IndVarSimplify.cpp revision fd93908ae8b9684fe71c239e3c6cfe13ff6a2663
1//===- IndVarSimplify.cpp - Induction Variable Elimination ----------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file was developed by the LLVM research group and is distributed under 6// the University of Illinois Open Source License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This transformation analyzes and transforms the induction variables (and 11// computations derived from them) into simpler forms suitable for subsequent 12// analysis and transformation. 13// 14// This transformation make the following changes to each loop with an 15// identifiable induction variable: 16// 1. All loops are transformed to have a SINGLE canonical induction variable 17// which starts at zero and steps by one. 18// 2. The canonical induction variable is guaranteed to be the first PHI node 19// in the loop header block. 20// 3. Any pointer arithmetic recurrences are raised to use array subscripts. 21// 22// If the trip count of a loop is computable, this pass also makes the following 23// changes: 24// 1. The exit condition for the loop is canonicalized to compare the 25// induction value against the exit value. This turns loops like: 26// 'for (i = 7; i*i < 1000; ++i)' into 'for (i = 0; i != 25; ++i)' 27// 2. Any use outside of the loop of an expression derived from the indvar 28// is changed to compute the derived value outside of the loop, eliminating 29// the dependence on the exit value of the induction variable. If the only 30// purpose of the loop is to compute the exit value of some derived 31// expression, this transformation will make the loop dead. 32// 33// This transformation should be followed by strength reduction after all of the 34// desired loop transformations have been performed. Additionally, on targets 35// where it is profitable, the loop could be transformed to count down to zero 36// (the "do loop" optimization). 37// 38//===----------------------------------------------------------------------===// 39 40#include "llvm/Transforms/Scalar.h" 41#include "llvm/BasicBlock.h" 42#include "llvm/Constants.h" 43#include "llvm/Instructions.h" 44#include "llvm/Type.h" 45#include "llvm/Analysis/ScalarEvolutionExpressions.h" 46#include "llvm/Analysis/LoopInfo.h" 47#include "llvm/Support/CFG.h" 48#include "llvm/Support/GetElementPtrTypeIterator.h" 49#include "llvm/Transforms/Utils/Local.h" 50#include "llvm/Support/CommandLine.h" 51#include "llvm/ADT/Statistic.h" 52using namespace llvm; 53 54namespace { 55 /// SCEVExpander - This class uses information about analyze scalars to 56 /// rewrite expressions in canonical form. 57 /// 58 /// Clients should create an instance of this class when rewriting is needed, 59 /// and destroying it when finished to allow the release of the associated 60 /// memory. 61 struct SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> { 62 ScalarEvolution &SE; 63 LoopInfo &LI; 64 std::map<SCEVHandle, Value*> InsertedExpressions; 65 std::set<Instruction*> InsertedInstructions; 66 67 Instruction *InsertPt; 68 69 friend struct SCEVVisitor<SCEVExpander, Value*>; 70 public: 71 SCEVExpander(ScalarEvolution &se, LoopInfo &li) : SE(se), LI(li) {} 72 73 /// isInsertedInstruction - Return true if the specified instruction was 74 /// inserted by the code rewriter. If so, the client should not modify the 75 /// instruction. 76 bool isInsertedInstruction(Instruction *I) const { 77 return InsertedInstructions.count(I); 78 } 79 80 /// getOrInsertCanonicalInductionVariable - This method returns the 81 /// canonical induction variable of the specified type for the specified 82 /// loop (inserting one if there is none). A canonical induction variable 83 /// starts at zero and steps by one on each iteration. 84 Value *getOrInsertCanonicalInductionVariable(const Loop *L, const Type *Ty){ 85 assert((Ty->isInteger() || Ty->isFloatingPoint()) && 86 "Can only insert integer or floating point induction variables!"); 87 SCEVHandle H = SCEVAddRecExpr::get(SCEVUnknown::getIntegerSCEV(0, Ty), 88 SCEVUnknown::getIntegerSCEV(1, Ty), L); 89 return expand(H); 90 } 91 92 /// addInsertedValue - Remember the specified instruction as being the 93 /// canonical form for the specified SCEV. 94 void addInsertedValue(Instruction *I, SCEV *S) { 95 InsertedExpressions[S] = (Value*)I; 96 InsertedInstructions.insert(I); 97 } 98 99 /// expandCodeFor - Insert code to directly compute the specified SCEV 100 /// expression into the program. The inserted code is inserted into the 101 /// specified block. 102 /// 103 /// If a particular value sign is required, a type may be specified for the 104 /// result. 105 Value *expandCodeFor(SCEVHandle SH, Instruction *IP, const Type *Ty = 0) { 106 // Expand the code for this SCEV. 107 this->InsertPt = IP; 108 return expandInTy(SH, Ty); 109 } 110 111 protected: 112 Value *expand(SCEV *S) { 113 // Check to see if we already expanded this. 114 std::map<SCEVHandle, Value*>::iterator I = InsertedExpressions.find(S); 115 if (I != InsertedExpressions.end()) 116 return I->second; 117 118 Value *V = visit(S); 119 InsertedExpressions[S] = V; 120 return V; 121 } 122 123 Value *expandInTy(SCEV *S, const Type *Ty) { 124 Value *V = expand(S); 125 if (Ty && V->getType() != Ty) { 126 // FIXME: keep track of the cast instruction. 127 if (Constant *C = dyn_cast<Constant>(V)) 128 return ConstantExpr::getCast(C, Ty); 129 else if (Instruction *I = dyn_cast<Instruction>(V)) { 130 // Check to see if there is already a cast. If there is, use it. 131 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 132 UI != E; ++UI) { 133 if ((*UI)->getType() == Ty) 134 if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI))) { 135 BasicBlock::iterator It = I; ++It; 136 if (isa<InvokeInst>(I)) 137 It = cast<InvokeInst>(I)->getNormalDest()->begin(); 138 while (isa<PHINode>(It)) ++It; 139 if (It != BasicBlock::iterator(CI)) { 140 // Splice the cast immediately after the operand in question. 141 BasicBlock::InstListType &InstList = 142 It->getParent()->getInstList(); 143 InstList.splice(It, CI->getParent()->getInstList(), CI); 144 } 145 return CI; 146 } 147 } 148 BasicBlock::iterator IP = I; ++IP; 149 if (InvokeInst *II = dyn_cast<InvokeInst>(I)) 150 IP = II->getNormalDest()->begin(); 151 while (isa<PHINode>(IP)) ++IP; 152 return new CastInst(V, Ty, V->getName(), IP); 153 } else { 154 // FIXME: check to see if there is already a cast! 155 return new CastInst(V, Ty, V->getName(), InsertPt); 156 } 157 } 158 return V; 159 } 160 161 Value *visitConstant(SCEVConstant *S) { 162 return S->getValue(); 163 } 164 165 Value *visitTruncateExpr(SCEVTruncateExpr *S) { 166 Value *V = expand(S->getOperand()); 167 return new CastInst(V, S->getType(), "tmp.", InsertPt); 168 } 169 170 Value *visitZeroExtendExpr(SCEVZeroExtendExpr *S) { 171 Value *V = expandInTy(S->getOperand(),S->getType()->getUnsignedVersion()); 172 return new CastInst(V, S->getType(), "tmp.", InsertPt); 173 } 174 175 Value *visitAddExpr(SCEVAddExpr *S) { 176 const Type *Ty = S->getType(); 177 Value *V = expandInTy(S->getOperand(S->getNumOperands()-1), Ty); 178 179 // Emit a bunch of add instructions 180 for (int i = S->getNumOperands()-2; i >= 0; --i) 181 V = BinaryOperator::createAdd(V, expandInTy(S->getOperand(i), Ty), 182 "tmp.", InsertPt); 183 return V; 184 } 185 186 Value *visitMulExpr(SCEVMulExpr *S); 187 188 Value *visitUDivExpr(SCEVUDivExpr *S) { 189 const Type *Ty = S->getType(); 190 Value *LHS = expandInTy(S->getLHS(), Ty); 191 Value *RHS = expandInTy(S->getRHS(), Ty); 192 return BinaryOperator::createDiv(LHS, RHS, "tmp.", InsertPt); 193 } 194 195 Value *visitAddRecExpr(SCEVAddRecExpr *S); 196 197 Value *visitUnknown(SCEVUnknown *S) { 198 return S->getValue(); 199 } 200 }; 201} 202 203Value *SCEVExpander::visitMulExpr(SCEVMulExpr *S) { 204 const Type *Ty = S->getType(); 205 int FirstOp = 0; // Set if we should emit a subtract. 206 if (SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0))) 207 if (SC->getValue()->isAllOnesValue()) 208 FirstOp = 1; 209 210 int i = S->getNumOperands()-2; 211 Value *V = expandInTy(S->getOperand(i+1), Ty); 212 213 // Emit a bunch of multiply instructions 214 for (; i >= FirstOp; --i) 215 V = BinaryOperator::createMul(V, expandInTy(S->getOperand(i), Ty), 216 "tmp.", InsertPt); 217 // -1 * ... ---> 0 - ... 218 if (FirstOp == 1) 219 V = BinaryOperator::createNeg(V, "tmp.", InsertPt); 220 return V; 221} 222 223Value *SCEVExpander::visitAddRecExpr(SCEVAddRecExpr *S) { 224 const Type *Ty = S->getType(); 225 const Loop *L = S->getLoop(); 226 // We cannot yet do fp recurrences, e.g. the xform of {X,+,F} --> X+{0,+,F} 227 assert(Ty->isIntegral() && "Cannot expand fp recurrences yet!"); 228 229 // {X,+,F} --> X + {0,+,F} 230 if (!isa<SCEVConstant>(S->getStart()) || 231 !cast<SCEVConstant>(S->getStart())->getValue()->isNullValue()) { 232 Value *Start = expandInTy(S->getStart(), Ty); 233 std::vector<SCEVHandle> NewOps(S->op_begin(), S->op_end()); 234 NewOps[0] = SCEVUnknown::getIntegerSCEV(0, Ty); 235 Value *Rest = expandInTy(SCEVAddRecExpr::get(NewOps, L), Ty); 236 237 // FIXME: look for an existing add to use. 238 return BinaryOperator::createAdd(Rest, Start, "tmp.", InsertPt); 239 } 240 241 // {0,+,1} --> Insert a canonical induction variable into the loop! 242 if (S->getNumOperands() == 2 && 243 S->getOperand(1) == SCEVUnknown::getIntegerSCEV(1, Ty)) { 244 // Create and insert the PHI node for the induction variable in the 245 // specified loop. 246 BasicBlock *Header = L->getHeader(); 247 PHINode *PN = new PHINode(Ty, "indvar", Header->begin()); 248 PN->addIncoming(Constant::getNullValue(Ty), L->getLoopPreheader()); 249 250 pred_iterator HPI = pred_begin(Header); 251 assert(HPI != pred_end(Header) && "Loop with zero preds???"); 252 if (!L->contains(*HPI)) ++HPI; 253 assert(HPI != pred_end(Header) && L->contains(*HPI) && 254 "No backedge in loop?"); 255 256 // Insert a unit add instruction right before the terminator corresponding 257 // to the back-edge. 258 Constant *One = Ty->isFloatingPoint() ? (Constant*)ConstantFP::get(Ty, 1.0) 259 : ConstantInt::get(Ty, 1); 260 Instruction *Add = BinaryOperator::createAdd(PN, One, "indvar.next", 261 (*HPI)->getTerminator()); 262 263 pred_iterator PI = pred_begin(Header); 264 if (*PI == L->getLoopPreheader()) 265 ++PI; 266 PN->addIncoming(Add, *PI); 267 return PN; 268 } 269 270 // Get the canonical induction variable I for this loop. 271 Value *I = getOrInsertCanonicalInductionVariable(L, Ty); 272 273 if (S->getNumOperands() == 2) { // {0,+,F} --> i*F 274 Value *F = expandInTy(S->getOperand(1), Ty); 275 return BinaryOperator::createMul(I, F, "tmp.", InsertPt); 276 } 277 278 // If this is a chain of recurrences, turn it into a closed form, using the 279 // folders, then expandCodeFor the closed form. This allows the folders to 280 // simplify the expression without having to build a bunch of special code 281 // into this folder. 282 SCEVHandle IH = SCEVUnknown::get(I); // Get I as a "symbolic" SCEV. 283 284 SCEVHandle V = S->evaluateAtIteration(IH); 285 //std::cerr << "Evaluated: " << *this << "\n to: " << *V << "\n"; 286 287 return expandInTy(V, Ty); 288} 289 290 291namespace { 292 Statistic<> NumRemoved ("indvars", "Number of aux indvars removed"); 293 Statistic<> NumPointer ("indvars", "Number of pointer indvars promoted"); 294 Statistic<> NumInserted("indvars", "Number of canonical indvars added"); 295 Statistic<> NumReplaced("indvars", "Number of exit values replaced"); 296 Statistic<> NumLFTR ("indvars", "Number of loop exit tests replaced"); 297 298 class IndVarSimplify : public FunctionPass { 299 LoopInfo *LI; 300 ScalarEvolution *SE; 301 bool Changed; 302 public: 303 virtual bool runOnFunction(Function &) { 304 LI = &getAnalysis<LoopInfo>(); 305 SE = &getAnalysis<ScalarEvolution>(); 306 Changed = false; 307 308 // Induction Variables live in the header nodes of loops 309 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I) 310 runOnLoop(*I); 311 return Changed; 312 } 313 314 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 315 AU.addRequiredID(LoopSimplifyID); 316 AU.addRequired<ScalarEvolution>(); 317 AU.addRequired<LoopInfo>(); 318 AU.addPreservedID(LoopSimplifyID); 319 AU.setPreservesCFG(); 320 } 321 private: 322 void runOnLoop(Loop *L); 323 void EliminatePointerRecurrence(PHINode *PN, BasicBlock *Preheader, 324 std::set<Instruction*> &DeadInsts); 325 void LinearFunctionTestReplace(Loop *L, SCEV *IterationCount, 326 SCEVExpander &RW); 327 void RewriteLoopExitValues(Loop *L); 328 329 void DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts); 330 }; 331 RegisterOpt<IndVarSimplify> X("indvars", "Canonicalize Induction Variables"); 332} 333 334FunctionPass *llvm::createIndVarSimplifyPass() { 335 return new IndVarSimplify(); 336} 337 338/// DeleteTriviallyDeadInstructions - If any of the instructions is the 339/// specified set are trivially dead, delete them and see if this makes any of 340/// their operands subsequently dead. 341void IndVarSimplify:: 342DeleteTriviallyDeadInstructions(std::set<Instruction*> &Insts) { 343 while (!Insts.empty()) { 344 Instruction *I = *Insts.begin(); 345 Insts.erase(Insts.begin()); 346 if (isInstructionTriviallyDead(I)) { 347 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) 348 if (Instruction *U = dyn_cast<Instruction>(I->getOperand(i))) 349 Insts.insert(U); 350 SE->deleteInstructionFromRecords(I); 351 I->eraseFromParent(); 352 Changed = true; 353 } 354 } 355} 356 357 358/// EliminatePointerRecurrence - Check to see if this is a trivial GEP pointer 359/// recurrence. If so, change it into an integer recurrence, permitting 360/// analysis by the SCEV routines. 361void IndVarSimplify::EliminatePointerRecurrence(PHINode *PN, 362 BasicBlock *Preheader, 363 std::set<Instruction*> &DeadInsts) { 364 assert(PN->getNumIncomingValues() == 2 && "Noncanonicalized loop!"); 365 unsigned PreheaderIdx = PN->getBasicBlockIndex(Preheader); 366 unsigned BackedgeIdx = PreheaderIdx^1; 367 if (GetElementPtrInst *GEPI = 368 dyn_cast<GetElementPtrInst>(PN->getIncomingValue(BackedgeIdx))) 369 if (GEPI->getOperand(0) == PN) { 370 assert(GEPI->getNumOperands() == 2 && "GEP types must mismatch!"); 371 372 // Okay, we found a pointer recurrence. Transform this pointer 373 // recurrence into an integer recurrence. Compute the value that gets 374 // added to the pointer at every iteration. 375 Value *AddedVal = GEPI->getOperand(1); 376 377 // Insert a new integer PHI node into the top of the block. 378 PHINode *NewPhi = new PHINode(AddedVal->getType(), 379 PN->getName()+".rec", PN); 380 NewPhi->addIncoming(Constant::getNullValue(NewPhi->getType()), Preheader); 381 382 // Create the new add instruction. 383 Value *NewAdd = BinaryOperator::createAdd(NewPhi, AddedVal, 384 GEPI->getName()+".rec", GEPI); 385 NewPhi->addIncoming(NewAdd, PN->getIncomingBlock(BackedgeIdx)); 386 387 // Update the existing GEP to use the recurrence. 388 GEPI->setOperand(0, PN->getIncomingValue(PreheaderIdx)); 389 390 // Update the GEP to use the new recurrence we just inserted. 391 GEPI->setOperand(1, NewAdd); 392 393 // If the incoming value is a constant expr GEP, try peeling out the array 394 // 0 index if possible to make things simpler. 395 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(GEPI->getOperand(0))) 396 if (CE->getOpcode() == Instruction::GetElementPtr) { 397 unsigned NumOps = CE->getNumOperands(); 398 assert(NumOps > 1 && "CE folding didn't work!"); 399 if (CE->getOperand(NumOps-1)->isNullValue()) { 400 // Check to make sure the last index really is an array index. 401 gep_type_iterator GTI = gep_type_begin(GEPI); 402 for (unsigned i = 1, e = GEPI->getNumOperands()-1; 403 i != e; ++i, ++GTI) 404 /*empty*/; 405 if (isa<SequentialType>(*GTI)) { 406 // Pull the last index out of the constant expr GEP. 407 std::vector<Value*> CEIdxs(CE->op_begin()+1, CE->op_end()-1); 408 Constant *NCE = ConstantExpr::getGetElementPtr(CE->getOperand(0), 409 CEIdxs); 410 GetElementPtrInst *NGEPI = 411 new GetElementPtrInst(NCE, Constant::getNullValue(Type::IntTy), 412 NewAdd, GEPI->getName(), GEPI); 413 GEPI->replaceAllUsesWith(NGEPI); 414 GEPI->eraseFromParent(); 415 GEPI = NGEPI; 416 } 417 } 418 } 419 420 421 // Finally, if there are any other users of the PHI node, we must 422 // insert a new GEP instruction that uses the pre-incremented version 423 // of the induction amount. 424 if (!PN->use_empty()) { 425 BasicBlock::iterator InsertPos = PN; ++InsertPos; 426 while (isa<PHINode>(InsertPos)) ++InsertPos; 427 std::string Name = PN->getName(); PN->setName(""); 428 Value *PreInc = 429 new GetElementPtrInst(PN->getIncomingValue(PreheaderIdx), 430 std::vector<Value*>(1, NewPhi), Name, 431 InsertPos); 432 PN->replaceAllUsesWith(PreInc); 433 } 434 435 // Delete the old PHI for sure, and the GEP if its otherwise unused. 436 DeadInsts.insert(PN); 437 438 ++NumPointer; 439 Changed = true; 440 } 441} 442 443/// LinearFunctionTestReplace - This method rewrites the exit condition of the 444/// loop to be a canonical != comparison against the incremented loop induction 445/// variable. This pass is able to rewrite the exit tests of any loop where the 446/// SCEV analysis can determine a loop-invariant trip count of the loop, which 447/// is actually a much broader range than just linear tests. 448void IndVarSimplify::LinearFunctionTestReplace(Loop *L, SCEV *IterationCount, 449 SCEVExpander &RW) { 450 // Find the exit block for the loop. We can currently only handle loops with 451 // a single exit. 452 std::vector<BasicBlock*> ExitBlocks; 453 L->getExitBlocks(ExitBlocks); 454 if (ExitBlocks.size() != 1) return; 455 BasicBlock *ExitBlock = ExitBlocks[0]; 456 457 // Make sure there is only one predecessor block in the loop. 458 BasicBlock *ExitingBlock = 0; 459 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock); 460 PI != PE; ++PI) 461 if (L->contains(*PI)) { 462 if (ExitingBlock == 0) 463 ExitingBlock = *PI; 464 else 465 return; // Multiple exits from loop to this block. 466 } 467 assert(ExitingBlock && "Loop info is broken"); 468 469 if (!isa<BranchInst>(ExitingBlock->getTerminator())) 470 return; // Can't rewrite non-branch yet 471 BranchInst *BI = cast<BranchInst>(ExitingBlock->getTerminator()); 472 assert(BI->isConditional() && "Must be conditional to be part of loop!"); 473 474 std::set<Instruction*> InstructionsToDelete; 475 if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition())) 476 InstructionsToDelete.insert(Cond); 477 478 // If the exiting block is not the same as the backedge block, we must compare 479 // against the preincremented value, otherwise we prefer to compare against 480 // the post-incremented value. 481 BasicBlock *Header = L->getHeader(); 482 pred_iterator HPI = pred_begin(Header); 483 assert(HPI != pred_end(Header) && "Loop with zero preds???"); 484 if (!L->contains(*HPI)) ++HPI; 485 assert(HPI != pred_end(Header) && L->contains(*HPI) && 486 "No backedge in loop?"); 487 488 SCEVHandle TripCount = IterationCount; 489 Value *IndVar; 490 if (*HPI == ExitingBlock) { 491 // The IterationCount expression contains the number of times that the 492 // backedge actually branches to the loop header. This is one less than the 493 // number of times the loop executes, so add one to it. 494 Constant *OneC = ConstantInt::get(IterationCount->getType(), 1); 495 TripCount = SCEVAddExpr::get(IterationCount, SCEVUnknown::get(OneC)); 496 IndVar = L->getCanonicalInductionVariableIncrement(); 497 } else { 498 // We have to use the preincremented value... 499 IndVar = L->getCanonicalInductionVariable(); 500 } 501 502 // Expand the code for the iteration count into the preheader of the loop. 503 BasicBlock *Preheader = L->getLoopPreheader(); 504 Value *ExitCnt = RW.expandCodeFor(TripCount, Preheader->getTerminator(), 505 IndVar->getType()); 506 507 // Insert a new setne or seteq instruction before the branch. 508 Instruction::BinaryOps Opcode; 509 if (L->contains(BI->getSuccessor(0))) 510 Opcode = Instruction::SetNE; 511 else 512 Opcode = Instruction::SetEQ; 513 514 Value *Cond = new SetCondInst(Opcode, IndVar, ExitCnt, "exitcond", BI); 515 BI->setCondition(Cond); 516 ++NumLFTR; 517 Changed = true; 518 519 DeleteTriviallyDeadInstructions(InstructionsToDelete); 520} 521 522 523/// RewriteLoopExitValues - Check to see if this loop has a computable 524/// loop-invariant execution count. If so, this means that we can compute the 525/// final value of any expressions that are recurrent in the loop, and 526/// substitute the exit values from the loop into any instructions outside of 527/// the loop that use the final values of the current expressions. 528void IndVarSimplify::RewriteLoopExitValues(Loop *L) { 529 BasicBlock *Preheader = L->getLoopPreheader(); 530 531 // Scan all of the instructions in the loop, looking at those that have 532 // extra-loop users and which are recurrences. 533 SCEVExpander Rewriter(*SE, *LI); 534 535 // We insert the code into the preheader of the loop if the loop contains 536 // multiple exit blocks, or in the exit block if there is exactly one. 537 BasicBlock *BlockToInsertInto; 538 std::vector<BasicBlock*> ExitBlocks; 539 L->getExitBlocks(ExitBlocks); 540 if (ExitBlocks.size() == 1) 541 BlockToInsertInto = ExitBlocks[0]; 542 else 543 BlockToInsertInto = Preheader; 544 BasicBlock::iterator InsertPt = BlockToInsertInto->begin(); 545 while (isa<PHINode>(InsertPt)) ++InsertPt; 546 547 bool HasConstantItCount = isa<SCEVConstant>(SE->getIterationCount(L)); 548 549 std::set<Instruction*> InstructionsToDelete; 550 551 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i) 552 if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop... 553 BasicBlock *BB = L->getBlocks()[i]; 554 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 555 if (I->getType()->isInteger()) { // Is an integer instruction 556 SCEVHandle SH = SE->getSCEV(I); 557 if (SH->hasComputableLoopEvolution(L) || // Varies predictably 558 HasConstantItCount) { 559 // Find out if this predictably varying value is actually used 560 // outside of the loop. "extra" as opposed to "intra". 561 std::vector<User*> ExtraLoopUsers; 562 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); 563 UI != E; ++UI) 564 if (!L->contains(cast<Instruction>(*UI)->getParent())) 565 ExtraLoopUsers.push_back(*UI); 566 if (!ExtraLoopUsers.empty()) { 567 // Okay, this instruction has a user outside of the current loop 568 // and varies predictably in this loop. Evaluate the value it 569 // contains when the loop exits, and insert code for it. 570 SCEVHandle ExitValue = SE->getSCEVAtScope(I, L->getParentLoop()); 571 if (!isa<SCEVCouldNotCompute>(ExitValue)) { 572 Changed = true; 573 ++NumReplaced; 574 Value *NewVal = Rewriter.expandCodeFor(ExitValue, InsertPt, 575 I->getType()); 576 577 // Rewrite any users of the computed value outside of the loop 578 // with the newly computed value. 579 for (unsigned i = 0, e = ExtraLoopUsers.size(); i != e; ++i) 580 ExtraLoopUsers[i]->replaceUsesOfWith(I, NewVal); 581 582 // If this instruction is dead now, schedule it to be removed. 583 if (I->use_empty()) 584 InstructionsToDelete.insert(I); 585 } 586 } 587 } 588 } 589 } 590 591 DeleteTriviallyDeadInstructions(InstructionsToDelete); 592} 593 594 595void IndVarSimplify::runOnLoop(Loop *L) { 596 // First step. Check to see if there are any trivial GEP pointer recurrences. 597 // If there are, change them into integer recurrences, permitting analysis by 598 // the SCEV routines. 599 // 600 BasicBlock *Header = L->getHeader(); 601 BasicBlock *Preheader = L->getLoopPreheader(); 602 603 std::set<Instruction*> DeadInsts; 604 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { 605 PHINode *PN = cast<PHINode>(I); 606 if (isa<PointerType>(PN->getType())) 607 EliminatePointerRecurrence(PN, Preheader, DeadInsts); 608 } 609 610 if (!DeadInsts.empty()) 611 DeleteTriviallyDeadInstructions(DeadInsts); 612 613 614 // Next, transform all loops nesting inside of this loop. 615 for (LoopInfo::iterator I = L->begin(), E = L->end(); I != E; ++I) 616 runOnLoop(*I); 617 618 // Check to see if this loop has a computable loop-invariant execution count. 619 // If so, this means that we can compute the final value of any expressions 620 // that are recurrent in the loop, and substitute the exit values from the 621 // loop into any instructions outside of the loop that use the final values of 622 // the current expressions. 623 // 624 SCEVHandle IterationCount = SE->getIterationCount(L); 625 if (!isa<SCEVCouldNotCompute>(IterationCount)) 626 RewriteLoopExitValues(L); 627 628 // Next, analyze all of the induction variables in the loop, canonicalizing 629 // auxillary induction variables. 630 std::vector<std::pair<PHINode*, SCEVHandle> > IndVars; 631 632 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) { 633 PHINode *PN = cast<PHINode>(I); 634 if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable! 635 SCEVHandle SCEV = SE->getSCEV(PN); 636 if (SCEV->hasComputableLoopEvolution(L)) 637 // FIXME: Without a strength reduction pass, it is an extremely bad idea 638 // to indvar substitute anything more complex than a linear induction 639 // variable. Doing so will put expensive multiply instructions inside 640 // of the loop. For now just disable indvar subst on anything more 641 // complex than a linear addrec. 642 if (SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(SCEV)) 643 if (AR->getNumOperands() == 2 && isa<SCEVConstant>(AR->getOperand(1))) 644 IndVars.push_back(std::make_pair(PN, SCEV)); 645 } 646 } 647 648 // If there are no induction variables in the loop, there is nothing more to 649 // do. 650 if (IndVars.empty()) { 651 // Actually, if we know how many times the loop iterates, lets insert a 652 // canonical induction variable to help subsequent passes. 653 if (!isa<SCEVCouldNotCompute>(IterationCount)) { 654 SCEVExpander Rewriter(*SE, *LI); 655 Rewriter.getOrInsertCanonicalInductionVariable(L, 656 IterationCount->getType()); 657 LinearFunctionTestReplace(L, IterationCount, Rewriter); 658 } 659 return; 660 } 661 662 // Compute the type of the largest recurrence expression. 663 // 664 const Type *LargestType = IndVars[0].first->getType(); 665 bool DifferingSizes = false; 666 for (unsigned i = 1, e = IndVars.size(); i != e; ++i) { 667 const Type *Ty = IndVars[i].first->getType(); 668 DifferingSizes |= Ty->getPrimitiveSize() != LargestType->getPrimitiveSize(); 669 if (Ty->getPrimitiveSize() > LargestType->getPrimitiveSize()) 670 LargestType = Ty; 671 } 672 673 // Create a rewriter object which we'll use to transform the code with. 674 SCEVExpander Rewriter(*SE, *LI); 675 676 // Now that we know the largest of of the induction variables in this loop, 677 // insert a canonical induction variable of the largest size. 678 LargestType = LargestType->getUnsignedVersion(); 679 Value *IndVar = Rewriter.getOrInsertCanonicalInductionVariable(L,LargestType); 680 ++NumInserted; 681 Changed = true; 682 683 if (!isa<SCEVCouldNotCompute>(IterationCount)) 684 LinearFunctionTestReplace(L, IterationCount, Rewriter); 685 686 // Now that we have a canonical induction variable, we can rewrite any 687 // recurrences in terms of the induction variable. Start with the auxillary 688 // induction variables, and recursively rewrite any of their uses. 689 BasicBlock::iterator InsertPt = Header->begin(); 690 while (isa<PHINode>(InsertPt)) ++InsertPt; 691 692 // If there were induction variables of other sizes, cast the primary 693 // induction variable to the right size for them, avoiding the need for the 694 // code evaluation methods to insert induction variables of different sizes. 695 if (DifferingSizes) { 696 bool InsertedSizes[17] = { false }; 697 InsertedSizes[LargestType->getPrimitiveSize()] = true; 698 for (unsigned i = 0, e = IndVars.size(); i != e; ++i) 699 if (!InsertedSizes[IndVars[i].first->getType()->getPrimitiveSize()]) { 700 PHINode *PN = IndVars[i].first; 701 InsertedSizes[PN->getType()->getPrimitiveSize()] = true; 702 Instruction *New = new CastInst(IndVar, 703 PN->getType()->getUnsignedVersion(), 704 "indvar", InsertPt); 705 Rewriter.addInsertedValue(New, SE->getSCEV(New)); 706 } 707 } 708 709 // If there were induction variables of other sizes, cast the primary 710 // induction variable to the right size for them, avoiding the need for the 711 // code evaluation methods to insert induction variables of different sizes. 712 std::map<unsigned, Value*> InsertedSizes; 713 while (!IndVars.empty()) { 714 PHINode *PN = IndVars.back().first; 715 Value *NewVal = Rewriter.expandCodeFor(IndVars.back().second, InsertPt, 716 PN->getType()); 717 std::string Name = PN->getName(); 718 PN->setName(""); 719 NewVal->setName(Name); 720 721 // Replace the old PHI Node with the inserted computation. 722 PN->replaceAllUsesWith(NewVal); 723 DeadInsts.insert(PN); 724 IndVars.pop_back(); 725 ++NumRemoved; 726 Changed = true; 727 } 728 729#if 0 730 // Now replace all derived expressions in the loop body with simpler 731 // expressions. 732 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i) 733 if (LI->getLoopFor(L->getBlocks()[i]) == L) { // Not in a subloop... 734 BasicBlock *BB = L->getBlocks()[i]; 735 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) 736 if (I->getType()->isInteger() && // Is an integer instruction 737 !I->use_empty() && 738 !Rewriter.isInsertedInstruction(I)) { 739 SCEVHandle SH = SE->getSCEV(I); 740 Value *V = Rewriter.expandCodeFor(SH, I, I->getType()); 741 if (V != I) { 742 if (isa<Instruction>(V)) { 743 std::string Name = I->getName(); 744 I->setName(""); 745 V->setName(Name); 746 } 747 I->replaceAllUsesWith(V); 748 DeadInsts.insert(I); 749 ++NumRemoved; 750 Changed = true; 751 } 752 } 753 } 754#endif 755 756 DeleteTriviallyDeadInstructions(DeadInsts); 757} 758