ArgumentPromotion.cpp revision ce63ffb52f249b62cdf2d250c128007b13f27e71
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 AU.addRequired<TargetData>(); 66 CallGraphSCCPass::getAnalysisUsage(AU); 67 } 68 69 virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCC); 70 static char ID; // Pass identification, replacement for typeid 71 explicit ArgPromotion(unsigned maxElements = 3) 72 : CallGraphSCCPass(&ID), maxElements(maxElements) {} 73 74 /// A vector used to hold the indices of a single GEP instruction 75 typedef std::vector<uint64_t> IndicesVector; 76 77 private: 78 bool PromoteArguments(CallGraphNode *CGN); 79 bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const; 80 Function *DoPromotion(Function *F, 81 SmallPtrSet<Argument*, 8> &ArgsToPromote, 82 SmallPtrSet<Argument*, 8> &ByValArgsToTransform); 83 /// The maximum number of elements to expand, or 0 for unlimited. 84 unsigned maxElements; 85 }; 86} 87 88char ArgPromotion::ID = 0; 89static RegisterPass<ArgPromotion> 90X("argpromotion", "Promote 'by reference' arguments to scalars"); 91 92Pass *llvm::createArgumentPromotionPass(unsigned maxElements) { 93 return new ArgPromotion(maxElements); 94} 95 96bool ArgPromotion::runOnSCC(const std::vector<CallGraphNode *> &SCC) { 97 bool Changed = false, LocalChange; 98 99 do { // Iterate until we stop promoting from this SCC. 100 LocalChange = false; 101 // Attempt to promote arguments from all functions in this SCC. 102 for (unsigned i = 0, e = SCC.size(); i != e; ++i) 103 LocalChange |= PromoteArguments(SCC[i]); 104 Changed |= LocalChange; // Remember that we changed something. 105 } while (LocalChange); 106 107 return Changed; 108} 109 110/// PromoteArguments - This method checks the specified function to see if there 111/// are any promotable arguments and if it is safe to promote the function (for 112/// example, all callers are direct). If safe to promote some arguments, it 113/// calls the DoPromotion method. 114/// 115bool ArgPromotion::PromoteArguments(CallGraphNode *CGN) { 116 Function *F = CGN->getFunction(); 117 118 // Make sure that it is local to this module. 119 if (!F || !F->hasLocalLinkage()) return false; 120 121 // First check: see if there are any pointer arguments! If not, quick exit. 122 SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs; 123 unsigned ArgNo = 0; 124 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 125 I != E; ++I, ++ArgNo) 126 if (isa<PointerType>(I->getType())) 127 PointerArgs.push_back(std::pair<Argument*, unsigned>(I, ArgNo)); 128 if (PointerArgs.empty()) return false; 129 130 // Second check: make sure that all callers are direct callers. We can't 131 // transform functions that have indirect callers. 132 if (F->hasAddressTaken()) 133 return false; 134 135 // Check to see which arguments are promotable. If an argument is promotable, 136 // add it to ArgsToPromote. 137 SmallPtrSet<Argument*, 8> ArgsToPromote; 138 SmallPtrSet<Argument*, 8> ByValArgsToTransform; 139 for (unsigned i = 0; i != PointerArgs.size(); ++i) { 140 bool isByVal = F->paramHasAttr(PointerArgs[i].second+1, Attribute::ByVal); 141 142 // If this is a byval argument, and if the aggregate type is small, just 143 // pass the elements, which is always safe. 144 Argument *PtrArg = PointerArgs[i].first; 145 if (isByVal) { 146 const Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType(); 147 if (const StructType *STy = dyn_cast<StructType>(AgTy)) { 148 if (maxElements > 0 && STy->getNumElements() > maxElements) { 149 DEBUG(errs() << "argpromotion disable promoting argument '" 150 << PtrArg->getName() << "' because it would require adding more" 151 << " than " << maxElements << " arguments to the function.\n"); 152 } else { 153 // If all the elements are single-value types, we can promote it. 154 bool AllSimple = true; 155 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 156 if (!STy->getElementType(i)->isSingleValueType()) { 157 AllSimple = false; 158 break; 159 } 160 161 // Safe to transform, don't even bother trying to "promote" it. 162 // Passing the elements as a scalar will allow scalarrepl to hack on 163 // the new alloca we introduce. 164 if (AllSimple) { 165 ByValArgsToTransform.insert(PtrArg); 166 continue; 167 } 168 } 169 } 170 } 171 172 // Otherwise, see if we can promote the pointer to its value. 173 if (isSafeToPromoteArgument(PtrArg, isByVal)) 174 ArgsToPromote.insert(PtrArg); 175 } 176 177 // No promotable pointer arguments. 178 if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) return false; 179 180 Function *NewF = DoPromotion(F, ArgsToPromote, ByValArgsToTransform); 181 182 // Update the call graph to know that the function has been transformed. 183 getAnalysis<CallGraph>().changeFunction(F, NewF); 184 return true; 185} 186 187/// IsAlwaysValidPointer - Return true if the specified pointer is always legal 188/// to load. 189static bool IsAlwaysValidPointer(Value *V) { 190 if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true; 191 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) 192 return IsAlwaysValidPointer(GEP->getOperand(0)); 193 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 194 if (CE->getOpcode() == Instruction::GetElementPtr) 195 return IsAlwaysValidPointer(CE->getOperand(0)); 196 197 return false; 198} 199 200/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that 201/// all callees pass in a valid pointer for the specified function argument. 202static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) { 203 Function *Callee = Arg->getParent(); 204 205 unsigned ArgNo = std::distance(Callee->arg_begin(), 206 Function::arg_iterator(Arg)); 207 208 // Look at all call sites of the function. At this pointer we know we only 209 // have direct callees. 210 for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end(); 211 UI != E; ++UI) { 212 CallSite CS = CallSite::get(*UI); 213 assert(CS.getInstruction() && "Should only have direct calls!"); 214 215 if (!IsAlwaysValidPointer(CS.getArgument(ArgNo))) 216 return false; 217 } 218 return true; 219} 220 221/// Returns true if Prefix is a prefix of longer. That means, Longer has a size 222/// that is greater than or equal to the size of prefix, and each of the 223/// elements in Prefix is the same as the corresponding elements in Longer. 224/// 225/// This means it also returns true when Prefix and Longer are equal! 226static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix, 227 const ArgPromotion::IndicesVector &Longer) { 228 if (Prefix.size() > Longer.size()) 229 return false; 230 for (unsigned i = 0, e = Prefix.size(); i != e; ++i) 231 if (Prefix[i] != Longer[i]) 232 return false; 233 return true; 234} 235 236 237/// Checks if Indices, or a prefix of Indices, is in Set. 238static bool PrefixIn(const ArgPromotion::IndicesVector &Indices, 239 std::set<ArgPromotion::IndicesVector> &Set) { 240 std::set<ArgPromotion::IndicesVector>::iterator Low; 241 Low = Set.upper_bound(Indices); 242 if (Low != Set.begin()) 243 Low--; 244 // Low is now the last element smaller than or equal to Indices. This means 245 // it points to a prefix of Indices (possibly Indices itself), if such 246 // prefix exists. 247 // 248 // This load is safe if any prefix of its operands is safe to load. 249 return Low != Set.end() && IsPrefix(*Low, Indices); 250} 251 252/// Mark the given indices (ToMark) as safe in the the given set of indices 253/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there 254/// is already a prefix of Indices in Safe, Indices are implicitely marked safe 255/// already. Furthermore, any indices that Indices is itself a prefix of, are 256/// removed from Safe (since they are implicitely safe because of Indices now). 257static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark, 258 std::set<ArgPromotion::IndicesVector> &Safe) { 259 std::set<ArgPromotion::IndicesVector>::iterator Low; 260 Low = Safe.upper_bound(ToMark); 261 // Guard against the case where Safe is empty 262 if (Low != Safe.begin()) 263 Low--; 264 // Low is now the last element smaller than or equal to Indices. This 265 // means it points to a prefix of Indices (possibly Indices itself), if 266 // such prefix exists. 267 if (Low != Safe.end()) { 268 if (IsPrefix(*Low, ToMark)) 269 // If there is already a prefix of these indices (or exactly these 270 // indices) marked a safe, don't bother adding these indices 271 return; 272 273 // Increment Low, so we can use it as a "insert before" hint 274 ++Low; 275 } 276 // Insert 277 Low = Safe.insert(Low, ToMark); 278 ++Low; 279 // If there we're a prefix of longer index list(s), remove those 280 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end(); 281 while (Low != End && IsPrefix(ToMark, *Low)) { 282 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low; 283 ++Low; 284 Safe.erase(Remove); 285 } 286} 287 288/// isSafeToPromoteArgument - As you might guess from the name of this method, 289/// it checks to see if it is both safe and useful to promote the argument. 290/// This method limits promotion of aggregates to only promote up to three 291/// elements of the aggregate in order to avoid exploding the number of 292/// arguments passed in. 293bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { 294 typedef std::set<IndicesVector> GEPIndicesSet; 295 296 // Quick exit for unused arguments 297 if (Arg->use_empty()) 298 return true; 299 300 // We can only promote this argument if all of the uses are loads, or are GEP 301 // instructions (with constant indices) that are subsequently loaded. 302 // 303 // Promoting the argument causes it to be loaded in the caller 304 // unconditionally. This is only safe if we can prove that either the load 305 // would have happened in the callee anyway (ie, there is a load in the entry 306 // block) or the pointer passed in at every call site is guaranteed to be 307 // valid. 308 // In the former case, invalid loads can happen, but would have happened 309 // anyway, in the latter case, invalid loads won't happen. This prevents us 310 // from introducing an invalid load that wouldn't have happened in the 311 // original code. 312 // 313 // This set will contain all sets of indices that are loaded in the entry 314 // block, and thus are safe to unconditionally load in the caller. 315 GEPIndicesSet SafeToUnconditionallyLoad; 316 317 // This set contains all the sets of indices that we are planning to promote. 318 // This makes it possible to limit the number of arguments added. 319 GEPIndicesSet ToPromote; 320 321 // If the pointer is always valid, any load with first index 0 is valid. 322 if(isByVal || AllCalleesPassInValidPointerForArgument(Arg)) 323 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); 324 325 // First, iterate the entry block and mark loads of (geps of) arguments as 326 // safe. 327 BasicBlock *EntryBlock = Arg->getParent()->begin(); 328 // Declare this here so we can reuse it 329 IndicesVector Indices; 330 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end(); 331 I != E; ++I) 332 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 333 Value *V = LI->getPointerOperand(); 334 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { 335 V = GEP->getPointerOperand(); 336 if (V == Arg) { 337 // This load actually loads (part of) Arg? Check the indices then. 338 Indices.reserve(GEP->getNumIndices()); 339 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 340 II != IE; ++II) 341 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) 342 Indices.push_back(CI->getSExtValue()); 343 else 344 // We found a non-constant GEP index for this argument? Bail out 345 // right away, can't promote this argument at all. 346 return false; 347 348 // Indices checked out, mark them as safe 349 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); 350 Indices.clear(); 351 } 352 } else if (V == Arg) { 353 // Direct loads are equivalent to a GEP with a single 0 index. 354 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); 355 } 356 } 357 358 // Now, iterate all uses of the argument to see if there are any uses that are 359 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. 360 SmallVector<LoadInst*, 16> Loads; 361 IndicesVector Operands; 362 for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); 363 UI != E; ++UI) { 364 Operands.clear(); 365 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 366 if (LI->isVolatile()) return false; // Don't hack volatile loads 367 Loads.push_back(LI); 368 // Direct loads are equivalent to a GEP with a zero index and then a load. 369 Operands.push_back(0); 370 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) { 371 if (GEP->use_empty()) { 372 // Dead GEP's cause trouble later. Just remove them if we run into 373 // them. 374 getAnalysis<AliasAnalysis>().deleteValue(GEP); 375 GEP->eraseFromParent(); 376 // TODO: This runs the above loop over and over again for dead GEPS 377 // Couldn't we just do increment the UI iterator earlier and erase the 378 // use? 379 return isSafeToPromoteArgument(Arg, isByVal); 380 } 381 382 // Ensure that all of the indices are constants. 383 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); 384 i != e; ++i) 385 if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) 386 Operands.push_back(C->getSExtValue()); 387 else 388 return false; // Not a constant operand GEP! 389 390 // Ensure that the only users of the GEP are load instructions. 391 for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); 392 UI != E; ++UI) 393 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 394 if (LI->isVolatile()) return false; // Don't hack volatile loads 395 Loads.push_back(LI); 396 } else { 397 // Other uses than load? 398 return false; 399 } 400 } else { 401 return false; // Not a load or a GEP. 402 } 403 404 // Now, see if it is safe to promote this load / loads of this GEP. Loading 405 // is safe if Operands, or a prefix of Operands, is marked as safe. 406 if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) 407 return false; 408 409 // See if we are already promoting a load with these indices. If not, check 410 // to make sure that we aren't promoting too many elements. If so, nothing 411 // to do. 412 if (ToPromote.find(Operands) == ToPromote.end()) { 413 if (maxElements > 0 && ToPromote.size() == maxElements) { 414 DEBUG(errs() << "argpromotion not promoting argument '" 415 << Arg->getName() << "' because it would require adding more " 416 << "than " << maxElements << " arguments to the function.\n"); 417 // We limit aggregate promotion to only promoting up to a fixed number 418 // of elements of the aggregate. 419 return false; 420 } 421 ToPromote.insert(Operands); 422 } 423 } 424 425 if (Loads.empty()) return true; // No users, this is a dead argument. 426 427 // Okay, now we know that the argument is only used by load instructions and 428 // it is safe to unconditionally perform all of them. Use alias analysis to 429 // check to see if the pointer is guaranteed to not be modified from entry of 430 // the function to each of the load instructions. 431 432 // Because there could be several/many load instructions, remember which 433 // blocks we know to be transparent to the load. 434 SmallPtrSet<BasicBlock*, 16> TranspBlocks; 435 436 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 437 TargetData &TD = getAnalysis<TargetData>(); 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. 472Function *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 LLVMContext &Context = RetTy->getContext(); 581 582 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 583 // have zero fixed arguments. 584 bool ExtraArgHack = false; 585 if (Params.empty() && FTy->isVarArg()) { 586 ExtraArgHack = true; 587 Params.push_back(Type::Int32Ty); 588 } 589 590 // Construct the new function type using the new arguments. 591 FunctionType *NFTy = Context.getFunctionType(RetTy, Params, FTy->isVarArg()); 592 593 // Create the new function body and insert it into the module... 594 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); 595 NF->copyAttributesFrom(F); 596 597 // Recompute the parameter attributes list based on the new arguments for 598 // the function. 599 NF->setAttributes(AttrListPtr::get(AttributesVec.begin(), AttributesVec.end())); 600 AttributesVec.clear(); 601 602 F->getParent()->getFunctionList().insert(F, NF); 603 NF->takeName(F); 604 605 // Get the alias analysis information that we need to update to reflect our 606 // changes. 607 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 608 609 // Get the callgraph information that we need to update to reflect our 610 // changes. 611 CallGraph &CG = getAnalysis<CallGraph>(); 612 613 // Loop over all of the callers of the function, transforming the call sites 614 // to pass in the loaded pointers. 615 // 616 SmallVector<Value*, 16> Args; 617 while (!F->use_empty()) { 618 CallSite CS = CallSite::get(F->use_back()); 619 Instruction *Call = CS.getInstruction(); 620 const AttrListPtr &CallPAL = CS.getAttributes(); 621 622 // Add any return attributes. 623 if (Attributes attrs = CallPAL.getRetAttributes()) 624 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 625 626 // Loop over the operands, inserting GEP and loads in the caller as 627 // appropriate. 628 CallSite::arg_iterator AI = CS.arg_begin(); 629 ArgIndex = 1; 630 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 631 I != E; ++I, ++AI, ++ArgIndex) 632 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 633 Args.push_back(*AI); // Unmodified argument 634 635 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 636 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 637 638 } else if (ByValArgsToTransform.count(I)) { 639 // Emit a GEP and load for each element of the struct. 640 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 641 const StructType *STy = cast<StructType>(AgTy); 642 Value *Idxs[2] = { ConstantInt::get(Type::Int32Ty, 0), 0 }; 643 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 644 Idxs[1] = ConstantInt::get(Type::Int32Ty, i); 645 Value *Idx = GetElementPtrInst::Create(*AI, Idxs, Idxs+2, 646 (*AI)->getName()+"."+utostr(i), 647 Call); 648 // TODO: Tell AA about the new values? 649 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); 650 } 651 } else if (!I->use_empty()) { 652 // Non-dead argument: insert GEPs and loads as appropriate. 653 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 654 // Store the Value* version of the indices in here, but declare it now 655 // for reuse 656 std::vector<Value*> Ops; 657 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 658 E = ArgIndices.end(); SI != E; ++SI) { 659 Value *V = *AI; 660 LoadInst *OrigLoad = OriginalLoads[*SI]; 661 if (!SI->empty()) { 662 Ops.reserve(SI->size()); 663 const Type *ElTy = V->getType(); 664 for (IndicesVector::const_iterator II = SI->begin(), 665 IE = SI->end(); II != IE; ++II) { 666 // Use i32 to index structs, and i64 for others (pointers/arrays). 667 // This satisfies GEP constraints. 668 const Type *IdxTy = (isa<StructType>(ElTy) ? Type::Int32Ty : Type::Int64Ty); 669 Ops.push_back(ConstantInt::get(IdxTy, *II)); 670 // Keep track of the type we're currently indexing 671 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II); 672 } 673 // And create a GEP to extract those indices 674 V = GetElementPtrInst::Create(V, Ops.begin(), Ops.end(), 675 V->getName()+".idx", Call); 676 Ops.clear(); 677 AA.copyValue(OrigLoad->getOperand(0), V); 678 } 679 Args.push_back(new LoadInst(V, V->getName()+".val", Call)); 680 AA.copyValue(OrigLoad, Args.back()); 681 } 682 } 683 684 if (ExtraArgHack) 685 Args.push_back(Context.getNullValue(Type::Int32Ty)); 686 687 // Push any varargs arguments on the list 688 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { 689 Args.push_back(*AI); 690 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 691 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 692 } 693 694 // Add any function attributes. 695 if (Attributes attrs = CallPAL.getFnAttributes()) 696 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 697 698 Instruction *New; 699 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 700 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 701 Args.begin(), Args.end(), "", Call); 702 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 703 cast<InvokeInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 704 AttributesVec.end())); 705 } else { 706 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 707 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 708 cast<CallInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 709 AttributesVec.end())); 710 if (cast<CallInst>(Call)->isTailCall()) 711 cast<CallInst>(New)->setTailCall(); 712 } 713 Args.clear(); 714 AttributesVec.clear(); 715 716 // Update the alias analysis implementation to know that we are replacing 717 // the old call with a new one. 718 AA.replaceWithNewValue(Call, New); 719 720 // Update the callgraph to know that the callsite has been transformed. 721 CG[Call->getParent()->getParent()]->replaceCallSite(Call, New); 722 723 if (!Call->use_empty()) { 724 Call->replaceAllUsesWith(New); 725 New->takeName(Call); 726 } 727 728 // Finally, remove the old call from the program, reducing the use-count of 729 // F. 730 Call->eraseFromParent(); 731 } 732 733 // Since we have now created the new function, splice the body of the old 734 // function right into the new function, leaving the old rotting hulk of the 735 // function empty. 736 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 737 738 // Loop over the argument list, transfering uses of the old arguments over to 739 // the new arguments, also transfering over the names as well. 740 // 741 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 742 I2 = NF->arg_begin(); I != E; ++I) { 743 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 744 // If this is an unmodified argument, move the name and users over to the 745 // new version. 746 I->replaceAllUsesWith(I2); 747 I2->takeName(I); 748 AA.replaceWithNewValue(I, I2); 749 ++I2; 750 continue; 751 } 752 753 if (ByValArgsToTransform.count(I)) { 754 // In the callee, we create an alloca, and store each of the new incoming 755 // arguments into the alloca. 756 Instruction *InsertPt = NF->begin()->begin(); 757 758 // Just add all the struct element types. 759 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 760 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 761 const StructType *STy = cast<StructType>(AgTy); 762 Value *Idxs[2] = { ConstantInt::get(Type::Int32Ty, 0), 0 }; 763 764 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 765 Idxs[1] = ConstantInt::get(Type::Int32Ty, i); 766 Value *Idx = 767 GetElementPtrInst::Create(TheAlloca, Idxs, Idxs+2, 768 TheAlloca->getName()+"."+utostr(i), 769 InsertPt); 770 I2->setName(I->getName()+"."+utostr(i)); 771 new StoreInst(I2++, Idx, InsertPt); 772 } 773 774 // Anything that used the arg should now use the alloca. 775 I->replaceAllUsesWith(TheAlloca); 776 TheAlloca->takeName(I); 777 AA.replaceWithNewValue(I, TheAlloca); 778 continue; 779 } 780 781 if (I->use_empty()) { 782 AA.deleteValue(I); 783 continue; 784 } 785 786 // Otherwise, if we promoted this argument, then all users are load 787 // instructions (or GEPs with only load users), and all loads should be 788 // using the new argument that we added. 789 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 790 791 while (!I->use_empty()) { 792 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 793 assert(ArgIndices.begin()->empty() && 794 "Load element should sort to front!"); 795 I2->setName(I->getName()+".val"); 796 LI->replaceAllUsesWith(I2); 797 AA.replaceWithNewValue(LI, I2); 798 LI->eraseFromParent(); 799 DEBUG(errs() << "*** Promoted load of argument '" << I->getName() 800 << "' in function '" << F->getName() << "'\n"); 801 } else { 802 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 803 IndicesVector Operands; 804 Operands.reserve(GEP->getNumIndices()); 805 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 806 II != IE; ++II) 807 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); 808 809 // GEPs with a single 0 index can be merged with direct loads 810 if (Operands.size() == 1 && Operands.front() == 0) 811 Operands.clear(); 812 813 Function::arg_iterator TheArg = I2; 814 for (ScalarizeTable::iterator It = ArgIndices.begin(); 815 *It != Operands; ++It, ++TheArg) { 816 assert(It != ArgIndices.end() && "GEP not handled??"); 817 } 818 819 std::string NewName = I->getName(); 820 for (unsigned i = 0, e = Operands.size(); i != e; ++i) { 821 NewName += "." + utostr(Operands[i]); 822 } 823 NewName += ".val"; 824 TheArg->setName(NewName); 825 826 DEBUG(errs() << "*** Promoted agg argument '" << TheArg->getName() 827 << "' of function '" << NF->getName() << "'\n"); 828 829 // All of the uses must be load instructions. Replace them all with 830 // the argument specified by ArgNo. 831 while (!GEP->use_empty()) { 832 LoadInst *L = cast<LoadInst>(GEP->use_back()); 833 L->replaceAllUsesWith(TheArg); 834 AA.replaceWithNewValue(L, TheArg); 835 L->eraseFromParent(); 836 } 837 AA.deleteValue(GEP); 838 GEP->eraseFromParent(); 839 } 840 } 841 842 // Increment I2 past all of the arguments added for this promoted pointer. 843 for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i) 844 ++I2; 845 } 846 847 // Notify the alias analysis implementation that we inserted a new argument. 848 if (ExtraArgHack) 849 AA.copyValue(Context.getNullValue(Type::Int32Ty), NF->arg_begin()); 850 851 852 // Tell the alias analysis that the old function is about to disappear. 853 AA.replaceWithNewValue(F, NF); 854 855 // Now that the old function is dead, delete it. 856 F->eraseFromParent(); 857 return NF; 858} 859