ArgumentPromotion.cpp revision 2ab36d350293c77fc8941ce1023e4899df7e3a82
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_PASS_END(ArgPromotion, "argpromotion", 91 "Promote 'by reference' arguments to scalars", false, false) 92 93Pass *llvm::createArgumentPromotionPass(unsigned maxElements) { 94 return new ArgPromotion(maxElements); 95} 96 97bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) { 98 bool Changed = false, LocalChange; 99 100 do { // Iterate until we stop promoting from this SCC. 101 LocalChange = false; 102 // Attempt to promote arguments from all functions in this SCC. 103 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 104 if (CallGraphNode *CGN = PromoteArguments(*I)) { 105 LocalChange = true; 106 SCC.ReplaceNode(*I, CGN); 107 } 108 } 109 Changed |= LocalChange; // Remember that we changed something. 110 } while (LocalChange); 111 112 return Changed; 113} 114 115/// PromoteArguments - This method checks the specified function to see if there 116/// are any promotable arguments and if it is safe to promote the function (for 117/// example, all callers are direct). If safe to promote some arguments, it 118/// calls the DoPromotion method. 119/// 120CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) { 121 Function *F = CGN->getFunction(); 122 123 // Make sure that it is local to this module. 124 if (!F || !F->hasLocalLinkage()) return 0; 125 126 // First check: see if there are any pointer arguments! If not, quick exit. 127 SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs; 128 unsigned ArgNo = 0; 129 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 130 I != E; ++I, ++ArgNo) 131 if (I->getType()->isPointerTy()) 132 PointerArgs.push_back(std::pair<Argument*, unsigned>(I, ArgNo)); 133 if (PointerArgs.empty()) return 0; 134 135 // Second check: make sure that all callers are direct callers. We can't 136 // transform functions that have indirect callers. 137 if (F->hasAddressTaken()) 138 return 0; 139 140 // Check to see which arguments are promotable. If an argument is promotable, 141 // add it to ArgsToPromote. 142 SmallPtrSet<Argument*, 8> ArgsToPromote; 143 SmallPtrSet<Argument*, 8> ByValArgsToTransform; 144 for (unsigned i = 0; i != PointerArgs.size(); ++i) { 145 bool isByVal = F->paramHasAttr(PointerArgs[i].second+1, Attribute::ByVal); 146 147 // If this is a byval argument, and if the aggregate type is small, just 148 // pass the elements, which is always safe. 149 Argument *PtrArg = PointerArgs[i].first; 150 if (isByVal) { 151 const Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType(); 152 if (const StructType *STy = dyn_cast<StructType>(AgTy)) { 153 if (maxElements > 0 && STy->getNumElements() > maxElements) { 154 DEBUG(dbgs() << "argpromotion disable promoting argument '" 155 << PtrArg->getName() << "' because it would require adding more" 156 << " than " << maxElements << " arguments to the function.\n"); 157 } else { 158 // If all the elements are single-value types, we can promote it. 159 bool AllSimple = true; 160 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 161 if (!STy->getElementType(i)->isSingleValueType()) { 162 AllSimple = false; 163 break; 164 } 165 166 // Safe to transform, don't even bother trying to "promote" it. 167 // Passing the elements as a scalar will allow scalarrepl to hack on 168 // the new alloca we introduce. 169 if (AllSimple) { 170 ByValArgsToTransform.insert(PtrArg); 171 continue; 172 } 173 } 174 } 175 } 176 177 // Otherwise, see if we can promote the pointer to its value. 178 if (isSafeToPromoteArgument(PtrArg, isByVal)) 179 ArgsToPromote.insert(PtrArg); 180 } 181 182 // No promotable pointer arguments. 183 if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) 184 return 0; 185 186 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform); 187} 188 189/// IsAlwaysValidPointer - Return true if the specified pointer is always legal 190/// to load. 191static bool IsAlwaysValidPointer(Value *V) { 192 if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true; 193 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) 194 return IsAlwaysValidPointer(GEP->getOperand(0)); 195 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 196 if (CE->getOpcode() == Instruction::GetElementPtr) 197 return IsAlwaysValidPointer(CE->getOperand(0)); 198 199 return false; 200} 201 202/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that 203/// all callees pass in a valid pointer for the specified function argument. 204static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) { 205 Function *Callee = Arg->getParent(); 206 207 unsigned ArgNo = std::distance(Callee->arg_begin(), 208 Function::arg_iterator(Arg)); 209 210 // Look at all call sites of the function. At this pointer we know we only 211 // have direct callees. 212 for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end(); 213 UI != E; ++UI) { 214 CallSite CS(*UI); 215 assert(CS && "Should only have direct calls!"); 216 217 if (!IsAlwaysValidPointer(CS.getArgument(ArgNo))) 218 return false; 219 } 220 return true; 221} 222 223/// Returns true if Prefix is a prefix of longer. That means, Longer has a size 224/// that is greater than or equal to the size of prefix, and each of the 225/// elements in Prefix is the same as the corresponding elements in Longer. 226/// 227/// This means it also returns true when Prefix and Longer are equal! 228static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix, 229 const ArgPromotion::IndicesVector &Longer) { 230 if (Prefix.size() > Longer.size()) 231 return false; 232 for (unsigned i = 0, e = Prefix.size(); i != e; ++i) 233 if (Prefix[i] != Longer[i]) 234 return false; 235 return true; 236} 237 238 239/// Checks if Indices, or a prefix of Indices, is in Set. 240static bool PrefixIn(const ArgPromotion::IndicesVector &Indices, 241 std::set<ArgPromotion::IndicesVector> &Set) { 242 std::set<ArgPromotion::IndicesVector>::iterator Low; 243 Low = Set.upper_bound(Indices); 244 if (Low != Set.begin()) 245 Low--; 246 // Low is now the last element smaller than or equal to Indices. This means 247 // it points to a prefix of Indices (possibly Indices itself), if such 248 // prefix exists. 249 // 250 // This load is safe if any prefix of its operands is safe to load. 251 return Low != Set.end() && IsPrefix(*Low, Indices); 252} 253 254/// Mark the given indices (ToMark) as safe in the given set of indices 255/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there 256/// is already a prefix of Indices in Safe, Indices are implicitely marked safe 257/// already. Furthermore, any indices that Indices is itself a prefix of, are 258/// removed from Safe (since they are implicitely safe because of Indices now). 259static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark, 260 std::set<ArgPromotion::IndicesVector> &Safe) { 261 std::set<ArgPromotion::IndicesVector>::iterator Low; 262 Low = Safe.upper_bound(ToMark); 263 // Guard against the case where Safe is empty 264 if (Low != Safe.begin()) 265 Low--; 266 // Low is now the last element smaller than or equal to Indices. This 267 // means it points to a prefix of Indices (possibly Indices itself), if 268 // such prefix exists. 269 if (Low != Safe.end()) { 270 if (IsPrefix(*Low, ToMark)) 271 // If there is already a prefix of these indices (or exactly these 272 // indices) marked a safe, don't bother adding these indices 273 return; 274 275 // Increment Low, so we can use it as a "insert before" hint 276 ++Low; 277 } 278 // Insert 279 Low = Safe.insert(Low, ToMark); 280 ++Low; 281 // If there we're a prefix of longer index list(s), remove those 282 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end(); 283 while (Low != End && IsPrefix(ToMark, *Low)) { 284 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low; 285 ++Low; 286 Safe.erase(Remove); 287 } 288} 289 290/// isSafeToPromoteArgument - As you might guess from the name of this method, 291/// it checks to see if it is both safe and useful to promote the argument. 292/// This method limits promotion of aggregates to only promote up to three 293/// elements of the aggregate in order to avoid exploding the number of 294/// arguments passed in. 295bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { 296 typedef std::set<IndicesVector> GEPIndicesSet; 297 298 // Quick exit for unused arguments 299 if (Arg->use_empty()) 300 return true; 301 302 // We can only promote this argument if all of the uses are loads, or are GEP 303 // instructions (with constant indices) that are subsequently loaded. 304 // 305 // Promoting the argument causes it to be loaded in the caller 306 // unconditionally. This is only safe if we can prove that either the load 307 // would have happened in the callee anyway (ie, there is a load in the entry 308 // block) or the pointer passed in at every call site is guaranteed to be 309 // valid. 310 // In the former case, invalid loads can happen, but would have happened 311 // anyway, in the latter case, invalid loads won't happen. This prevents us 312 // from introducing an invalid load that wouldn't have happened in the 313 // original code. 314 // 315 // This set will contain all sets of indices that are loaded in the entry 316 // block, and thus are safe to unconditionally load in the caller. 317 GEPIndicesSet SafeToUnconditionallyLoad; 318 319 // This set contains all the sets of indices that we are planning to promote. 320 // This makes it possible to limit the number of arguments added. 321 GEPIndicesSet ToPromote; 322 323 // If the pointer is always valid, any load with first index 0 is valid. 324 if (isByVal || AllCalleesPassInValidPointerForArgument(Arg)) 325 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); 326 327 // First, iterate the entry block and mark loads of (geps of) arguments as 328 // safe. 329 BasicBlock *EntryBlock = Arg->getParent()->begin(); 330 // Declare this here so we can reuse it 331 IndicesVector Indices; 332 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end(); 333 I != E; ++I) 334 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 335 Value *V = LI->getPointerOperand(); 336 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { 337 V = GEP->getPointerOperand(); 338 if (V == Arg) { 339 // This load actually loads (part of) Arg? Check the indices then. 340 Indices.reserve(GEP->getNumIndices()); 341 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 342 II != IE; ++II) 343 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) 344 Indices.push_back(CI->getSExtValue()); 345 else 346 // We found a non-constant GEP index for this argument? Bail out 347 // right away, can't promote this argument at all. 348 return false; 349 350 // Indices checked out, mark them as safe 351 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); 352 Indices.clear(); 353 } 354 } else if (V == Arg) { 355 // Direct loads are equivalent to a GEP with a single 0 index. 356 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); 357 } 358 } 359 360 // Now, iterate all uses of the argument to see if there are any uses that are 361 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. 362 SmallVector<LoadInst*, 16> Loads; 363 IndicesVector Operands; 364 for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); 365 UI != E; ++UI) { 366 User *U = *UI; 367 Operands.clear(); 368 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 369 if (LI->isVolatile()) return false; // Don't hack volatile loads 370 Loads.push_back(LI); 371 // Direct loads are equivalent to a GEP with a zero index and then a load. 372 Operands.push_back(0); 373 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 374 if (GEP->use_empty()) { 375 // Dead GEP's cause trouble later. Just remove them if we run into 376 // them. 377 getAnalysis<AliasAnalysis>().deleteValue(GEP); 378 GEP->eraseFromParent(); 379 // TODO: This runs the above loop over and over again for dead GEPs 380 // Couldn't we just do increment the UI iterator earlier and erase the 381 // use? 382 return isSafeToPromoteArgument(Arg, isByVal); 383 } 384 385 // Ensure that all of the indices are constants. 386 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); 387 i != e; ++i) 388 if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) 389 Operands.push_back(C->getSExtValue()); 390 else 391 return false; // Not a constant operand GEP! 392 393 // Ensure that the only users of the GEP are load instructions. 394 for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); 395 UI != E; ++UI) 396 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 397 if (LI->isVolatile()) return false; // Don't hack volatile loads 398 Loads.push_back(LI); 399 } else { 400 // Other uses than load? 401 return false; 402 } 403 } else { 404 return false; // Not a load or a GEP. 405 } 406 407 // Now, see if it is safe to promote this load / loads of this GEP. Loading 408 // is safe if Operands, or a prefix of Operands, is marked as safe. 409 if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) 410 return false; 411 412 // See if we are already promoting a load with these indices. If not, check 413 // to make sure that we aren't promoting too many elements. If so, nothing 414 // to do. 415 if (ToPromote.find(Operands) == ToPromote.end()) { 416 if (maxElements > 0 && ToPromote.size() == maxElements) { 417 DEBUG(dbgs() << "argpromotion not promoting argument '" 418 << Arg->getName() << "' because it would require adding more " 419 << "than " << maxElements << " arguments to the function.\n"); 420 // We limit aggregate promotion to only promoting up to a fixed number 421 // of elements of the aggregate. 422 return false; 423 } 424 ToPromote.insert(Operands); 425 } 426 } 427 428 if (Loads.empty()) return true; // No users, this is a dead argument. 429 430 // Okay, now we know that the argument is only used by load instructions and 431 // it is safe to unconditionally perform all of them. Use alias analysis to 432 // check to see if the pointer is guaranteed to not be modified from entry of 433 // the function to each of the load instructions. 434 435 // Because there could be several/many load instructions, remember which 436 // blocks we know to be transparent to the load. 437 SmallPtrSet<BasicBlock*, 16> TranspBlocks; 438 439 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 440 TargetData *TD = getAnalysisIfAvailable<TargetData>(); 441 if (!TD) return false; // Without TargetData, assume the worst. 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 const PointerType *LoadTy = 450 cast<PointerType>(Load->getPointerOperand()->getType()); 451 unsigned LoadSize =(unsigned)TD->getTypeStoreSize(LoadTy->getElementType()); 452 453 if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize)) 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, Arg, LoadSize)) 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 Args.push_back(newLoad); 701 AA.copyValue(OrigLoad, Args.back()); 702 } 703 } 704 705 if (ExtraArgHack) 706 Args.push_back(Constant::getNullValue(Type::getInt32Ty(F->getContext()))); 707 708 // Push any varargs arguments on the list. 709 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { 710 Args.push_back(*AI); 711 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 712 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 713 } 714 715 // Add any function attributes. 716 if (Attributes attrs = CallPAL.getFnAttributes()) 717 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 718 719 Instruction *New; 720 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 721 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 722 Args.begin(), Args.end(), "", Call); 723 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 724 cast<InvokeInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 725 AttributesVec.end())); 726 } else { 727 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 728 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 729 cast<CallInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 730 AttributesVec.end())); 731 if (cast<CallInst>(Call)->isTailCall()) 732 cast<CallInst>(New)->setTailCall(); 733 } 734 Args.clear(); 735 AttributesVec.clear(); 736 737 // Update the alias analysis implementation to know that we are replacing 738 // the old call with a new one. 739 AA.replaceWithNewValue(Call, New); 740 741 // Update the callgraph to know that the callsite has been transformed. 742 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()]; 743 CalleeNode->replaceCallEdge(Call, New, NF_CGN); 744 745 if (!Call->use_empty()) { 746 Call->replaceAllUsesWith(New); 747 New->takeName(Call); 748 } 749 750 // Finally, remove the old call from the program, reducing the use-count of 751 // F. 752 Call->eraseFromParent(); 753 } 754 755 // Since we have now created the new function, splice the body of the old 756 // function right into the new function, leaving the old rotting hulk of the 757 // function empty. 758 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 759 760 // Loop over the argument list, transfering uses of the old arguments over to 761 // the new arguments, also transfering over the names as well. 762 // 763 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 764 I2 = NF->arg_begin(); I != E; ++I) { 765 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 766 // If this is an unmodified argument, move the name and users over to the 767 // new version. 768 I->replaceAllUsesWith(I2); 769 I2->takeName(I); 770 AA.replaceWithNewValue(I, I2); 771 ++I2; 772 continue; 773 } 774 775 if (ByValArgsToTransform.count(I)) { 776 // In the callee, we create an alloca, and store each of the new incoming 777 // arguments into the alloca. 778 Instruction *InsertPt = NF->begin()->begin(); 779 780 // Just add all the struct element types. 781 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 782 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 783 const StructType *STy = cast<StructType>(AgTy); 784 Value *Idxs[2] = { 785 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 786 787 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 788 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 789 Value *Idx = 790 GetElementPtrInst::Create(TheAlloca, Idxs, Idxs+2, 791 TheAlloca->getName()+"."+Twine(i), 792 InsertPt); 793 I2->setName(I->getName()+"."+Twine(i)); 794 new StoreInst(I2++, Idx, InsertPt); 795 } 796 797 // Anything that used the arg should now use the alloca. 798 I->replaceAllUsesWith(TheAlloca); 799 TheAlloca->takeName(I); 800 AA.replaceWithNewValue(I, TheAlloca); 801 continue; 802 } 803 804 if (I->use_empty()) { 805 AA.deleteValue(I); 806 continue; 807 } 808 809 // Otherwise, if we promoted this argument, then all users are load 810 // instructions (or GEPs with only load users), and all loads should be 811 // using the new argument that we added. 812 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 813 814 while (!I->use_empty()) { 815 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 816 assert(ArgIndices.begin()->empty() && 817 "Load element should sort to front!"); 818 I2->setName(I->getName()+".val"); 819 LI->replaceAllUsesWith(I2); 820 AA.replaceWithNewValue(LI, I2); 821 LI->eraseFromParent(); 822 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName() 823 << "' in function '" << F->getName() << "'\n"); 824 } else { 825 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 826 IndicesVector Operands; 827 Operands.reserve(GEP->getNumIndices()); 828 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 829 II != IE; ++II) 830 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); 831 832 // GEPs with a single 0 index can be merged with direct loads 833 if (Operands.size() == 1 && Operands.front() == 0) 834 Operands.clear(); 835 836 Function::arg_iterator TheArg = I2; 837 for (ScalarizeTable::iterator It = ArgIndices.begin(); 838 *It != Operands; ++It, ++TheArg) { 839 assert(It != ArgIndices.end() && "GEP not handled??"); 840 } 841 842 std::string NewName = I->getName(); 843 for (unsigned i = 0, e = Operands.size(); i != e; ++i) { 844 NewName += "." + utostr(Operands[i]); 845 } 846 NewName += ".val"; 847 TheArg->setName(NewName); 848 849 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName() 850 << "' of function '" << NF->getName() << "'\n"); 851 852 // All of the uses must be load instructions. Replace them all with 853 // the argument specified by ArgNo. 854 while (!GEP->use_empty()) { 855 LoadInst *L = cast<LoadInst>(GEP->use_back()); 856 L->replaceAllUsesWith(TheArg); 857 AA.replaceWithNewValue(L, TheArg); 858 L->eraseFromParent(); 859 } 860 AA.deleteValue(GEP); 861 GEP->eraseFromParent(); 862 } 863 } 864 865 // Increment I2 past all of the arguments added for this promoted pointer. 866 for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i) 867 ++I2; 868 } 869 870 // Notify the alias analysis implementation that we inserted a new argument. 871 if (ExtraArgHack) 872 AA.copyValue(Constant::getNullValue(Type::getInt32Ty(F->getContext())), 873 NF->arg_begin()); 874 875 876 // Tell the alias analysis that the old function is about to disappear. 877 AA.replaceWithNewValue(F, NF); 878 879 880 NF_CGN->stealCalledFunctionsFrom(CG[F]); 881 882 // Now that the old function is dead, delete it. If there is a dangling 883 // reference to the CallgraphNode, just leave the dead function around for 884 // someone else to nuke. 885 CallGraphNode *CGN = CG[F]; 886 if (CGN->getNumReferences() == 0) 887 delete CG.removeFunctionFromModule(CGN); 888 else 889 F->setLinkage(Function::ExternalLinkage); 890 891 return NF_CGN; 892} 893