ArgumentPromotion.cpp revision 3ac79e213ac085a189fae7c7f3591577321307bd
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/Support/CallSite.h" 43#include "llvm/Support/CFG.h" 44#include "llvm/Support/Debug.h" 45#include "llvm/Support/raw_ostream.h" 46#include "llvm/ADT/DepthFirstIterator.h" 47#include "llvm/ADT/Statistic.h" 48#include "llvm/ADT/StringExtras.h" 49#include <set> 50using namespace llvm; 51 52STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted"); 53STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted"); 54STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted"); 55STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated"); 56 57namespace { 58 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass. 59 /// 60 struct ArgPromotion : public CallGraphSCCPass { 61 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 62 AU.addRequired<AliasAnalysis>(); 63 CallGraphSCCPass::getAnalysisUsage(AU); 64 } 65 66 virtual bool runOnSCC(CallGraphSCC &SCC); 67 static char ID; // Pass identification, replacement for typeid 68 explicit ArgPromotion(unsigned maxElements = 3) 69 : CallGraphSCCPass(ID), maxElements(maxElements) { 70 initializeArgPromotionPass(*PassRegistry::getPassRegistry()); 71 } 72 73 /// A vector used to hold the indices of a single GEP instruction 74 typedef std::vector<uint64_t> IndicesVector; 75 76 private: 77 CallGraphNode *PromoteArguments(CallGraphNode *CGN); 78 bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const; 79 CallGraphNode *DoPromotion(Function *F, 80 SmallPtrSet<Argument*, 8> &ArgsToPromote, 81 SmallPtrSet<Argument*, 8> &ByValArgsToTransform); 82 /// The maximum number of elements to expand, or 0 for unlimited. 83 unsigned maxElements; 84 }; 85} 86 87char ArgPromotion::ID = 0; 88INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion", 89 "Promote 'by reference' arguments to scalars", false, false) 90INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 91INITIALIZE_AG_DEPENDENCY(CallGraph) 92INITIALIZE_PASS_END(ArgPromotion, "argpromotion", 93 "Promote 'by reference' arguments to scalars", false, false) 94 95Pass *llvm::createArgumentPromotionPass(unsigned maxElements) { 96 return new ArgPromotion(maxElements); 97} 98 99bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) { 100 bool Changed = false, LocalChange; 101 102 do { // Iterate until we stop promoting from this SCC. 103 LocalChange = false; 104 // Attempt to promote arguments from all functions in this SCC. 105 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 106 if (CallGraphNode *CGN = PromoteArguments(*I)) { 107 LocalChange = true; 108 SCC.ReplaceNode(*I, CGN); 109 } 110 } 111 Changed |= LocalChange; // Remember that we changed something. 112 } while (LocalChange); 113 114 return Changed; 115} 116 117/// PromoteArguments - This method checks the specified function to see if there 118/// are any promotable arguments and if it is safe to promote the function (for 119/// example, all callers are direct). If safe to promote some arguments, it 120/// calls the DoPromotion method. 121/// 122CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) { 123 Function *F = CGN->getFunction(); 124 125 // Make sure that it is local to this module. 126 if (!F || !F->hasLocalLinkage()) return 0; 127 128 // First check: see if there are any pointer arguments! If not, quick exit. 129 SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs; 130 unsigned ArgNo = 0; 131 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 132 I != E; ++I, ++ArgNo) 133 if (I->getType()->isPointerTy()) 134 PointerArgs.push_back(std::pair<Argument*, unsigned>(I, ArgNo)); 135 if (PointerArgs.empty()) return 0; 136 137 // Second check: make sure that all callers are direct callers. We can't 138 // transform functions that have indirect callers. 139 if (F->hasAddressTaken()) 140 return 0; 141 142 // Check to see which arguments are promotable. If an argument is promotable, 143 // add it to ArgsToPromote. 144 SmallPtrSet<Argument*, 8> ArgsToPromote; 145 SmallPtrSet<Argument*, 8> ByValArgsToTransform; 146 for (unsigned i = 0; i != PointerArgs.size(); ++i) { 147 bool isByVal = F->paramHasAttr(PointerArgs[i].second+1, Attribute::ByVal); 148 149 // If this is a byval argument, and if the aggregate type is small, just 150 // pass the elements, which is always safe. 151 Argument *PtrArg = PointerArgs[i].first; 152 if (isByVal) { 153 const Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType(); 154 if (const StructType *STy = dyn_cast<StructType>(AgTy)) { 155 if (maxElements > 0 && STy->getNumElements() > maxElements) { 156 DEBUG(dbgs() << "argpromotion disable promoting argument '" 157 << PtrArg->getName() << "' because it would require adding more" 158 << " than " << maxElements << " arguments to the function.\n"); 159 } else { 160 // If all the elements are single-value types, we can promote it. 161 bool AllSimple = true; 162 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 163 if (!STy->getElementType(i)->isSingleValueType()) { 164 AllSimple = false; 165 break; 166 } 167 168 // Safe to transform, don't even bother trying to "promote" it. 169 // Passing the elements as a scalar will allow scalarrepl to hack on 170 // the new alloca we introduce. 171 if (AllSimple) { 172 ByValArgsToTransform.insert(PtrArg); 173 continue; 174 } 175 } 176 } 177 } 178 179 // Otherwise, see if we can promote the pointer to its value. 180 if (isSafeToPromoteArgument(PtrArg, isByVal)) 181 ArgsToPromote.insert(PtrArg); 182 } 183 184 // No promotable pointer arguments. 185 if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) 186 return 0; 187 188 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform); 189} 190 191/// IsAlwaysValidPointer - Return true if the specified pointer is always legal 192/// to load. 193static bool IsAlwaysValidPointer(Value *V) { 194 if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true; 195 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) 196 return IsAlwaysValidPointer(GEP->getOperand(0)); 197 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 198 if (CE->getOpcode() == Instruction::GetElementPtr) 199 return IsAlwaysValidPointer(CE->getOperand(0)); 200 201 return false; 202} 203 204/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that 205/// all callees pass in a valid pointer for the specified function argument. 206static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) { 207 Function *Callee = Arg->getParent(); 208 209 unsigned ArgNo = std::distance(Callee->arg_begin(), 210 Function::arg_iterator(Arg)); 211 212 // Look at all call sites of the function. At this pointer we know we only 213 // have direct callees. 214 for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end(); 215 UI != E; ++UI) { 216 CallSite CS(*UI); 217 assert(CS && "Should only have direct calls!"); 218 219 if (!IsAlwaysValidPointer(CS.getArgument(ArgNo))) 220 return false; 221 } 222 return true; 223} 224 225/// Returns true if Prefix is a prefix of longer. That means, Longer has a size 226/// that is greater than or equal to the size of prefix, and each of the 227/// elements in Prefix is the same as the corresponding elements in Longer. 228/// 229/// This means it also returns true when Prefix and Longer are equal! 230static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix, 231 const ArgPromotion::IndicesVector &Longer) { 232 if (Prefix.size() > Longer.size()) 233 return false; 234 for (unsigned i = 0, e = Prefix.size(); i != e; ++i) 235 if (Prefix[i] != Longer[i]) 236 return false; 237 return true; 238} 239 240 241/// Checks if Indices, or a prefix of Indices, is in Set. 242static bool PrefixIn(const ArgPromotion::IndicesVector &Indices, 243 std::set<ArgPromotion::IndicesVector> &Set) { 244 std::set<ArgPromotion::IndicesVector>::iterator Low; 245 Low = Set.upper_bound(Indices); 246 if (Low != Set.begin()) 247 Low--; 248 // Low is now the last element smaller than or equal to Indices. This means 249 // it points to a prefix of Indices (possibly Indices itself), if such 250 // prefix exists. 251 // 252 // This load is safe if any prefix of its operands is safe to load. 253 return Low != Set.end() && IsPrefix(*Low, Indices); 254} 255 256/// Mark the given indices (ToMark) as safe in the given set of indices 257/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there 258/// is already a prefix of Indices in Safe, Indices are implicitely marked safe 259/// already. Furthermore, any indices that Indices is itself a prefix of, are 260/// removed from Safe (since they are implicitely safe because of Indices now). 261static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark, 262 std::set<ArgPromotion::IndicesVector> &Safe) { 263 std::set<ArgPromotion::IndicesVector>::iterator Low; 264 Low = Safe.upper_bound(ToMark); 265 // Guard against the case where Safe is empty 266 if (Low != Safe.begin()) 267 Low--; 268 // Low is now the last element smaller than or equal to Indices. This 269 // means it points to a prefix of Indices (possibly Indices itself), if 270 // such prefix exists. 271 if (Low != Safe.end()) { 272 if (IsPrefix(*Low, ToMark)) 273 // If there is already a prefix of these indices (or exactly these 274 // indices) marked a safe, don't bother adding these indices 275 return; 276 277 // Increment Low, so we can use it as a "insert before" hint 278 ++Low; 279 } 280 // Insert 281 Low = Safe.insert(Low, ToMark); 282 ++Low; 283 // If there we're a prefix of longer index list(s), remove those 284 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end(); 285 while (Low != End && IsPrefix(ToMark, *Low)) { 286 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low; 287 ++Low; 288 Safe.erase(Remove); 289 } 290} 291 292/// isSafeToPromoteArgument - As you might guess from the name of this method, 293/// it checks to see if it is both safe and useful to promote the argument. 294/// This method limits promotion of aggregates to only promote up to three 295/// elements of the aggregate in order to avoid exploding the number of 296/// arguments passed in. 297bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { 298 typedef std::set<IndicesVector> GEPIndicesSet; 299 300 // Quick exit for unused arguments 301 if (Arg->use_empty()) 302 return true; 303 304 // We can only promote this argument if all of the uses are loads, or are GEP 305 // instructions (with constant indices) that are subsequently loaded. 306 // 307 // Promoting the argument causes it to be loaded in the caller 308 // unconditionally. This is only safe if we can prove that either the load 309 // would have happened in the callee anyway (ie, there is a load in the entry 310 // block) or the pointer passed in at every call site is guaranteed to be 311 // valid. 312 // In the former case, invalid loads can happen, but would have happened 313 // anyway, in the latter case, invalid loads won't happen. This prevents us 314 // from introducing an invalid load that wouldn't have happened in the 315 // original code. 316 // 317 // This set will contain all sets of indices that are loaded in the entry 318 // block, and thus are safe to unconditionally load in the caller. 319 GEPIndicesSet SafeToUnconditionallyLoad; 320 321 // This set contains all the sets of indices that we are planning to promote. 322 // This makes it possible to limit the number of arguments added. 323 GEPIndicesSet ToPromote; 324 325 // If the pointer is always valid, any load with first index 0 is valid. 326 if (isByVal || AllCalleesPassInValidPointerForArgument(Arg)) 327 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); 328 329 // First, iterate the entry block and mark loads of (geps of) arguments as 330 // safe. 331 BasicBlock *EntryBlock = Arg->getParent()->begin(); 332 // Declare this here so we can reuse it 333 IndicesVector Indices; 334 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end(); 335 I != E; ++I) 336 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 337 Value *V = LI->getPointerOperand(); 338 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { 339 V = GEP->getPointerOperand(); 340 if (V == Arg) { 341 // This load actually loads (part of) Arg? Check the indices then. 342 Indices.reserve(GEP->getNumIndices()); 343 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 344 II != IE; ++II) 345 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) 346 Indices.push_back(CI->getSExtValue()); 347 else 348 // We found a non-constant GEP index for this argument? Bail out 349 // right away, can't promote this argument at all. 350 return false; 351 352 // Indices checked out, mark them as safe 353 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); 354 Indices.clear(); 355 } 356 } else if (V == Arg) { 357 // Direct loads are equivalent to a GEP with a single 0 index. 358 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); 359 } 360 } 361 362 // Now, iterate all uses of the argument to see if there are any uses that are 363 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. 364 SmallVector<LoadInst*, 16> Loads; 365 IndicesVector Operands; 366 for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); 367 UI != E; ++UI) { 368 User *U = *UI; 369 Operands.clear(); 370 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 371 if (LI->isVolatile()) return false; // Don't hack volatile loads 372 Loads.push_back(LI); 373 // Direct loads are equivalent to a GEP with a zero index and then a load. 374 Operands.push_back(0); 375 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 376 if (GEP->use_empty()) { 377 // Dead GEP's cause trouble later. Just remove them if we run into 378 // them. 379 getAnalysis<AliasAnalysis>().deleteValue(GEP); 380 GEP->eraseFromParent(); 381 // TODO: This runs the above loop over and over again for dead GEPs 382 // Couldn't we just do increment the UI iterator earlier and erase the 383 // use? 384 return isSafeToPromoteArgument(Arg, isByVal); 385 } 386 387 // Ensure that all of the indices are constants. 388 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); 389 i != e; ++i) 390 if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) 391 Operands.push_back(C->getSExtValue()); 392 else 393 return false; // Not a constant operand GEP! 394 395 // Ensure that the only users of the GEP are load instructions. 396 for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); 397 UI != E; ++UI) 398 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 399 if (LI->isVolatile()) return false; // Don't hack volatile loads 400 Loads.push_back(LI); 401 } else { 402 // Other uses than load? 403 return false; 404 } 405 } else { 406 return false; // Not a load or a GEP. 407 } 408 409 // Now, see if it is safe to promote this load / loads of this GEP. Loading 410 // is safe if Operands, or a prefix of Operands, is marked as safe. 411 if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) 412 return false; 413 414 // See if we are already promoting a load with these indices. If not, check 415 // to make sure that we aren't promoting too many elements. If so, nothing 416 // to do. 417 if (ToPromote.find(Operands) == ToPromote.end()) { 418 if (maxElements > 0 && ToPromote.size() == maxElements) { 419 DEBUG(dbgs() << "argpromotion not promoting argument '" 420 << Arg->getName() << "' because it would require adding more " 421 << "than " << maxElements << " arguments to the function.\n"); 422 // We limit aggregate promotion to only promoting up to a fixed number 423 // of elements of the aggregate. 424 return false; 425 } 426 ToPromote.insert(Operands); 427 } 428 } 429 430 if (Loads.empty()) return true; // No users, this is a dead argument. 431 432 // Okay, now we know that the argument is only used by load instructions and 433 // it is safe to unconditionally perform all of them. Use alias analysis to 434 // check to see if the pointer is guaranteed to not be modified from entry of 435 // the function to each of the load instructions. 436 437 // Because there could be several/many load instructions, remember which 438 // blocks we know to be transparent to the load. 439 SmallPtrSet<BasicBlock*, 16> TranspBlocks; 440 441 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 442 443 for (unsigned i = 0, e = Loads.size(); i != e; ++i) { 444 // Check to see if the load is invalidated from the start of the block to 445 // the load itself. 446 LoadInst *Load = Loads[i]; 447 BasicBlock *BB = Load->getParent(); 448 449 AliasAnalysis::Location Loc(Load->getPointerOperand(), 450 AA.getTypeStoreSize(Load->getType()), 451 Load->getMetadata(LLVMContext::MD_tbaa)); 452 453 if (AA.canInstructionRangeModify(BB->front(), *Load, Loc)) 454 return false; // Pointer is invalidated! 455 456 // Now check every path from the entry block to the load for transparency. 457 // To do this, we perform a depth first search on the inverse CFG from the 458 // loading block. 459 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 460 BasicBlock *P = *PI; 461 for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> > 462 I = idf_ext_begin(P, TranspBlocks), 463 E = idf_ext_end(P, TranspBlocks); I != E; ++I) 464 if (AA.canBasicBlockModify(**I, Loc)) 465 return false; 466 } 467 } 468 469 // If the path from the entry of the function to each load is free of 470 // instructions that potentially invalidate the load, we can make the 471 // transformation! 472 return true; 473} 474 475/// DoPromotion - This method actually performs the promotion of the specified 476/// arguments, and returns the new function. At this point, we know that it's 477/// safe to do so. 478CallGraphNode *ArgPromotion::DoPromotion(Function *F, 479 SmallPtrSet<Argument*, 8> &ArgsToPromote, 480 SmallPtrSet<Argument*, 8> &ByValArgsToTransform) { 481 482 // Start by computing a new prototype for the function, which is the same as 483 // the old function, but has modified arguments. 484 const FunctionType *FTy = F->getFunctionType(); 485 std::vector<const Type*> Params; 486 487 typedef std::set<IndicesVector> ScalarizeTable; 488 489 // ScalarizedElements - If we are promoting a pointer that has elements 490 // accessed out of it, keep track of which elements are accessed so that we 491 // can add one argument for each. 492 // 493 // Arguments that are directly loaded will have a zero element value here, to 494 // handle cases where there are both a direct load and GEP accesses. 495 // 496 std::map<Argument*, ScalarizeTable> ScalarizedElements; 497 498 // OriginalLoads - Keep track of a representative load instruction from the 499 // original function so that we can tell the alias analysis implementation 500 // what the new GEP/Load instructions we are inserting look like. 501 std::map<IndicesVector, LoadInst*> OriginalLoads; 502 503 // Attributes - Keep track of the parameter attributes for the arguments 504 // that we are *not* promoting. For the ones that we do promote, the parameter 505 // attributes are lost 506 SmallVector<AttributeWithIndex, 8> AttributesVec; 507 const AttrListPtr &PAL = F->getAttributes(); 508 509 // Add any return attributes. 510 if (Attributes attrs = PAL.getRetAttributes()) 511 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 512 513 // First, determine the new argument list 514 unsigned ArgIndex = 1; 515 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; 516 ++I, ++ArgIndex) { 517 if (ByValArgsToTransform.count(I)) { 518 // Simple byval argument? Just add all the struct element types. 519 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 520 const StructType *STy = cast<StructType>(AgTy); 521 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 522 Params.push_back(STy->getElementType(i)); 523 ++NumByValArgsPromoted; 524 } else if (!ArgsToPromote.count(I)) { 525 // Unchanged argument 526 Params.push_back(I->getType()); 527 if (Attributes attrs = PAL.getParamAttributes(ArgIndex)) 528 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), attrs)); 529 } else if (I->use_empty()) { 530 // Dead argument (which are always marked as promotable) 531 ++NumArgumentsDead; 532 } else { 533 // Okay, this is being promoted. This means that the only uses are loads 534 // or GEPs which are only used by loads 535 536 // In this table, we will track which indices are loaded from the argument 537 // (where direct loads are tracked as no indices). 538 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 539 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; 540 ++UI) { 541 Instruction *User = cast<Instruction>(*UI); 542 assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User)); 543 IndicesVector Indices; 544 Indices.reserve(User->getNumOperands() - 1); 545 // Since loads will only have a single operand, and GEPs only a single 546 // non-index operand, this will record direct loads without any indices, 547 // and gep+loads with the GEP indices. 548 for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end(); 549 II != IE; ++II) 550 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue()); 551 // GEPs with a single 0 index can be merged with direct loads 552 if (Indices.size() == 1 && Indices.front() == 0) 553 Indices.clear(); 554 ArgIndices.insert(Indices); 555 LoadInst *OrigLoad; 556 if (LoadInst *L = dyn_cast<LoadInst>(User)) 557 OrigLoad = L; 558 else 559 // Take any load, we will use it only to update Alias Analysis 560 OrigLoad = cast<LoadInst>(User->use_back()); 561 OriginalLoads[Indices] = OrigLoad; 562 } 563 564 // Add a parameter to the function for each element passed in. 565 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 566 E = ArgIndices.end(); SI != E; ++SI) { 567 // not allowed to dereference ->begin() if size() is 0 568 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), 569 SI->begin(), 570 SI->end())); 571 assert(Params.back()); 572 } 573 574 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty()) 575 ++NumArgumentsPromoted; 576 else 577 ++NumAggregatesPromoted; 578 } 579 } 580 581 // Add any function attributes. 582 if (Attributes attrs = PAL.getFnAttributes()) 583 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 584 585 const Type *RetTy = FTy->getReturnType(); 586 587 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 588 // have zero fixed arguments. 589 bool ExtraArgHack = false; 590 if (Params.empty() && FTy->isVarArg()) { 591 ExtraArgHack = true; 592 Params.push_back(Type::getInt32Ty(F->getContext())); 593 } 594 595 // Construct the new function type using the new arguments. 596 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); 597 598 // Create the new function body and insert it into the module. 599 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); 600 NF->copyAttributesFrom(F); 601 602 603 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n" 604 << "From: " << *F); 605 606 // Recompute the parameter attributes list based on the new arguments for 607 // the function. 608 NF->setAttributes(AttrListPtr::get(AttributesVec.begin(), 609 AttributesVec.end())); 610 AttributesVec.clear(); 611 612 F->getParent()->getFunctionList().insert(F, NF); 613 NF->takeName(F); 614 615 // Get the alias analysis information that we need to update to reflect our 616 // changes. 617 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 618 619 // Get the callgraph information that we need to update to reflect our 620 // changes. 621 CallGraph &CG = getAnalysis<CallGraph>(); 622 623 // Get a new callgraph node for NF. 624 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF); 625 626 // Loop over all of the callers of the function, transforming the call sites 627 // to pass in the loaded pointers. 628 // 629 SmallVector<Value*, 16> Args; 630 while (!F->use_empty()) { 631 CallSite CS(F->use_back()); 632 assert(CS.getCalledFunction() == F); 633 Instruction *Call = CS.getInstruction(); 634 const AttrListPtr &CallPAL = CS.getAttributes(); 635 636 // Add any return attributes. 637 if (Attributes attrs = CallPAL.getRetAttributes()) 638 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 639 640 // Loop over the operands, inserting GEP and loads in the caller as 641 // appropriate. 642 CallSite::arg_iterator AI = CS.arg_begin(); 643 ArgIndex = 1; 644 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 645 I != E; ++I, ++AI, ++ArgIndex) 646 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 647 Args.push_back(*AI); // Unmodified argument 648 649 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 650 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 651 652 } else if (ByValArgsToTransform.count(I)) { 653 // Emit a GEP and load for each element of the struct. 654 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 655 const StructType *STy = cast<StructType>(AgTy); 656 Value *Idxs[2] = { 657 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 658 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 659 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 660 Value *Idx = GetElementPtrInst::Create(*AI, Idxs, Idxs+2, 661 (*AI)->getName()+"."+utostr(i), 662 Call); 663 // TODO: Tell AA about the new values? 664 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); 665 } 666 } else if (!I->use_empty()) { 667 // Non-dead argument: insert GEPs and loads as appropriate. 668 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 669 // Store the Value* version of the indices in here, but declare it now 670 // for reuse. 671 std::vector<Value*> Ops; 672 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 673 E = ArgIndices.end(); SI != E; ++SI) { 674 Value *V = *AI; 675 LoadInst *OrigLoad = OriginalLoads[*SI]; 676 if (!SI->empty()) { 677 Ops.reserve(SI->size()); 678 const Type *ElTy = V->getType(); 679 for (IndicesVector::const_iterator II = SI->begin(), 680 IE = SI->end(); II != IE; ++II) { 681 // Use i32 to index structs, and i64 for others (pointers/arrays). 682 // This satisfies GEP constraints. 683 const Type *IdxTy = (ElTy->isStructTy() ? 684 Type::getInt32Ty(F->getContext()) : 685 Type::getInt64Ty(F->getContext())); 686 Ops.push_back(ConstantInt::get(IdxTy, *II)); 687 // Keep track of the type we're currently indexing. 688 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II); 689 } 690 // And create a GEP to extract those indices. 691 V = GetElementPtrInst::Create(V, Ops.begin(), Ops.end(), 692 V->getName()+".idx", Call); 693 Ops.clear(); 694 AA.copyValue(OrigLoad->getOperand(0), V); 695 } 696 // Since we're replacing a load make sure we take the alignment 697 // of the previous load. 698 LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call); 699 newLoad->setAlignment(OrigLoad->getAlignment()); 700 // Transfer the TBAA info too. 701 newLoad->setMetadata(LLVMContext::MD_tbaa, 702 OrigLoad->getMetadata(LLVMContext::MD_tbaa)); 703 Args.push_back(newLoad); 704 AA.copyValue(OrigLoad, Args.back()); 705 } 706 } 707 708 if (ExtraArgHack) 709 Args.push_back(Constant::getNullValue(Type::getInt32Ty(F->getContext()))); 710 711 // Push any varargs arguments on the list. 712 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { 713 Args.push_back(*AI); 714 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 715 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 716 } 717 718 // Add any function attributes. 719 if (Attributes attrs = CallPAL.getFnAttributes()) 720 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 721 722 Instruction *New; 723 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 724 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 725 Args.begin(), Args.end(), "", Call); 726 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 727 cast<InvokeInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 728 AttributesVec.end())); 729 } else { 730 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 731 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 732 cast<CallInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 733 AttributesVec.end())); 734 if (cast<CallInst>(Call)->isTailCall()) 735 cast<CallInst>(New)->setTailCall(); 736 } 737 Args.clear(); 738 AttributesVec.clear(); 739 740 // Update the alias analysis implementation to know that we are replacing 741 // the old call with a new one. 742 AA.replaceWithNewValue(Call, New); 743 744 // Update the callgraph to know that the callsite has been transformed. 745 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()]; 746 CalleeNode->replaceCallEdge(Call, New, NF_CGN); 747 748 if (!Call->use_empty()) { 749 Call->replaceAllUsesWith(New); 750 New->takeName(Call); 751 } 752 753 // Finally, remove the old call from the program, reducing the use-count of 754 // F. 755 Call->eraseFromParent(); 756 } 757 758 // Since we have now created the new function, splice the body of the old 759 // function right into the new function, leaving the old rotting hulk of the 760 // function empty. 761 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 762 763 // Loop over the argument list, transfering uses of the old arguments over to 764 // the new arguments, also transfering over the names as well. 765 // 766 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 767 I2 = NF->arg_begin(); I != E; ++I) { 768 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 769 // If this is an unmodified argument, move the name and users over to the 770 // new version. 771 I->replaceAllUsesWith(I2); 772 I2->takeName(I); 773 AA.replaceWithNewValue(I, I2); 774 ++I2; 775 continue; 776 } 777 778 if (ByValArgsToTransform.count(I)) { 779 // In the callee, we create an alloca, and store each of the new incoming 780 // arguments into the alloca. 781 Instruction *InsertPt = NF->begin()->begin(); 782 783 // Just add all the struct element types. 784 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 785 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 786 const StructType *STy = cast<StructType>(AgTy); 787 Value *Idxs[2] = { 788 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 789 790 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 791 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 792 Value *Idx = 793 GetElementPtrInst::Create(TheAlloca, Idxs, Idxs+2, 794 TheAlloca->getName()+"."+Twine(i), 795 InsertPt); 796 I2->setName(I->getName()+"."+Twine(i)); 797 new StoreInst(I2++, Idx, InsertPt); 798 } 799 800 // Anything that used the arg should now use the alloca. 801 I->replaceAllUsesWith(TheAlloca); 802 TheAlloca->takeName(I); 803 AA.replaceWithNewValue(I, TheAlloca); 804 continue; 805 } 806 807 if (I->use_empty()) { 808 AA.deleteValue(I); 809 continue; 810 } 811 812 // Otherwise, if we promoted this argument, then all users are load 813 // instructions (or GEPs with only load users), and all loads should be 814 // using the new argument that we added. 815 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 816 817 while (!I->use_empty()) { 818 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 819 assert(ArgIndices.begin()->empty() && 820 "Load element should sort to front!"); 821 I2->setName(I->getName()+".val"); 822 LI->replaceAllUsesWith(I2); 823 AA.replaceWithNewValue(LI, I2); 824 LI->eraseFromParent(); 825 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName() 826 << "' in function '" << F->getName() << "'\n"); 827 } else { 828 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 829 IndicesVector Operands; 830 Operands.reserve(GEP->getNumIndices()); 831 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 832 II != IE; ++II) 833 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); 834 835 // GEPs with a single 0 index can be merged with direct loads 836 if (Operands.size() == 1 && Operands.front() == 0) 837 Operands.clear(); 838 839 Function::arg_iterator TheArg = I2; 840 for (ScalarizeTable::iterator It = ArgIndices.begin(); 841 *It != Operands; ++It, ++TheArg) { 842 assert(It != ArgIndices.end() && "GEP not handled??"); 843 } 844 845 std::string NewName = I->getName(); 846 for (unsigned i = 0, e = Operands.size(); i != e; ++i) { 847 NewName += "." + utostr(Operands[i]); 848 } 849 NewName += ".val"; 850 TheArg->setName(NewName); 851 852 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName() 853 << "' of function '" << NF->getName() << "'\n"); 854 855 // All of the uses must be load instructions. Replace them all with 856 // the argument specified by ArgNo. 857 while (!GEP->use_empty()) { 858 LoadInst *L = cast<LoadInst>(GEP->use_back()); 859 L->replaceAllUsesWith(TheArg); 860 AA.replaceWithNewValue(L, TheArg); 861 L->eraseFromParent(); 862 } 863 AA.deleteValue(GEP); 864 GEP->eraseFromParent(); 865 } 866 } 867 868 // Increment I2 past all of the arguments added for this promoted pointer. 869 for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i) 870 ++I2; 871 } 872 873 // Notify the alias analysis implementation that we inserted a new argument. 874 if (ExtraArgHack) 875 AA.copyValue(Constant::getNullValue(Type::getInt32Ty(F->getContext())), 876 NF->arg_begin()); 877 878 879 // Tell the alias analysis that the old function is about to disappear. 880 AA.replaceWithNewValue(F, NF); 881 882 883 NF_CGN->stealCalledFunctionsFrom(CG[F]); 884 885 // Now that the old function is dead, delete it. If there is a dangling 886 // reference to the CallgraphNode, just leave the dead function around for 887 // someone else to nuke. 888 CallGraphNode *CGN = CG[F]; 889 if (CGN->getNumReferences() == 0) 890 delete CG.removeFunctionFromModule(CGN); 891 else 892 F->setLinkage(Function::ExternalLinkage); 893 894 return NF_CGN; 895} 896