ArgumentPromotion.cpp revision ae0a7bc68303ce0c8721f0e981ae602601390e68
1//===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass promotes "by reference" arguments to be "by value" arguments. In 11// practice, this means looking for internal functions that have pointer 12// arguments. If it can prove, through the use of alias analysis, that an 13// argument is *only* loaded, then it can pass the value into the function 14// instead of the address of the value. This can cause recursive simplification 15// of code and lead to the elimination of allocas (especially in C++ template 16// code like the STL). 17// 18// This pass also handles aggregate arguments that are passed into a function, 19// scalarizing them if the elements of the aggregate are only loaded. Note that 20// by default it refuses to scalarize aggregates which would require passing in 21// more than three operands to the function, because passing thousands of 22// operands for a large array or structure is unprofitable! This limit can be 23// configured or disabled, however. 24// 25// Note that this transformation could also be done for arguments that are only 26// stored to (returning the value instead), but does not currently. This case 27// would be best handled when and if LLVM begins supporting multiple return 28// values from functions. 29// 30//===----------------------------------------------------------------------===// 31 32#define DEBUG_TYPE "argpromotion" 33#include "llvm/Transforms/IPO.h" 34#include "llvm/Constants.h" 35#include "llvm/DerivedTypes.h" 36#include "llvm/Module.h" 37#include "llvm/CallGraphSCCPass.h" 38#include "llvm/Instructions.h" 39#include "llvm/LLVMContext.h" 40#include "llvm/Analysis/AliasAnalysis.h" 41#include "llvm/Analysis/CallGraph.h" 42#include "llvm/Target/TargetData.h" 43#include "llvm/Support/CallSite.h" 44#include "llvm/Support/CFG.h" 45#include "llvm/Support/Debug.h" 46#include "llvm/Support/raw_ostream.h" 47#include "llvm/ADT/DepthFirstIterator.h" 48#include "llvm/ADT/Statistic.h" 49#include "llvm/ADT/StringExtras.h" 50#include <set> 51using namespace llvm; 52 53STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted"); 54STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted"); 55STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted"); 56STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated"); 57 58namespace { 59 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass. 60 /// 61 struct ArgPromotion : public CallGraphSCCPass { 62 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 63 AU.addRequired<AliasAnalysis>(); 64 CallGraphSCCPass::getAnalysisUsage(AU); 65 } 66 67 virtual bool runOnSCC(CallGraphSCC &SCC); 68 static char ID; // Pass identification, replacement for typeid 69 explicit ArgPromotion(unsigned maxElements = 3) 70 : CallGraphSCCPass(ID), maxElements(maxElements) {} 71 72 /// A vector used to hold the indices of a single GEP instruction 73 typedef std::vector<uint64_t> IndicesVector; 74 75 private: 76 CallGraphNode *PromoteArguments(CallGraphNode *CGN); 77 bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const; 78 CallGraphNode *DoPromotion(Function *F, 79 SmallPtrSet<Argument*, 8> &ArgsToPromote, 80 SmallPtrSet<Argument*, 8> &ByValArgsToTransform); 81 /// The maximum number of elements to expand, or 0 for unlimited. 82 unsigned maxElements; 83 }; 84} 85 86char ArgPromotion::ID = 0; 87INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion", 88 "Promote 'by reference' arguments to scalars", false, false) 89INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 90INITIALIZE_AG_DEPENDENCY(CallGraph) 91INITIALIZE_PASS_END(ArgPromotion, "argpromotion", 92 "Promote 'by reference' arguments to scalars", false, false) 93 94Pass *llvm::createArgumentPromotionPass(unsigned maxElements) { 95 return new ArgPromotion(maxElements); 96} 97 98bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) { 99 bool Changed = false, LocalChange; 100 101 do { // Iterate until we stop promoting from this SCC. 102 LocalChange = false; 103 // Attempt to promote arguments from all functions in this SCC. 104 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 105 if (CallGraphNode *CGN = PromoteArguments(*I)) { 106 LocalChange = true; 107 SCC.ReplaceNode(*I, CGN); 108 } 109 } 110 Changed |= LocalChange; // Remember that we changed something. 111 } while (LocalChange); 112 113 return Changed; 114} 115 116/// PromoteArguments - This method checks the specified function to see if there 117/// are any promotable arguments and if it is safe to promote the function (for 118/// example, all callers are direct). If safe to promote some arguments, it 119/// calls the DoPromotion method. 120/// 121CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) { 122 Function *F = CGN->getFunction(); 123 124 // Make sure that it is local to this module. 125 if (!F || !F->hasLocalLinkage()) return 0; 126 127 // First check: see if there are any pointer arguments! If not, quick exit. 128 SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs; 129 unsigned ArgNo = 0; 130 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 131 I != E; ++I, ++ArgNo) 132 if (I->getType()->isPointerTy()) 133 PointerArgs.push_back(std::pair<Argument*, unsigned>(I, ArgNo)); 134 if (PointerArgs.empty()) return 0; 135 136 // Second check: make sure that all callers are direct callers. We can't 137 // transform functions that have indirect callers. 138 if (F->hasAddressTaken()) 139 return 0; 140 141 // Check to see which arguments are promotable. If an argument is promotable, 142 // add it to ArgsToPromote. 143 SmallPtrSet<Argument*, 8> ArgsToPromote; 144 SmallPtrSet<Argument*, 8> ByValArgsToTransform; 145 for (unsigned i = 0; i != PointerArgs.size(); ++i) { 146 bool isByVal = F->paramHasAttr(PointerArgs[i].second+1, Attribute::ByVal); 147 148 // If this is a byval argument, and if the aggregate type is small, just 149 // pass the elements, which is always safe. 150 Argument *PtrArg = PointerArgs[i].first; 151 if (isByVal) { 152 const Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType(); 153 if (const StructType *STy = dyn_cast<StructType>(AgTy)) { 154 if (maxElements > 0 && STy->getNumElements() > maxElements) { 155 DEBUG(dbgs() << "argpromotion disable promoting argument '" 156 << PtrArg->getName() << "' because it would require adding more" 157 << " than " << maxElements << " arguments to the function.\n"); 158 } else { 159 // If all the elements are single-value types, we can promote it. 160 bool AllSimple = true; 161 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 162 if (!STy->getElementType(i)->isSingleValueType()) { 163 AllSimple = false; 164 break; 165 } 166 167 // Safe to transform, don't even bother trying to "promote" it. 168 // Passing the elements as a scalar will allow scalarrepl to hack on 169 // the new alloca we introduce. 170 if (AllSimple) { 171 ByValArgsToTransform.insert(PtrArg); 172 continue; 173 } 174 } 175 } 176 } 177 178 // Otherwise, see if we can promote the pointer to its value. 179 if (isSafeToPromoteArgument(PtrArg, isByVal)) 180 ArgsToPromote.insert(PtrArg); 181 } 182 183 // No promotable pointer arguments. 184 if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) 185 return 0; 186 187 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform); 188} 189 190/// IsAlwaysValidPointer - Return true if the specified pointer is always legal 191/// to load. 192static bool IsAlwaysValidPointer(Value *V) { 193 if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true; 194 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) 195 return IsAlwaysValidPointer(GEP->getOperand(0)); 196 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 197 if (CE->getOpcode() == Instruction::GetElementPtr) 198 return IsAlwaysValidPointer(CE->getOperand(0)); 199 200 return false; 201} 202 203/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that 204/// all callees pass in a valid pointer for the specified function argument. 205static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) { 206 Function *Callee = Arg->getParent(); 207 208 unsigned ArgNo = std::distance(Callee->arg_begin(), 209 Function::arg_iterator(Arg)); 210 211 // Look at all call sites of the function. At this pointer we know we only 212 // have direct callees. 213 for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end(); 214 UI != E; ++UI) { 215 CallSite CS(*UI); 216 assert(CS && "Should only have direct calls!"); 217 218 if (!IsAlwaysValidPointer(CS.getArgument(ArgNo))) 219 return false; 220 } 221 return true; 222} 223 224/// Returns true if Prefix is a prefix of longer. That means, Longer has a size 225/// that is greater than or equal to the size of prefix, and each of the 226/// elements in Prefix is the same as the corresponding elements in Longer. 227/// 228/// This means it also returns true when Prefix and Longer are equal! 229static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix, 230 const ArgPromotion::IndicesVector &Longer) { 231 if (Prefix.size() > Longer.size()) 232 return false; 233 for (unsigned i = 0, e = Prefix.size(); i != e; ++i) 234 if (Prefix[i] != Longer[i]) 235 return false; 236 return true; 237} 238 239 240/// Checks if Indices, or a prefix of Indices, is in Set. 241static bool PrefixIn(const ArgPromotion::IndicesVector &Indices, 242 std::set<ArgPromotion::IndicesVector> &Set) { 243 std::set<ArgPromotion::IndicesVector>::iterator Low; 244 Low = Set.upper_bound(Indices); 245 if (Low != Set.begin()) 246 Low--; 247 // Low is now the last element smaller than or equal to Indices. This means 248 // it points to a prefix of Indices (possibly Indices itself), if such 249 // prefix exists. 250 // 251 // This load is safe if any prefix of its operands is safe to load. 252 return Low != Set.end() && IsPrefix(*Low, Indices); 253} 254 255/// Mark the given indices (ToMark) as safe in the given set of indices 256/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there 257/// is already a prefix of Indices in Safe, Indices are implicitely marked safe 258/// already. Furthermore, any indices that Indices is itself a prefix of, are 259/// removed from Safe (since they are implicitely safe because of Indices now). 260static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark, 261 std::set<ArgPromotion::IndicesVector> &Safe) { 262 std::set<ArgPromotion::IndicesVector>::iterator Low; 263 Low = Safe.upper_bound(ToMark); 264 // Guard against the case where Safe is empty 265 if (Low != Safe.begin()) 266 Low--; 267 // Low is now the last element smaller than or equal to Indices. This 268 // means it points to a prefix of Indices (possibly Indices itself), if 269 // such prefix exists. 270 if (Low != Safe.end()) { 271 if (IsPrefix(*Low, ToMark)) 272 // If there is already a prefix of these indices (or exactly these 273 // indices) marked a safe, don't bother adding these indices 274 return; 275 276 // Increment Low, so we can use it as a "insert before" hint 277 ++Low; 278 } 279 // Insert 280 Low = Safe.insert(Low, ToMark); 281 ++Low; 282 // If there we're a prefix of longer index list(s), remove those 283 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end(); 284 while (Low != End && IsPrefix(ToMark, *Low)) { 285 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low; 286 ++Low; 287 Safe.erase(Remove); 288 } 289} 290 291/// isSafeToPromoteArgument - As you might guess from the name of this method, 292/// it checks to see if it is both safe and useful to promote the argument. 293/// This method limits promotion of aggregates to only promote up to three 294/// elements of the aggregate in order to avoid exploding the number of 295/// arguments passed in. 296bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { 297 typedef std::set<IndicesVector> GEPIndicesSet; 298 299 // Quick exit for unused arguments 300 if (Arg->use_empty()) 301 return true; 302 303 // We can only promote this argument if all of the uses are loads, or are GEP 304 // instructions (with constant indices) that are subsequently loaded. 305 // 306 // Promoting the argument causes it to be loaded in the caller 307 // unconditionally. This is only safe if we can prove that either the load 308 // would have happened in the callee anyway (ie, there is a load in the entry 309 // block) or the pointer passed in at every call site is guaranteed to be 310 // valid. 311 // In the former case, invalid loads can happen, but would have happened 312 // anyway, in the latter case, invalid loads won't happen. This prevents us 313 // from introducing an invalid load that wouldn't have happened in the 314 // original code. 315 // 316 // This set will contain all sets of indices that are loaded in the entry 317 // block, and thus are safe to unconditionally load in the caller. 318 GEPIndicesSet SafeToUnconditionallyLoad; 319 320 // This set contains all the sets of indices that we are planning to promote. 321 // This makes it possible to limit the number of arguments added. 322 GEPIndicesSet ToPromote; 323 324 // If the pointer is always valid, any load with first index 0 is valid. 325 if (isByVal || AllCalleesPassInValidPointerForArgument(Arg)) 326 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); 327 328 // First, iterate the entry block and mark loads of (geps of) arguments as 329 // safe. 330 BasicBlock *EntryBlock = Arg->getParent()->begin(); 331 // Declare this here so we can reuse it 332 IndicesVector Indices; 333 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end(); 334 I != E; ++I) 335 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 336 Value *V = LI->getPointerOperand(); 337 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { 338 V = GEP->getPointerOperand(); 339 if (V == Arg) { 340 // This load actually loads (part of) Arg? Check the indices then. 341 Indices.reserve(GEP->getNumIndices()); 342 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 343 II != IE; ++II) 344 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) 345 Indices.push_back(CI->getSExtValue()); 346 else 347 // We found a non-constant GEP index for this argument? Bail out 348 // right away, can't promote this argument at all. 349 return false; 350 351 // Indices checked out, mark them as safe 352 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); 353 Indices.clear(); 354 } 355 } else if (V == Arg) { 356 // Direct loads are equivalent to a GEP with a single 0 index. 357 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); 358 } 359 } 360 361 // Now, iterate all uses of the argument to see if there are any uses that are 362 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. 363 SmallVector<LoadInst*, 16> Loads; 364 IndicesVector Operands; 365 for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); 366 UI != E; ++UI) { 367 User *U = *UI; 368 Operands.clear(); 369 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 370 if (LI->isVolatile()) return false; // Don't hack volatile loads 371 Loads.push_back(LI); 372 // Direct loads are equivalent to a GEP with a zero index and then a load. 373 Operands.push_back(0); 374 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 375 if (GEP->use_empty()) { 376 // Dead GEP's cause trouble later. Just remove them if we run into 377 // them. 378 getAnalysis<AliasAnalysis>().deleteValue(GEP); 379 GEP->eraseFromParent(); 380 // TODO: This runs the above loop over and over again for dead GEPs 381 // Couldn't we just do increment the UI iterator earlier and erase the 382 // use? 383 return isSafeToPromoteArgument(Arg, isByVal); 384 } 385 386 // Ensure that all of the indices are constants. 387 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); 388 i != e; ++i) 389 if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) 390 Operands.push_back(C->getSExtValue()); 391 else 392 return false; // Not a constant operand GEP! 393 394 // Ensure that the only users of the GEP are load instructions. 395 for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); 396 UI != E; ++UI) 397 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 398 if (LI->isVolatile()) return false; // Don't hack volatile loads 399 Loads.push_back(LI); 400 } else { 401 // Other uses than load? 402 return false; 403 } 404 } else { 405 return false; // Not a load or a GEP. 406 } 407 408 // Now, see if it is safe to promote this load / loads of this GEP. Loading 409 // is safe if Operands, or a prefix of Operands, is marked as safe. 410 if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) 411 return false; 412 413 // See if we are already promoting a load with these indices. If not, check 414 // to make sure that we aren't promoting too many elements. If so, nothing 415 // to do. 416 if (ToPromote.find(Operands) == ToPromote.end()) { 417 if (maxElements > 0 && ToPromote.size() == maxElements) { 418 DEBUG(dbgs() << "argpromotion not promoting argument '" 419 << Arg->getName() << "' because it would require adding more " 420 << "than " << maxElements << " arguments to the function.\n"); 421 // We limit aggregate promotion to only promoting up to a fixed number 422 // of elements of the aggregate. 423 return false; 424 } 425 ToPromote.insert(Operands); 426 } 427 } 428 429 if (Loads.empty()) return true; // No users, this is a dead argument. 430 431 // Okay, now we know that the argument is only used by load instructions and 432 // it is safe to unconditionally perform all of them. Use alias analysis to 433 // check to see if the pointer is guaranteed to not be modified from entry of 434 // the function to each of the load instructions. 435 436 // Because there could be several/many load instructions, remember which 437 // blocks we know to be transparent to the load. 438 SmallPtrSet<BasicBlock*, 16> TranspBlocks; 439 440 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 441 TargetData *TD = getAnalysisIfAvailable<TargetData>(); 442 if (!TD) return false; // Without TargetData, assume the worst. 443 444 for (unsigned i = 0, e = Loads.size(); i != e; ++i) { 445 // Check to see if the load is invalidated from the start of the block to 446 // the load itself. 447 LoadInst *Load = Loads[i]; 448 BasicBlock *BB = Load->getParent(); 449 450 const PointerType *LoadTy = 451 cast<PointerType>(Load->getPointerOperand()->getType()); 452 unsigned LoadSize =(unsigned)TD->getTypeStoreSize(LoadTy->getElementType()); 453 454 if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize)) 455 return false; // Pointer is invalidated! 456 457 // Now check every path from the entry block to the load for transparency. 458 // To do this, we perform a depth first search on the inverse CFG from the 459 // loading block. 460 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 461 BasicBlock *P = *PI; 462 for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> > 463 I = idf_ext_begin(P, TranspBlocks), 464 E = idf_ext_end(P, TranspBlocks); I != E; ++I) 465 if (AA.canBasicBlockModify(**I, Arg, LoadSize)) 466 return false; 467 } 468 } 469 470 // If the path from the entry of the function to each load is free of 471 // instructions that potentially invalidate the load, we can make the 472 // transformation! 473 return true; 474} 475 476/// DoPromotion - This method actually performs the promotion of the specified 477/// arguments, and returns the new function. At this point, we know that it's 478/// safe to do so. 479CallGraphNode *ArgPromotion::DoPromotion(Function *F, 480 SmallPtrSet<Argument*, 8> &ArgsToPromote, 481 SmallPtrSet<Argument*, 8> &ByValArgsToTransform) { 482 483 // Start by computing a new prototype for the function, which is the same as 484 // the old function, but has modified arguments. 485 const FunctionType *FTy = F->getFunctionType(); 486 std::vector<const Type*> Params; 487 488 typedef std::set<IndicesVector> ScalarizeTable; 489 490 // ScalarizedElements - If we are promoting a pointer that has elements 491 // accessed out of it, keep track of which elements are accessed so that we 492 // can add one argument for each. 493 // 494 // Arguments that are directly loaded will have a zero element value here, to 495 // handle cases where there are both a direct load and GEP accesses. 496 // 497 std::map<Argument*, ScalarizeTable> ScalarizedElements; 498 499 // OriginalLoads - Keep track of a representative load instruction from the 500 // original function so that we can tell the alias analysis implementation 501 // what the new GEP/Load instructions we are inserting look like. 502 std::map<IndicesVector, LoadInst*> OriginalLoads; 503 504 // Attributes - Keep track of the parameter attributes for the arguments 505 // that we are *not* promoting. For the ones that we do promote, the parameter 506 // attributes are lost 507 SmallVector<AttributeWithIndex, 8> AttributesVec; 508 const AttrListPtr &PAL = F->getAttributes(); 509 510 // Add any return attributes. 511 if (Attributes attrs = PAL.getRetAttributes()) 512 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 513 514 // First, determine the new argument list 515 unsigned ArgIndex = 1; 516 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; 517 ++I, ++ArgIndex) { 518 if (ByValArgsToTransform.count(I)) { 519 // Simple byval argument? Just add all the struct element types. 520 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 521 const StructType *STy = cast<StructType>(AgTy); 522 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 523 Params.push_back(STy->getElementType(i)); 524 ++NumByValArgsPromoted; 525 } else if (!ArgsToPromote.count(I)) { 526 // Unchanged argument 527 Params.push_back(I->getType()); 528 if (Attributes attrs = PAL.getParamAttributes(ArgIndex)) 529 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), attrs)); 530 } else if (I->use_empty()) { 531 // Dead argument (which are always marked as promotable) 532 ++NumArgumentsDead; 533 } else { 534 // Okay, this is being promoted. This means that the only uses are loads 535 // or GEPs which are only used by loads 536 537 // In this table, we will track which indices are loaded from the argument 538 // (where direct loads are tracked as no indices). 539 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 540 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; 541 ++UI) { 542 Instruction *User = cast<Instruction>(*UI); 543 assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User)); 544 IndicesVector Indices; 545 Indices.reserve(User->getNumOperands() - 1); 546 // Since loads will only have a single operand, and GEPs only a single 547 // non-index operand, this will record direct loads without any indices, 548 // and gep+loads with the GEP indices. 549 for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end(); 550 II != IE; ++II) 551 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue()); 552 // GEPs with a single 0 index can be merged with direct loads 553 if (Indices.size() == 1 && Indices.front() == 0) 554 Indices.clear(); 555 ArgIndices.insert(Indices); 556 LoadInst *OrigLoad; 557 if (LoadInst *L = dyn_cast<LoadInst>(User)) 558 OrigLoad = L; 559 else 560 // Take any load, we will use it only to update Alias Analysis 561 OrigLoad = cast<LoadInst>(User->use_back()); 562 OriginalLoads[Indices] = OrigLoad; 563 } 564 565 // Add a parameter to the function for each element passed in. 566 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 567 E = ArgIndices.end(); SI != E; ++SI) { 568 // not allowed to dereference ->begin() if size() is 0 569 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), 570 SI->begin(), 571 SI->end())); 572 assert(Params.back()); 573 } 574 575 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty()) 576 ++NumArgumentsPromoted; 577 else 578 ++NumAggregatesPromoted; 579 } 580 } 581 582 // Add any function attributes. 583 if (Attributes attrs = PAL.getFnAttributes()) 584 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 585 586 const Type *RetTy = FTy->getReturnType(); 587 588 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 589 // have zero fixed arguments. 590 bool ExtraArgHack = false; 591 if (Params.empty() && FTy->isVarArg()) { 592 ExtraArgHack = true; 593 Params.push_back(Type::getInt32Ty(F->getContext())); 594 } 595 596 // Construct the new function type using the new arguments. 597 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); 598 599 // Create the new function body and insert it into the module. 600 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); 601 NF->copyAttributesFrom(F); 602 603 604 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n" 605 << "From: " << *F); 606 607 // Recompute the parameter attributes list based on the new arguments for 608 // the function. 609 NF->setAttributes(AttrListPtr::get(AttributesVec.begin(), 610 AttributesVec.end())); 611 AttributesVec.clear(); 612 613 F->getParent()->getFunctionList().insert(F, NF); 614 NF->takeName(F); 615 616 // Get the alias analysis information that we need to update to reflect our 617 // changes. 618 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 619 620 // Get the callgraph information that we need to update to reflect our 621 // changes. 622 CallGraph &CG = getAnalysis<CallGraph>(); 623 624 // Get a new callgraph node for NF. 625 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF); 626 627 // Loop over all of the callers of the function, transforming the call sites 628 // to pass in the loaded pointers. 629 // 630 SmallVector<Value*, 16> Args; 631 while (!F->use_empty()) { 632 CallSite CS(F->use_back()); 633 assert(CS.getCalledFunction() == F); 634 Instruction *Call = CS.getInstruction(); 635 const AttrListPtr &CallPAL = CS.getAttributes(); 636 637 // Add any return attributes. 638 if (Attributes attrs = CallPAL.getRetAttributes()) 639 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 640 641 // Loop over the operands, inserting GEP and loads in the caller as 642 // appropriate. 643 CallSite::arg_iterator AI = CS.arg_begin(); 644 ArgIndex = 1; 645 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 646 I != E; ++I, ++AI, ++ArgIndex) 647 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 648 Args.push_back(*AI); // Unmodified argument 649 650 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 651 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 652 653 } else if (ByValArgsToTransform.count(I)) { 654 // Emit a GEP and load for each element of the struct. 655 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 656 const StructType *STy = cast<StructType>(AgTy); 657 Value *Idxs[2] = { 658 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 659 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 660 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 661 Value *Idx = GetElementPtrInst::Create(*AI, Idxs, Idxs+2, 662 (*AI)->getName()+"."+utostr(i), 663 Call); 664 // TODO: Tell AA about the new values? 665 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); 666 } 667 } else if (!I->use_empty()) { 668 // Non-dead argument: insert GEPs and loads as appropriate. 669 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 670 // Store the Value* version of the indices in here, but declare it now 671 // for reuse. 672 std::vector<Value*> Ops; 673 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 674 E = ArgIndices.end(); SI != E; ++SI) { 675 Value *V = *AI; 676 LoadInst *OrigLoad = OriginalLoads[*SI]; 677 if (!SI->empty()) { 678 Ops.reserve(SI->size()); 679 const Type *ElTy = V->getType(); 680 for (IndicesVector::const_iterator II = SI->begin(), 681 IE = SI->end(); II != IE; ++II) { 682 // Use i32 to index structs, and i64 for others (pointers/arrays). 683 // This satisfies GEP constraints. 684 const Type *IdxTy = (ElTy->isStructTy() ? 685 Type::getInt32Ty(F->getContext()) : 686 Type::getInt64Ty(F->getContext())); 687 Ops.push_back(ConstantInt::get(IdxTy, *II)); 688 // Keep track of the type we're currently indexing. 689 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II); 690 } 691 // And create a GEP to extract those indices. 692 V = GetElementPtrInst::Create(V, Ops.begin(), Ops.end(), 693 V->getName()+".idx", Call); 694 Ops.clear(); 695 AA.copyValue(OrigLoad->getOperand(0), V); 696 } 697 // Since we're replacing a load make sure we take the alignment 698 // of the previous load. 699 LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call); 700 newLoad->setAlignment(OrigLoad->getAlignment()); 701 Args.push_back(newLoad); 702 AA.copyValue(OrigLoad, Args.back()); 703 } 704 } 705 706 if (ExtraArgHack) 707 Args.push_back(Constant::getNullValue(Type::getInt32Ty(F->getContext()))); 708 709 // Push any varargs arguments on the list. 710 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { 711 Args.push_back(*AI); 712 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 713 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 714 } 715 716 // Add any function attributes. 717 if (Attributes attrs = CallPAL.getFnAttributes()) 718 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 719 720 Instruction *New; 721 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 722 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 723 Args.begin(), Args.end(), "", Call); 724 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 725 cast<InvokeInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 726 AttributesVec.end())); 727 } else { 728 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 729 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 730 cast<CallInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 731 AttributesVec.end())); 732 if (cast<CallInst>(Call)->isTailCall()) 733 cast<CallInst>(New)->setTailCall(); 734 } 735 Args.clear(); 736 AttributesVec.clear(); 737 738 // Update the alias analysis implementation to know that we are replacing 739 // the old call with a new one. 740 AA.replaceWithNewValue(Call, New); 741 742 // Update the callgraph to know that the callsite has been transformed. 743 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()]; 744 CalleeNode->replaceCallEdge(Call, New, NF_CGN); 745 746 if (!Call->use_empty()) { 747 Call->replaceAllUsesWith(New); 748 New->takeName(Call); 749 } 750 751 // Finally, remove the old call from the program, reducing the use-count of 752 // F. 753 Call->eraseFromParent(); 754 } 755 756 // Since we have now created the new function, splice the body of the old 757 // function right into the new function, leaving the old rotting hulk of the 758 // function empty. 759 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 760 761 // Loop over the argument list, transfering uses of the old arguments over to 762 // the new arguments, also transfering over the names as well. 763 // 764 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 765 I2 = NF->arg_begin(); I != E; ++I) { 766 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 767 // If this is an unmodified argument, move the name and users over to the 768 // new version. 769 I->replaceAllUsesWith(I2); 770 I2->takeName(I); 771 AA.replaceWithNewValue(I, I2); 772 ++I2; 773 continue; 774 } 775 776 if (ByValArgsToTransform.count(I)) { 777 // In the callee, we create an alloca, and store each of the new incoming 778 // arguments into the alloca. 779 Instruction *InsertPt = NF->begin()->begin(); 780 781 // Just add all the struct element types. 782 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 783 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 784 const StructType *STy = cast<StructType>(AgTy); 785 Value *Idxs[2] = { 786 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 787 788 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 789 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 790 Value *Idx = 791 GetElementPtrInst::Create(TheAlloca, Idxs, Idxs+2, 792 TheAlloca->getName()+"."+Twine(i), 793 InsertPt); 794 I2->setName(I->getName()+"."+Twine(i)); 795 new StoreInst(I2++, Idx, InsertPt); 796 } 797 798 // Anything that used the arg should now use the alloca. 799 I->replaceAllUsesWith(TheAlloca); 800 TheAlloca->takeName(I); 801 AA.replaceWithNewValue(I, TheAlloca); 802 continue; 803 } 804 805 if (I->use_empty()) { 806 AA.deleteValue(I); 807 continue; 808 } 809 810 // Otherwise, if we promoted this argument, then all users are load 811 // instructions (or GEPs with only load users), and all loads should be 812 // using the new argument that we added. 813 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 814 815 while (!I->use_empty()) { 816 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 817 assert(ArgIndices.begin()->empty() && 818 "Load element should sort to front!"); 819 I2->setName(I->getName()+".val"); 820 LI->replaceAllUsesWith(I2); 821 AA.replaceWithNewValue(LI, I2); 822 LI->eraseFromParent(); 823 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName() 824 << "' in function '" << F->getName() << "'\n"); 825 } else { 826 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 827 IndicesVector Operands; 828 Operands.reserve(GEP->getNumIndices()); 829 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 830 II != IE; ++II) 831 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); 832 833 // GEPs with a single 0 index can be merged with direct loads 834 if (Operands.size() == 1 && Operands.front() == 0) 835 Operands.clear(); 836 837 Function::arg_iterator TheArg = I2; 838 for (ScalarizeTable::iterator It = ArgIndices.begin(); 839 *It != Operands; ++It, ++TheArg) { 840 assert(It != ArgIndices.end() && "GEP not handled??"); 841 } 842 843 std::string NewName = I->getName(); 844 for (unsigned i = 0, e = Operands.size(); i != e; ++i) { 845 NewName += "." + utostr(Operands[i]); 846 } 847 NewName += ".val"; 848 TheArg->setName(NewName); 849 850 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName() 851 << "' of function '" << NF->getName() << "'\n"); 852 853 // All of the uses must be load instructions. Replace them all with 854 // the argument specified by ArgNo. 855 while (!GEP->use_empty()) { 856 LoadInst *L = cast<LoadInst>(GEP->use_back()); 857 L->replaceAllUsesWith(TheArg); 858 AA.replaceWithNewValue(L, TheArg); 859 L->eraseFromParent(); 860 } 861 AA.deleteValue(GEP); 862 GEP->eraseFromParent(); 863 } 864 } 865 866 // Increment I2 past all of the arguments added for this promoted pointer. 867 for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i) 868 ++I2; 869 } 870 871 // Notify the alias analysis implementation that we inserted a new argument. 872 if (ExtraArgHack) 873 AA.copyValue(Constant::getNullValue(Type::getInt32Ty(F->getContext())), 874 NF->arg_begin()); 875 876 877 // Tell the alias analysis that the old function is about to disappear. 878 AA.replaceWithNewValue(F, NF); 879 880 881 NF_CGN->stealCalledFunctionsFrom(CG[F]); 882 883 // Now that the old function is dead, delete it. If there is a dangling 884 // reference to the CallgraphNode, just leave the dead function around for 885 // someone else to nuke. 886 CallGraphNode *CGN = CG[F]; 887 if (CGN->getNumReferences() == 0) 888 delete CG.removeFunctionFromModule(CGN); 889 else 890 F->setLinkage(Function::ExternalLinkage); 891 892 return NF_CGN; 893} 894