ArgumentPromotion.cpp revision 5095e3d1d1caef8d573534d369e37277c623064c
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/Compiler.h" 45#include "llvm/Support/CFG.h" 46#include "llvm/Support/Debug.h" 47#include "llvm/Support/raw_ostream.h" 48#include "llvm/ADT/DepthFirstIterator.h" 49#include "llvm/ADT/Statistic.h" 50#include "llvm/ADT/StringExtras.h" 51#include <set> 52using namespace llvm; 53 54STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted"); 55STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted"); 56STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted"); 57STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated"); 58 59namespace { 60 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass. 61 /// 62 struct VISIBILITY_HIDDEN ArgPromotion : public CallGraphSCCPass { 63 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 64 AU.addRequired<AliasAnalysis>(); 65 CallGraphSCCPass::getAnalysisUsage(AU); 66 } 67 68 virtual bool runOnSCC(std::vector<CallGraphNode *> &SCC); 69 static char ID; // Pass identification, replacement for typeid 70 explicit ArgPromotion(unsigned maxElements = 3) 71 : CallGraphSCCPass(&ID), maxElements(maxElements) {} 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; 88static RegisterPass<ArgPromotion> 89X("argpromotion", "Promote 'by reference' arguments to scalars"); 90 91Pass *llvm::createArgumentPromotionPass(unsigned maxElements) { 92 return new ArgPromotion(maxElements); 93} 94 95bool ArgPromotion::runOnSCC(std::vector<CallGraphNode *> &SCC) { 96 bool Changed = false, LocalChange; 97 98 do { // Iterate until we stop promoting from this SCC. 99 LocalChange = false; 100 // Attempt to promote arguments from all functions in this SCC. 101 for (unsigned i = 0, e = SCC.size(); i != e; ++i) 102 if (CallGraphNode *CGN = PromoteArguments(SCC[i])) { 103 LocalChange = true; 104 SCC[i] = CGN; 105 } 106 Changed |= LocalChange; // Remember that we changed something. 107 } while (LocalChange); 108 109 return Changed; 110} 111 112/// PromoteArguments - This method checks the specified function to see if there 113/// are any promotable arguments and if it is safe to promote the function (for 114/// example, all callers are direct). If safe to promote some arguments, it 115/// calls the DoPromotion method. 116/// 117CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) { 118 Function *F = CGN->getFunction(); 119 120 // Make sure that it is local to this module. 121 if (!F || !F->hasLocalLinkage()) return 0; 122 123 // First check: see if there are any pointer arguments! If not, quick exit. 124 SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs; 125 unsigned ArgNo = 0; 126 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 127 I != E; ++I, ++ArgNo) 128 if (isa<PointerType>(I->getType())) 129 PointerArgs.push_back(std::pair<Argument*, unsigned>(I, ArgNo)); 130 if (PointerArgs.empty()) return 0; 131 132 // Second check: make sure that all callers are direct callers. We can't 133 // transform functions that have indirect callers. 134 if (F->hasAddressTaken()) 135 return 0; 136 137 // Check to see which arguments are promotable. If an argument is promotable, 138 // add it to ArgsToPromote. 139 SmallPtrSet<Argument*, 8> ArgsToPromote; 140 SmallPtrSet<Argument*, 8> ByValArgsToTransform; 141 for (unsigned i = 0; i != PointerArgs.size(); ++i) { 142 bool isByVal = F->paramHasAttr(PointerArgs[i].second+1, Attribute::ByVal); 143 144 // If this is a byval argument, and if the aggregate type is small, just 145 // pass the elements, which is always safe. 146 Argument *PtrArg = PointerArgs[i].first; 147 if (isByVal) { 148 const Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType(); 149 if (const StructType *STy = dyn_cast<StructType>(AgTy)) { 150 if (maxElements > 0 && STy->getNumElements() > maxElements) { 151 DEBUG(errs() << "argpromotion disable promoting argument '" 152 << PtrArg->getName() << "' because it would require adding more" 153 << " than " << maxElements << " arguments to the function.\n"); 154 } else { 155 // If all the elements are single-value types, we can promote it. 156 bool AllSimple = true; 157 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 158 if (!STy->getElementType(i)->isSingleValueType()) { 159 AllSimple = false; 160 break; 161 } 162 163 // Safe to transform, don't even bother trying to "promote" it. 164 // Passing the elements as a scalar will allow scalarrepl to hack on 165 // the new alloca we introduce. 166 if (AllSimple) { 167 ByValArgsToTransform.insert(PtrArg); 168 continue; 169 } 170 } 171 } 172 } 173 174 // Otherwise, see if we can promote the pointer to its value. 175 if (isSafeToPromoteArgument(PtrArg, isByVal)) 176 ArgsToPromote.insert(PtrArg); 177 } 178 179 // No promotable pointer arguments. 180 if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) 181 return 0; 182 183 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform); 184} 185 186/// IsAlwaysValidPointer - Return true if the specified pointer is always legal 187/// to load. 188static bool IsAlwaysValidPointer(Value *V) { 189 if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true; 190 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) 191 return IsAlwaysValidPointer(GEP->getOperand(0)); 192 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 193 if (CE->getOpcode() == Instruction::GetElementPtr) 194 return IsAlwaysValidPointer(CE->getOperand(0)); 195 196 return false; 197} 198 199/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that 200/// all callees pass in a valid pointer for the specified function argument. 201static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) { 202 Function *Callee = Arg->getParent(); 203 204 unsigned ArgNo = std::distance(Callee->arg_begin(), 205 Function::arg_iterator(Arg)); 206 207 // Look at all call sites of the function. At this pointer we know we only 208 // have direct callees. 209 for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end(); 210 UI != E; ++UI) { 211 CallSite CS = CallSite::get(*UI); 212 assert(CS.getInstruction() && "Should only have direct calls!"); 213 214 if (!IsAlwaysValidPointer(CS.getArgument(ArgNo))) 215 return false; 216 } 217 return true; 218} 219 220/// Returns true if Prefix is a prefix of longer. That means, Longer has a size 221/// that is greater than or equal to the size of prefix, and each of the 222/// elements in Prefix is the same as the corresponding elements in Longer. 223/// 224/// This means it also returns true when Prefix and Longer are equal! 225static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix, 226 const ArgPromotion::IndicesVector &Longer) { 227 if (Prefix.size() > Longer.size()) 228 return false; 229 for (unsigned i = 0, e = Prefix.size(); i != e; ++i) 230 if (Prefix[i] != Longer[i]) 231 return false; 232 return true; 233} 234 235 236/// Checks if Indices, or a prefix of Indices, is in Set. 237static bool PrefixIn(const ArgPromotion::IndicesVector &Indices, 238 std::set<ArgPromotion::IndicesVector> &Set) { 239 std::set<ArgPromotion::IndicesVector>::iterator Low; 240 Low = Set.upper_bound(Indices); 241 if (Low != Set.begin()) 242 Low--; 243 // Low is now the last element smaller than or equal to Indices. This means 244 // it points to a prefix of Indices (possibly Indices itself), if such 245 // prefix exists. 246 // 247 // This load is safe if any prefix of its operands is safe to load. 248 return Low != Set.end() && IsPrefix(*Low, Indices); 249} 250 251/// Mark the given indices (ToMark) as safe in the the given set of indices 252/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there 253/// is already a prefix of Indices in Safe, Indices are implicitely marked safe 254/// already. Furthermore, any indices that Indices is itself a prefix of, are 255/// removed from Safe (since they are implicitely safe because of Indices now). 256static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark, 257 std::set<ArgPromotion::IndicesVector> &Safe) { 258 std::set<ArgPromotion::IndicesVector>::iterator Low; 259 Low = Safe.upper_bound(ToMark); 260 // Guard against the case where Safe is empty 261 if (Low != Safe.begin()) 262 Low--; 263 // Low is now the last element smaller than or equal to Indices. This 264 // means it points to a prefix of Indices (possibly Indices itself), if 265 // such prefix exists. 266 if (Low != Safe.end()) { 267 if (IsPrefix(*Low, ToMark)) 268 // If there is already a prefix of these indices (or exactly these 269 // indices) marked a safe, don't bother adding these indices 270 return; 271 272 // Increment Low, so we can use it as a "insert before" hint 273 ++Low; 274 } 275 // Insert 276 Low = Safe.insert(Low, ToMark); 277 ++Low; 278 // If there we're a prefix of longer index list(s), remove those 279 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end(); 280 while (Low != End && IsPrefix(ToMark, *Low)) { 281 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low; 282 ++Low; 283 Safe.erase(Remove); 284 } 285} 286 287/// isSafeToPromoteArgument - As you might guess from the name of this method, 288/// it checks to see if it is both safe and useful to promote the argument. 289/// This method limits promotion of aggregates to only promote up to three 290/// elements of the aggregate in order to avoid exploding the number of 291/// arguments passed in. 292bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { 293 typedef std::set<IndicesVector> GEPIndicesSet; 294 295 // Quick exit for unused arguments 296 if (Arg->use_empty()) 297 return true; 298 299 // We can only promote this argument if all of the uses are loads, or are GEP 300 // instructions (with constant indices) that are subsequently loaded. 301 // 302 // Promoting the argument causes it to be loaded in the caller 303 // unconditionally. This is only safe if we can prove that either the load 304 // would have happened in the callee anyway (ie, there is a load in the entry 305 // block) or the pointer passed in at every call site is guaranteed to be 306 // valid. 307 // In the former case, invalid loads can happen, but would have happened 308 // anyway, in the latter case, invalid loads won't happen. This prevents us 309 // from introducing an invalid load that wouldn't have happened in the 310 // original code. 311 // 312 // This set will contain all sets of indices that are loaded in the entry 313 // block, and thus are safe to unconditionally load in the caller. 314 GEPIndicesSet SafeToUnconditionallyLoad; 315 316 // This set contains all the sets of indices that we are planning to promote. 317 // This makes it possible to limit the number of arguments added. 318 GEPIndicesSet ToPromote; 319 320 // If the pointer is always valid, any load with first index 0 is valid. 321 if(isByVal || AllCalleesPassInValidPointerForArgument(Arg)) 322 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); 323 324 // First, iterate the entry block and mark loads of (geps of) arguments as 325 // safe. 326 BasicBlock *EntryBlock = Arg->getParent()->begin(); 327 // Declare this here so we can reuse it 328 IndicesVector Indices; 329 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end(); 330 I != E; ++I) 331 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 332 Value *V = LI->getPointerOperand(); 333 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { 334 V = GEP->getPointerOperand(); 335 if (V == Arg) { 336 // This load actually loads (part of) Arg? Check the indices then. 337 Indices.reserve(GEP->getNumIndices()); 338 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 339 II != IE; ++II) 340 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) 341 Indices.push_back(CI->getSExtValue()); 342 else 343 // We found a non-constant GEP index for this argument? Bail out 344 // right away, can't promote this argument at all. 345 return false; 346 347 // Indices checked out, mark them as safe 348 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); 349 Indices.clear(); 350 } 351 } else if (V == Arg) { 352 // Direct loads are equivalent to a GEP with a single 0 index. 353 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); 354 } 355 } 356 357 // Now, iterate all uses of the argument to see if there are any uses that are 358 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. 359 SmallVector<LoadInst*, 16> Loads; 360 IndicesVector Operands; 361 for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); 362 UI != E; ++UI) { 363 Operands.clear(); 364 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 365 if (LI->isVolatile()) return false; // Don't hack volatile loads 366 Loads.push_back(LI); 367 // Direct loads are equivalent to a GEP with a zero index and then a load. 368 Operands.push_back(0); 369 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) { 370 if (GEP->use_empty()) { 371 // Dead GEP's cause trouble later. Just remove them if we run into 372 // them. 373 getAnalysis<AliasAnalysis>().deleteValue(GEP); 374 GEP->eraseFromParent(); 375 // TODO: This runs the above loop over and over again for dead GEPS 376 // Couldn't we just do increment the UI iterator earlier and erase the 377 // use? 378 return isSafeToPromoteArgument(Arg, isByVal); 379 } 380 381 // Ensure that all of the indices are constants. 382 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); 383 i != e; ++i) 384 if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) 385 Operands.push_back(C->getSExtValue()); 386 else 387 return false; // Not a constant operand GEP! 388 389 // Ensure that the only users of the GEP are load instructions. 390 for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); 391 UI != E; ++UI) 392 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 393 if (LI->isVolatile()) return false; // Don't hack volatile loads 394 Loads.push_back(LI); 395 } else { 396 // Other uses than load? 397 return false; 398 } 399 } else { 400 return false; // Not a load or a GEP. 401 } 402 403 // Now, see if it is safe to promote this load / loads of this GEP. Loading 404 // is safe if Operands, or a prefix of Operands, is marked as safe. 405 if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) 406 return false; 407 408 // See if we are already promoting a load with these indices. If not, check 409 // to make sure that we aren't promoting too many elements. If so, nothing 410 // to do. 411 if (ToPromote.find(Operands) == ToPromote.end()) { 412 if (maxElements > 0 && ToPromote.size() == maxElements) { 413 DEBUG(errs() << "argpromotion not promoting argument '" 414 << Arg->getName() << "' because it would require adding more " 415 << "than " << maxElements << " arguments to the function.\n"); 416 // We limit aggregate promotion to only promoting up to a fixed number 417 // of elements of the aggregate. 418 return false; 419 } 420 ToPromote.insert(Operands); 421 } 422 } 423 424 if (Loads.empty()) return true; // No users, this is a dead argument. 425 426 // Okay, now we know that the argument is only used by load instructions and 427 // it is safe to unconditionally perform all of them. Use alias analysis to 428 // check to see if the pointer is guaranteed to not be modified from entry of 429 // the function to each of the load instructions. 430 431 // Because there could be several/many load instructions, remember which 432 // blocks we know to be transparent to the load. 433 SmallPtrSet<BasicBlock*, 16> TranspBlocks; 434 435 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 436 TargetData *TD = getAnalysisIfAvailable<TargetData>(); 437 if (!TD) return false; // Without TargetData, assume the worst. 438 439 for (unsigned i = 0, e = Loads.size(); i != e; ++i) { 440 // Check to see if the load is invalidated from the start of the block to 441 // the load itself. 442 LoadInst *Load = Loads[i]; 443 BasicBlock *BB = Load->getParent(); 444 445 const PointerType *LoadTy = 446 cast<PointerType>(Load->getPointerOperand()->getType()); 447 unsigned LoadSize =(unsigned)TD->getTypeStoreSize(LoadTy->getElementType()); 448 449 if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize)) 450 return false; // Pointer is invalidated! 451 452 // Now check every path from the entry block to the load for transparency. 453 // To do this, we perform a depth first search on the inverse CFG from the 454 // loading block. 455 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 456 for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> > 457 I = idf_ext_begin(*PI, TranspBlocks), 458 E = idf_ext_end(*PI, TranspBlocks); I != E; ++I) 459 if (AA.canBasicBlockModify(**I, Arg, LoadSize)) 460 return false; 461 } 462 463 // If the path from the entry of the function to each load is free of 464 // instructions that potentially invalidate the load, we can make the 465 // transformation! 466 return true; 467} 468 469/// DoPromotion - This method actually performs the promotion of the specified 470/// arguments, and returns the new function. At this point, we know that it's 471/// safe to do so. 472CallGraphNode *ArgPromotion::DoPromotion(Function *F, 473 SmallPtrSet<Argument*, 8> &ArgsToPromote, 474 SmallPtrSet<Argument*, 8> &ByValArgsToTransform) { 475 476 // Start by computing a new prototype for the function, which is the same as 477 // the old function, but has modified arguments. 478 const FunctionType *FTy = F->getFunctionType(); 479 std::vector<const Type*> Params; 480 481 typedef std::set<IndicesVector> ScalarizeTable; 482 483 // ScalarizedElements - If we are promoting a pointer that has elements 484 // accessed out of it, keep track of which elements are accessed so that we 485 // can add one argument for each. 486 // 487 // Arguments that are directly loaded will have a zero element value here, to 488 // handle cases where there are both a direct load and GEP accesses. 489 // 490 std::map<Argument*, ScalarizeTable> ScalarizedElements; 491 492 // OriginalLoads - Keep track of a representative load instruction from the 493 // original function so that we can tell the alias analysis implementation 494 // what the new GEP/Load instructions we are inserting look like. 495 std::map<IndicesVector, LoadInst*> OriginalLoads; 496 497 // Attributes - Keep track of the parameter attributes for the arguments 498 // that we are *not* promoting. For the ones that we do promote, the parameter 499 // attributes are lost 500 SmallVector<AttributeWithIndex, 8> AttributesVec; 501 const AttrListPtr &PAL = F->getAttributes(); 502 503 // Add any return attributes. 504 if (Attributes attrs = PAL.getRetAttributes()) 505 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 506 507 // First, determine the new argument list 508 unsigned ArgIndex = 1; 509 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; 510 ++I, ++ArgIndex) { 511 if (ByValArgsToTransform.count(I)) { 512 // Simple byval argument? Just add all the struct element types. 513 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 514 const StructType *STy = cast<StructType>(AgTy); 515 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 516 Params.push_back(STy->getElementType(i)); 517 ++NumByValArgsPromoted; 518 } else if (!ArgsToPromote.count(I)) { 519 // Unchanged argument 520 Params.push_back(I->getType()); 521 if (Attributes attrs = PAL.getParamAttributes(ArgIndex)) 522 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), attrs)); 523 } else if (I->use_empty()) { 524 // Dead argument (which are always marked as promotable) 525 ++NumArgumentsDead; 526 } else { 527 // Okay, this is being promoted. This means that the only uses are loads 528 // or GEPs which are only used by loads 529 530 // In this table, we will track which indices are loaded from the argument 531 // (where direct loads are tracked as no indices). 532 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 533 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; 534 ++UI) { 535 Instruction *User = cast<Instruction>(*UI); 536 assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User)); 537 IndicesVector Indices; 538 Indices.reserve(User->getNumOperands() - 1); 539 // Since loads will only have a single operand, and GEPs only a single 540 // non-index operand, this will record direct loads without any indices, 541 // and gep+loads with the GEP indices. 542 for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end(); 543 II != IE; ++II) 544 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue()); 545 // GEPs with a single 0 index can be merged with direct loads 546 if (Indices.size() == 1 && Indices.front() == 0) 547 Indices.clear(); 548 ArgIndices.insert(Indices); 549 LoadInst *OrigLoad; 550 if (LoadInst *L = dyn_cast<LoadInst>(User)) 551 OrigLoad = L; 552 else 553 // Take any load, we will use it only to update Alias Analysis 554 OrigLoad = cast<LoadInst>(User->use_back()); 555 OriginalLoads[Indices] = OrigLoad; 556 } 557 558 // Add a parameter to the function for each element passed in. 559 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 560 E = ArgIndices.end(); SI != E; ++SI) { 561 // not allowed to dereference ->begin() if size() is 0 562 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), 563 SI->begin(), 564 SI->end())); 565 assert(Params.back()); 566 } 567 568 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty()) 569 ++NumArgumentsPromoted; 570 else 571 ++NumAggregatesPromoted; 572 } 573 } 574 575 // Add any function attributes. 576 if (Attributes attrs = PAL.getFnAttributes()) 577 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 578 579 const Type *RetTy = FTy->getReturnType(); 580 581 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 582 // have zero fixed arguments. 583 bool ExtraArgHack = false; 584 if (Params.empty() && FTy->isVarArg()) { 585 ExtraArgHack = true; 586 Params.push_back(Type::getInt32Ty(F->getContext())); 587 } 588 589 // Construct the new function type using the new arguments. 590 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); 591 592 // Create the new function body and insert it into the module... 593 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); 594 NF->copyAttributesFrom(F); 595 596 // Recompute the parameter attributes list based on the new arguments for 597 // the function. 598 NF->setAttributes(AttrListPtr::get(AttributesVec.begin(), AttributesVec.end())); 599 AttributesVec.clear(); 600 601 F->getParent()->getFunctionList().insert(F, NF); 602 NF->takeName(F); 603 604 // Get the alias analysis information that we need to update to reflect our 605 // changes. 606 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 607 608 // Get the callgraph information that we need to update to reflect our 609 // changes. 610 CallGraph &CG = getAnalysis<CallGraph>(); 611 612 // Get a new callgraph node for NF. 613 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF); 614 615 616 // Loop over all of the callers of the function, transforming the call sites 617 // to pass in the loaded pointers. 618 // 619 SmallVector<Value*, 16> Args; 620 while (!F->use_empty()) { 621 CallSite CS = CallSite::get(F->use_back()); 622 Instruction *Call = CS.getInstruction(); 623 const AttrListPtr &CallPAL = CS.getAttributes(); 624 625 // Add any return attributes. 626 if (Attributes attrs = CallPAL.getRetAttributes()) 627 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 628 629 // Loop over the operands, inserting GEP and loads in the caller as 630 // appropriate. 631 CallSite::arg_iterator AI = CS.arg_begin(); 632 ArgIndex = 1; 633 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 634 I != E; ++I, ++AI, ++ArgIndex) 635 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 636 Args.push_back(*AI); // Unmodified argument 637 638 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 639 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 640 641 } else if (ByValArgsToTransform.count(I)) { 642 // Emit a GEP and load for each element of the struct. 643 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 644 const StructType *STy = cast<StructType>(AgTy); 645 Value *Idxs[2] = { 646 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 647 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 648 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 649 Value *Idx = GetElementPtrInst::Create(*AI, Idxs, Idxs+2, 650 (*AI)->getName()+"."+utostr(i), 651 Call); 652 // TODO: Tell AA about the new values? 653 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); 654 } 655 } else if (!I->use_empty()) { 656 // Non-dead argument: insert GEPs and loads as appropriate. 657 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 658 // Store the Value* version of the indices in here, but declare it now 659 // for reuse 660 std::vector<Value*> Ops; 661 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 662 E = ArgIndices.end(); SI != E; ++SI) { 663 Value *V = *AI; 664 LoadInst *OrigLoad = OriginalLoads[*SI]; 665 if (!SI->empty()) { 666 Ops.reserve(SI->size()); 667 const Type *ElTy = V->getType(); 668 for (IndicesVector::const_iterator II = SI->begin(), 669 IE = SI->end(); II != IE; ++II) { 670 // Use i32 to index structs, and i64 for others (pointers/arrays). 671 // This satisfies GEP constraints. 672 const Type *IdxTy = (isa<StructType>(ElTy) ? 673 Type::getInt32Ty(F->getContext()) : 674 Type::getInt64Ty(F->getContext())); 675 Ops.push_back(ConstantInt::get(IdxTy, *II)); 676 // Keep track of the type we're currently indexing 677 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II); 678 } 679 // And create a GEP to extract those indices 680 V = GetElementPtrInst::Create(V, Ops.begin(), Ops.end(), 681 V->getName()+".idx", Call); 682 Ops.clear(); 683 AA.copyValue(OrigLoad->getOperand(0), V); 684 } 685 Args.push_back(new LoadInst(V, V->getName()+".val", Call)); 686 AA.copyValue(OrigLoad, Args.back()); 687 } 688 } 689 690 if (ExtraArgHack) 691 Args.push_back(Constant::getNullValue(Type::getInt32Ty(F->getContext()))); 692 693 // Push any varargs arguments on the list 694 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { 695 Args.push_back(*AI); 696 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 697 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 698 } 699 700 // Add any function attributes. 701 if (Attributes attrs = CallPAL.getFnAttributes()) 702 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 703 704 Instruction *New; 705 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 706 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 707 Args.begin(), Args.end(), "", Call); 708 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 709 cast<InvokeInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 710 AttributesVec.end())); 711 } else { 712 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 713 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 714 cast<CallInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 715 AttributesVec.end())); 716 if (cast<CallInst>(Call)->isTailCall()) 717 cast<CallInst>(New)->setTailCall(); 718 } 719 Args.clear(); 720 AttributesVec.clear(); 721 722 // Update the alias analysis implementation to know that we are replacing 723 // the old call with a new one. 724 AA.replaceWithNewValue(Call, New); 725 726 // Update the callgraph to know that the callsite has been transformed. 727 CG[Call->getParent()->getParent()]->replaceCallSite(Call, New, NF_CGN); 728 729 if (!Call->use_empty()) { 730 Call->replaceAllUsesWith(New); 731 New->takeName(Call); 732 } 733 734 // Finally, remove the old call from the program, reducing the use-count of 735 // F. 736 Call->eraseFromParent(); 737 } 738 739 // Since we have now created the new function, splice the body of the old 740 // function right into the new function, leaving the old rotting hulk of the 741 // function empty. 742 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 743 744 // Loop over the argument list, transfering uses of the old arguments over to 745 // the new arguments, also transfering over the names as well. 746 // 747 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 748 I2 = NF->arg_begin(); I != E; ++I) { 749 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 750 // If this is an unmodified argument, move the name and users over to the 751 // new version. 752 I->replaceAllUsesWith(I2); 753 I2->takeName(I); 754 AA.replaceWithNewValue(I, I2); 755 ++I2; 756 continue; 757 } 758 759 if (ByValArgsToTransform.count(I)) { 760 // In the callee, we create an alloca, and store each of the new incoming 761 // arguments into the alloca. 762 Instruction *InsertPt = NF->begin()->begin(); 763 764 // Just add all the struct element types. 765 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 766 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 767 const StructType *STy = cast<StructType>(AgTy); 768 Value *Idxs[2] = { 769 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 770 771 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 772 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 773 Value *Idx = 774 GetElementPtrInst::Create(TheAlloca, Idxs, Idxs+2, 775 TheAlloca->getName()+"."+Twine(i), 776 InsertPt); 777 I2->setName(I->getName()+"."+Twine(i)); 778 new StoreInst(I2++, Idx, InsertPt); 779 } 780 781 // Anything that used the arg should now use the alloca. 782 I->replaceAllUsesWith(TheAlloca); 783 TheAlloca->takeName(I); 784 AA.replaceWithNewValue(I, TheAlloca); 785 continue; 786 } 787 788 if (I->use_empty()) { 789 AA.deleteValue(I); 790 continue; 791 } 792 793 // Otherwise, if we promoted this argument, then all users are load 794 // instructions (or GEPs with only load users), and all loads should be 795 // using the new argument that we added. 796 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 797 798 while (!I->use_empty()) { 799 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 800 assert(ArgIndices.begin()->empty() && 801 "Load element should sort to front!"); 802 I2->setName(I->getName()+".val"); 803 LI->replaceAllUsesWith(I2); 804 AA.replaceWithNewValue(LI, I2); 805 LI->eraseFromParent(); 806 DEBUG(errs() << "*** Promoted load of argument '" << I->getName() 807 << "' in function '" << F->getName() << "'\n"); 808 } else { 809 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 810 IndicesVector Operands; 811 Operands.reserve(GEP->getNumIndices()); 812 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 813 II != IE; ++II) 814 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); 815 816 // GEPs with a single 0 index can be merged with direct loads 817 if (Operands.size() == 1 && Operands.front() == 0) 818 Operands.clear(); 819 820 Function::arg_iterator TheArg = I2; 821 for (ScalarizeTable::iterator It = ArgIndices.begin(); 822 *It != Operands; ++It, ++TheArg) { 823 assert(It != ArgIndices.end() && "GEP not handled??"); 824 } 825 826 std::string NewName = I->getName(); 827 for (unsigned i = 0, e = Operands.size(); i != e; ++i) { 828 NewName += "." + utostr(Operands[i]); 829 } 830 NewName += ".val"; 831 TheArg->setName(NewName); 832 833 DEBUG(errs() << "*** Promoted agg argument '" << TheArg->getName() 834 << "' of function '" << NF->getName() << "'\n"); 835 836 // All of the uses must be load instructions. Replace them all with 837 // the argument specified by ArgNo. 838 while (!GEP->use_empty()) { 839 LoadInst *L = cast<LoadInst>(GEP->use_back()); 840 L->replaceAllUsesWith(TheArg); 841 AA.replaceWithNewValue(L, TheArg); 842 L->eraseFromParent(); 843 } 844 AA.deleteValue(GEP); 845 GEP->eraseFromParent(); 846 } 847 } 848 849 // Increment I2 past all of the arguments added for this promoted pointer. 850 for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i) 851 ++I2; 852 } 853 854 // Notify the alias analysis implementation that we inserted a new argument. 855 if (ExtraArgHack) 856 AA.copyValue(Constant::getNullValue(Type::getInt32Ty(F->getContext())), 857 NF->arg_begin()); 858 859 860 // Tell the alias analysis that the old function is about to disappear. 861 AA.replaceWithNewValue(F, NF); 862 863 864 NF_CGN->stealCalledFunctionsFrom(CG[F]); 865 866 // Now that the old function is dead, delete it. 867 delete CG.removeFunctionFromModule(F); 868 869 return NF_CGN; 870} 871