlock *Parent = SI->getParent(); 2255 bool Changed = false; 2256 2257 // Remember how many outgoing edges there are to every successor. 2258 SmallDenseMap<BasicBlock *, unsigned, 16> SwitchEdges; 2259 for (unsigned i = 0, n = SI->getNumSuccessors(); i != n; ++i) 2260 ++SwitchEdges[SI->getSuccessor(i)]; 2261 2262 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end(); 2263 i != e; ++i) { 2264 BasicBlock *Dst = i.getCaseSuccessor(); 2265 // If there is only a single edge, propagate the case value into it. 2266 if (SwitchEdges.lookup(Dst) == 1) { 2267 BasicBlockEdge E(Parent, Dst); 2268 Changed |= propagateEquality(SwitchCond, i.getCaseValue(), E); 2269 } 2270 } 2271 return Changed; 2272 } 2273 2274 // Instructions with void type don't return a value, so there's 2275 // no point in trying to find redundancies in them. 2276 if (I->getType()->isVoidTy()) return false; 2277 2278 uint32_t NextNum = VN.getNextUnusedValueNumber(); 2279 unsigned Num = VN.lookup_or_add(I); 2280 2281 // Allocations are always uniquely numbered, so we can save time and memory 2282 // by fast failing them. 2283 if (isa<AllocaInst>(I) || isa<TerminatorInst>(I) || isa<PHINode>(I)) { 2284 addToLeaderTable(Num, I, I->getParent()); 2285 return false; 2286 } 2287 2288 // If the number we were assigned was a brand new VN, then we don't 2289 // need to do a lookup to see if the number already exists 2290 // somewhere in the domtree: it can't! 2291 if (Num >= NextNum) { 2292 addToLeaderTable(Num, I, I->getParent()); 2293 return false; 2294 } 2295 2296 // Perform fast-path value-number based elimination of values inherited from 2297 // dominators. 2298 Value *repl = findLeader(I->getParent(), Num); 2299 if (repl == 0) { 2300 // Failure, just remember this instance for future use. 2301 addToLeaderTable(Num, I, I->getParent()); 2302 return false; 2303 } 2304 2305 // Remove it! 2306 patchAndReplaceAllUsesWith(I, repl); 2307 if (MD && repl->getType()->getScalarType()->isPointerTy()) 2308 MD->invalidateCachedPointerInfo(repl); 2309 markInstructionForDeletion(I); 2310 return true; 2311} 2312 2313/// runOnFunction - This is the main transformation entry point for a function. 2314bool GVN::runOnFunction(Function& F) { 2315 if (!NoLoads) 2316 MD = &getAnalysis<MemoryDependenceAnalysis>(); 2317 DT = &getAnalysis<DominatorTree>(); 2318 TD = getAnalysisIfAvailable<DataLayout>(); 2319 TLI = &getAnalysis<TargetLibraryInfo>(); 2320 VN.setAliasAnalysis(&getAnalysis<AliasAnalysis>()); 2321 VN.setMemDep(MD); 2322 VN.setDomTree(DT); 2323 2324 bool Changed = false; 2325 bool ShouldContinue = true; 2326 2327 // Merge unconditional branches, allowing PRE to catch more 2328 // optimization opportunities. 2329 for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ) { 2330 BasicBlock *BB = FI++; 2331 2332 bool removedBlock = MergeBlockIntoPredecessor(BB, this); 2333 if (removedBlock) ++NumGVNBlocks; 2334 2335 Changed |= removedBlock; 2336 } 2337 2338 unsigned Iteration = 0; 2339 while (ShouldContinue) { 2340 DEBUG(dbgs() << "GVN iteration: " << Iteration << "\n"); 2341 ShouldContinue = iterateOnFunction(F); 2342 Changed |= ShouldContinue; 2343 ++Iteration; 2344 } 2345 2346 if (EnablePRE) { 2347 // Fabricate val-num for dead-code in order to suppress assertion in 2348 // performPRE(). 2349 assignValNumForDeadCode(); 2350 bool PREChanged = true; 2351 while (PREChanged) { 2352 PREChanged = performPRE(F); 2353 Changed |= PREChanged; 2354 } 2355 } 2356 2357 // FIXME: Should perform GVN again after PRE does something. PRE can move 2358 // computations into blocks where they become fully redundant. Note that 2359 // we can't do this until PRE's critical edge splitting updates memdep. 2360 // Actually, when this happens, we should just fully integrate PRE into GVN. 2361 2362 cleanupGlobalSets(); 2363 // Do not cleanup DeadBlocks in cleanupGlobalSets() as it's called for each 2364 // iteration. 2365 DeadBlocks.clear(); 2366 2367 return Changed; 2368} 2369 2370 2371bool GVN::processBlock(BasicBlock *BB) { 2372 // FIXME: Kill off InstrsToErase by doing erasing eagerly in a helper function 2373 // (and incrementing BI before processing an instruction). 2374 assert(InstrsToErase.empty() && 2375 "We expect InstrsToErase to be empty across iterations"); 2376 if (DeadBlocks.count(BB)) 2377 return false; 2378 2379 bool ChangedFunction = false; 2380 2381 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); 2382 BI != BE;) { 2383 ChangedFunction |= processInstruction(BI); 2384 if (InstrsToErase.empty()) { 2385 ++BI; 2386 continue; 2387 } 2388 2389 // If we need some instructions deleted, do it now. 2390 NumGVNInstr += InstrsToErase.size(); 2391 2392 // Avoid iterator invalidation. 2393 bool AtStart = BI == BB->begin(); 2394 if (!AtStart) 2395 --BI; 2396 2397 for (SmallVectorImpl<Instruction *>::iterator I = InstrsToErase.begin(), 2398 E = InstrsToErase.end(); I != E; ++I) { 2399 DEBUG(dbgs() << "GVN removed: " << **I << '\n'); 2400 if (MD) MD->removeInstruction(*I); 2401 DEBUG(verifyRemoved(*I)); 2402 (*I)->eraseFromParent(); 2403 } 2404 InstrsToErase.clear(); 2405 2406 if (AtStart) 2407 BI = BB->begin(); 2408 else 2409 ++BI; 2410 } 2411 2412 return ChangedFunction; 2413} 2414 2415/// performPRE - Perform a purely local form of PRE that looks for diamond 2416/// control flow patterns and attempts to perform simple PRE at the join point. 2417bool GVN::performPRE(Function &F) { 2418 bool Changed = false; 2419 SmallVector<std::pair<Value*, BasicBlock*>, 8> predMap; 2420 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 2421 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) { 2422 BasicBlock *CurrentBlock = *DI; 2423 2424 // Nothing to PRE in the entry block. 2425 if (CurrentBlock == &F.getEntryBlock()) continue; 2426 2427 // Don't perform PRE on a landing pad. 2428 if (CurrentBlock->isLandingPad()) continue; 2429 2430 for (BasicBlock::iterator BI = CurrentBlock->begin(), 2431 BE = CurrentBlock->end(); BI != BE; ) { 2432 Instruction *CurInst = BI++; 2433 2434 if (isa<AllocaInst>(CurInst) || 2435 isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) || 2436 CurInst->getType()->isVoidTy() || 2437 CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() || 2438 isa<DbgInfoIntrinsic>(CurInst)) 2439 continue; 2440 2441 // Don't do PRE on compares. The PHI would prevent CodeGenPrepare from 2442 // sinking the compare again, and it would force the code generator to 2443 // move the i1 from processor flags or predicate registers into a general 2444 // purpose register. 2445 if (isa<CmpInst>(CurInst)) 2446 continue; 2447 2448 // We don't currently value number ANY inline asm calls. 2449 if (CallInst *CallI = dyn_cast<CallInst>(CurInst)) 2450 if (CallI->isInlineAsm()) 2451 continue; 2452 2453 uint32_t ValNo = VN.lookup(CurInst); 2454 2455 // Look for the predecessors for PRE opportunities. We're 2456 // only trying to solve the basic diamond case, where 2457 // a value is computed in the successor and one predecessor, 2458 // but not the other. We also explicitly disallow cases 2459 // where the successor is its own predecessor, because they're 2460 // more complicated to get right. 2461 unsigned NumWith = 0; 2462 unsigned NumWithout = 0; 2463 BasicBlock *PREPred = 0; 2464 predMap.clear(); 2465 2466 for (pred_iterator PI = pred_begin(CurrentBlock), 2467 PE = pred_end(CurrentBlock); PI != PE; ++PI) { 2468 BasicBlock *P = *PI; 2469 // We're not interested in PRE where the block is its 2470 // own predecessor, or in blocks with predecessors 2471 // that are not reachable. 2472 if (P == CurrentBlock) { 2473 NumWithout = 2; 2474 break; 2475 } else if (!DT->isReachableFromEntry(P)) { 2476 NumWithout = 2; 2477 break; 2478 } 2479 2480 Value* predV = findLeader(P, ValNo); 2481 if (predV == 0) { 2482 predMap.push_back(std::make_pair(static_cast<Value *>(0), P)); 2483 PREPred = P; 2484 ++NumWithout; 2485 } else if (predV == CurInst) { 2486 /* CurInst dominates this predecessor. */ 2487 NumWithout = 2; 2488 break; 2489 } else { 2490 predMap.push_back(std::make_pair(predV, P)); 2491 ++NumWith; 2492 } 2493 } 2494 2495 // Don't do PRE when it might increase code size, i.e. when 2496 // we would need to insert instructions in more than one pred. 2497 if (NumWithout != 1 || NumWith == 0) 2498 continue; 2499 2500 // Don't do PRE across indirect branch. 2501 if (isa<IndirectBrInst>(PREPred->getTerminator())) 2502 continue; 2503 2504 // We can't do PRE safely on a critical edge, so instead we schedule 2505 // the edge to be split and perform the PRE the next time we iterate 2506 // on the function. 2507 unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock); 2508 if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) { 2509 toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum)); 2510 continue; 2511 } 2512 2513 // Instantiate the expression in the predecessor that lacked it. 2514 // Because we are going top-down through the block, all value numbers 2515 // will be available in the predecessor by the time we need them. Any 2516 // that weren't originally present will have been instantiated earlier 2517 // in this loop. 2518 Instruction *PREInstr = CurInst->clone(); 2519 bool success = true; 2520 for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) { 2521 Value *Op = PREInstr->getOperand(i); 2522 if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op)) 2523 continue; 2524 2525 if (Value *V = findLeader(PREPred, VN.lookup(Op))) { 2526 PREInstr->setOperand(i, V); 2527 } else { 2528 success = false; 2529 break; 2530 } 2531 } 2532 2533 // Fail out if we encounter an operand that is not available in 2534 // the PRE predecessor. This is typically because of loads which 2535 // are not value numbered precisely. 2536 if (!success) { 2537 DEBUG(verifyRemoved(PREInstr)); 2538 delete PREInstr; 2539 continue; 2540 } 2541 2542 PREInstr->insertBefore(PREPred->getTerminator()); 2543 PREInstr->setName(CurInst->getName() + ".pre"); 2544 PREInstr->setDebugLoc(CurInst->getDebugLoc()); 2545 VN.add(PREInstr, ValNo); 2546 ++NumGVNPRE; 2547 2548 // Update the availability map to include the new instruction. 2549 addToLeaderTable(ValNo, PREInstr, PREPred); 2550 2551 // Create a PHI to make the value available in this block. 2552 PHINode* Phi = PHINode::Create(CurInst->getType(), predMap.size(), 2553 CurInst->getName() + ".pre-phi", 2554 CurrentBlock->begin()); 2555 for (unsigned i = 0, e = predMap.size(); i != e; ++i) { 2556 if (Value *V = predMap[i].first) 2557 Phi->addIncoming(V, predMap[i].second); 2558 else 2559 Phi->addIncoming(PREInstr, PREPred); 2560 } 2561 2562 VN.add(Phi, ValNo); 2563 addToLeaderTable(ValNo, Phi, CurrentBlock); 2564 Phi->setDebugLoc(CurInst->getDebugLoc()); 2565 CurInst->replaceAllUsesWith(Phi); 2566 if (Phi->getType()->getScalarType()->isPointerTy()) { 2567 // Because we have added a PHI-use of the pointer value, it has now 2568 // "escaped" from alias analysis' perspective. We need to inform 2569 // AA of this. 2570 for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee; 2571 ++ii) { 2572 unsigned jj = PHINode::getOperandNumForIncomingValue(ii); 2573 VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj)); 2574 } 2575 2576 if (MD) 2577 MD->invalidateCachedPointerInfo(Phi); 2578 } 2579 VN.erase(CurInst); 2580 removeFromLeaderTable(ValNo, CurInst, CurrentBlock); 2581 2582 DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n'); 2583 if (MD) MD->removeInstruction(CurInst); 2584 DEBUG(verifyRemoved(CurInst)); 2585 CurInst->eraseFromParent(); 2586 Changed = true; 2587 } 2588 } 2589 2590 if (splitCriticalEdges()) 2591 Changed = true; 2592 2593 return Changed; 2594} 2595 2596/// Split the critical edge connecting the given two blocks, and return 2597/// the block inserted to the critical edge. 2598BasicBlock *GVN::splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ) { 2599 BasicBlock *BB = SplitCriticalEdge(Pred, Succ, this); 2600 if (MD) 2601 MD->invalidateCachedPredecessors(); 2602 return BB; 2603} 2604 2605/// splitCriticalEdges - Split critical edges found during the previous 2606/// iteration that may enable further optimization. 2607bool GVN::splitCriticalEdges() { 2608 if (toSplit.empty()) 2609 return false; 2610 do { 2611 std::pair<TerminatorInst*, unsigned> Edge = toSplit.pop_back_val(); 2612 SplitCriticalEdge(Edge.first, Edge.second, this); 2613 } while (!toSplit.empty()); 2614 if (MD) MD->invalidateCachedPredecessors(); 2615 return true; 2616} 2617 2618/// iterateOnFunction - Executes one iteration of GVN 2619bool GVN::iterateOnFunction(Function &F) { 2620 cleanupGlobalSets(); 2621 2622 // Top-down walk of the dominator tree 2623 bool Changed = false; 2624#if 0 2625 // Needed for value numbering with phi construction to work. 2626 ReversePostOrderTraversal<Function*> RPOT(&F); 2627 for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(), 2628 RE = RPOT.end(); RI != RE; ++RI) 2629 Changed |= processBlock(*RI); 2630#else 2631 // Save the blocks this function have before transformation begins. GVN may 2632 // split critical edge, and hence may invalidate the RPO/DT iterator. 2633 // 2634 std::vector<BasicBlock *> BBVect; 2635 BBVect.reserve(256); 2636 for (df_iterator<DomTreeNode*> DI = df_begin(DT->getRootNode()), 2637 DE = df_end(DT->getRootNode()); DI != DE; ++DI) 2638 BBVect.push_back(DI->getBlock()); 2639 2640 for (std::vector<BasicBlock *>::iterator I = BBVect.begin(), E = BBVect.end(); 2641 I != E; I++) 2642 Changed |= processBlock(*I); 2643#endif 2644 2645 return Changed; 2646} 2647 2648void GVN::cleanupGlobalSets() { 2649 VN.clear(); 2650 LeaderTable.clear(); 2651 TableAllocator.Reset(); 2652} 2653 2654/// verifyRemoved - Verify that the specified instruction does not occur in our 2655/// internal data structures. 2656void GVN::verifyRemoved(const Instruction *Inst) const { 2657 VN.verifyRemoved(Inst); 2658 2659 // Walk through the value number scope to make sure the instruction isn't 2660 // ferreted away in it. 2661 for (DenseMap<uint32_t, LeaderTableEntry>::const_iterator 2662 I = LeaderTable.begin(), E = LeaderTable.end(); I != E; ++I) { 2663 const LeaderTableEntry *Node = &I->second; 2664 assert(Node->Val != Inst && "Inst still in value numbering scope!"); 2665 2666 while (Node->Next) { 2667 Node = Node->Next; 2668 assert(Node->Val != Inst && "Inst still in value numbering scope!"); 2669 } 2670 } 2671} 2672 2673// BB is declared dead, which implied other blocks become dead as well. This 2674// function is to add all these blocks to "DeadBlocks". For the dead blocks' 2675// live successors, update their phi nodes by replacing the operands 2676// corresponding to dead blocks with UndefVal. 2677// 2678void GVN::addDeadBlock(BasicBlock *BB) { 2679 SmallVector<BasicBlock *, 4> NewDead; 2680 SmallSetVector<BasicBlock *, 4> DF; 2681 2682 NewDead.push_back(BB); 2683 while (!NewDead.empty()) { 2684 BasicBlock *D = NewDead.pop_back_val(); 2685 if (DeadBlocks.count(D)) 2686 continue; 2687 2688 // All blocks dominated by D are dead. 2689 SmallVector<BasicBlock *, 8> Dom; 2690 DT->getDescendants(D, Dom); 2691 DeadBlocks.insert(Dom.begin(), Dom.end()); 2692 2693 // Figure out the dominance-frontier(D). 2694 for (SmallVectorImpl<BasicBlock *>::iterator I = Dom.begin(), 2695 E = Dom.end(); I != E; I++) { 2696 BasicBlock *B = *I; 2697 for (succ_iterator SI = succ_begin(B), SE = succ_end(B); SI != SE; SI++) { 2698 BasicBlock *S = *SI; 2699 if (DeadBlocks.count(S)) 2700 continue; 2701 2702 bool AllPredDead = true; 2703 for (pred_iterator PI = pred_begin(S), PE = pred_end(S); PI != PE; PI++) 2704 if (!DeadBlocks.count(*PI)) { 2705 AllPredDead = false; 2706 break; 2707 } 2708 2709 if (!AllPredDead) { 2710 // S could be proved dead later on. That is why we don't update phi 2711 // operands at this moment. 2712 DF.insert(S); 2713 } else { 2714 // While S is not dominated by D, it is dead by now. This could take 2715 // place if S already have a dead predecessor before D is declared 2716 // dead. 2717 NewDead.push_back(S); 2718 } 2719 } 2720 } 2721 } 2722 2723 // For the dead blocks' live successors, update their phi nodes by replacing 2724 // the operands corresponding to dead blocks with UndefVal. 2725 for(SmallSetVector<BasicBlock *, 4>::iterator I = DF.begin(), E = DF.end(); 2726 I != E; I++) { 2727 BasicBlock *B = *I; 2728 if (DeadBlocks.count(B)) 2729 continue; 2730 2731 for (pred_iterator PI = pred_begin(B), PE = pred_end(B); PI != PE; PI++) { 2732 BasicBlock *P = *PI; 2733 if (!DeadBlocks.count(P)) 2734 continue; 2735 for (BasicBlock::iterator II = B->begin(); isa<PHINode>(II); ++II) { 2736 PHINode &Phi = cast<PHINode>(*II); 2737 Phi.setIncomingValue(Phi.getBasicBlockIndex(P), 2738 UndefValue::get(Phi.getType())); 2739 } 2740 } 2741 } 2742} 2743 2744// If the given branch is recognized as a foldable branch (i.e. conditional 2745// branch with constant condition), it will perform following analyses and 2746// transformation. 2747// 1) If the dead out-coming edge is a critical-edge, split it. Let 2748// R be the target of the dead out-coming edge. 2749// 1) Identify the set of dead blocks implied by the branch's dead outcoming 2750// edge. The result of this step will be {X| X is dominated by R} 2751// 2) Identify those blocks which haves at least one dead prodecessor. The 2752// result of this step will be dominance-frontier(R). 2753// 3) Update the PHIs in DF(R) by replacing the operands corresponding to 2754// dead blocks with "UndefVal" in an hope these PHIs will optimized away. 2755// 2756// Return true iff *NEW* dead code are found. 2757bool GVN::processFoldableCondBr(BranchInst *BI) { 2758 if (!BI || BI->isUnconditional()) 2759 return false; 2760 2761 ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition()); 2762 if (!Cond) 2763 return false; 2764 2765 BasicBlock *DeadRoot = Cond->getZExtValue() ? 2766 BI->getSuccessor(1) : BI->getSuccessor(0); 2767 if (DeadBlocks.count(DeadRoot)) 2768 return false; 2769 2770 if (!DeadRoot->getSinglePredecessor()) 2771 DeadRoot = splitCriticalEdges(BI->getParent(), DeadRoot); 2772 2773 addDeadBlock(DeadRoot); 2774 return true; 2775} 2776 2777// performPRE() will trigger assert if it come across an instruciton without 2778// associated val-num. As it normally has far more live instructions than dead 2779// instructions, it makes more sense just to "fabricate" a val-number for the 2780// dead code than checking if instruction involved is dead or not. 2781void GVN::assignValNumForDeadCode() { 2782 for (SetVector<BasicBlock *>::iterator I = DeadBlocks.begin(), 2783 E = DeadBlocks.end(); I != E; I++) { 2784 BasicBlock *BB = *I; 2785 for (BasicBlock::iterator II = BB->begin(), EE = BB->end(); 2786 II != EE; II++) { 2787 Instruction *Inst = &*II; 2788 unsigned ValNum = VN.lookup_or_add(Inst); 2789 addToLeaderTable(ValNum, Inst, BB); 2790 } 2791 } 2792} 2793