ArgumentPromotion.cpp revision 5ededf7d42417379d230c92fc73912ebb650ede9
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(std::vector<CallGraphNode *> &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; 87static RegisterPass<ArgPromotion> 88X("argpromotion", "Promote 'by reference' arguments to scalars"); 89 90Pass *llvm::createArgumentPromotionPass(unsigned maxElements) { 91 return new ArgPromotion(maxElements); 92} 93 94bool ArgPromotion::runOnSCC(std::vector<CallGraphNode *> &SCC) { 95 bool Changed = false, LocalChange; 96 97 do { // Iterate until we stop promoting from this SCC. 98 LocalChange = false; 99 // Attempt to promote arguments from all functions in this SCC. 100 for (unsigned i = 0, e = SCC.size(); i != e; ++i) 101 if (CallGraphNode *CGN = PromoteArguments(SCC[i])) { 102 LocalChange = true; 103 SCC[i] = CGN; 104 } 105 Changed |= LocalChange; // Remember that we changed something. 106 } while (LocalChange); 107 108 return Changed; 109} 110 111/// PromoteArguments - This method checks the specified function to see if there 112/// are any promotable arguments and if it is safe to promote the function (for 113/// example, all callers are direct). If safe to promote some arguments, it 114/// calls the DoPromotion method. 115/// 116CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) { 117 Function *F = CGN->getFunction(); 118 119 // Make sure that it is local to this module. 120 if (!F || !F->hasLocalLinkage()) return 0; 121 122 // First check: see if there are any pointer arguments! If not, quick exit. 123 SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs; 124 unsigned ArgNo = 0; 125 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 126 I != E; ++I, ++ArgNo) 127 if (isa<PointerType>(I->getType())) 128 PointerArgs.push_back(std::pair<Argument*, unsigned>(I, ArgNo)); 129 if (PointerArgs.empty()) return 0; 130 131 // Second check: make sure that all callers are direct callers. We can't 132 // transform functions that have indirect callers. 133 if (F->hasAddressTaken()) 134 return 0; 135 136 // Check to see which arguments are promotable. If an argument is promotable, 137 // add it to ArgsToPromote. 138 SmallPtrSet<Argument*, 8> ArgsToPromote; 139 SmallPtrSet<Argument*, 8> ByValArgsToTransform; 140 for (unsigned i = 0; i != PointerArgs.size(); ++i) { 141 bool isByVal = F->paramHasAttr(PointerArgs[i].second+1, Attribute::ByVal); 142 143 // If this is a byval argument, and if the aggregate type is small, just 144 // pass the elements, which is always safe. 145 Argument *PtrArg = PointerArgs[i].first; 146 if (isByVal) { 147 const Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType(); 148 if (const StructType *STy = dyn_cast<StructType>(AgTy)) { 149 if (maxElements > 0 && STy->getNumElements() > maxElements) { 150 DEBUG(dbgs() << "argpromotion disable promoting argument '" 151 << PtrArg->getName() << "' because it would require adding more" 152 << " than " << maxElements << " arguments to the function.\n"); 153 } else { 154 // If all the elements are single-value types, we can promote it. 155 bool AllSimple = true; 156 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 157 if (!STy->getElementType(i)->isSingleValueType()) { 158 AllSimple = false; 159 break; 160 } 161 162 // Safe to transform, don't even bother trying to "promote" it. 163 // Passing the elements as a scalar will allow scalarrepl to hack on 164 // the new alloca we introduce. 165 if (AllSimple) { 166 ByValArgsToTransform.insert(PtrArg); 167 continue; 168 } 169 } 170 } 171 } 172 173 // Otherwise, see if we can promote the pointer to its value. 174 if (isSafeToPromoteArgument(PtrArg, isByVal)) 175 ArgsToPromote.insert(PtrArg); 176 } 177 178 // No promotable pointer arguments. 179 if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) 180 return 0; 181 182 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform); 183} 184 185/// IsAlwaysValidPointer - Return true if the specified pointer is always legal 186/// to load. 187static bool IsAlwaysValidPointer(Value *V) { 188 if (isa<AllocaInst>(V) || isa<GlobalVariable>(V)) return true; 189 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) 190 return IsAlwaysValidPointer(GEP->getOperand(0)); 191 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) 192 if (CE->getOpcode() == Instruction::GetElementPtr) 193 return IsAlwaysValidPointer(CE->getOperand(0)); 194 195 return false; 196} 197 198/// AllCalleesPassInValidPointerForArgument - Return true if we can prove that 199/// all callees pass in a valid pointer for the specified function argument. 200static bool AllCalleesPassInValidPointerForArgument(Argument *Arg) { 201 Function *Callee = Arg->getParent(); 202 203 unsigned ArgNo = std::distance(Callee->arg_begin(), 204 Function::arg_iterator(Arg)); 205 206 // Look at all call sites of the function. At this pointer we know we only 207 // have direct callees. 208 for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end(); 209 UI != E; ++UI) { 210 CallSite CS = CallSite::get(*UI); 211 assert(CS.getInstruction() && "Should only have direct calls!"); 212 213 if (!IsAlwaysValidPointer(CS.getArgument(ArgNo))) 214 return false; 215 } 216 return true; 217} 218 219/// Returns true if Prefix is a prefix of longer. That means, Longer has a size 220/// that is greater than or equal to the size of prefix, and each of the 221/// elements in Prefix is the same as the corresponding elements in Longer. 222/// 223/// This means it also returns true when Prefix and Longer are equal! 224static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix, 225 const ArgPromotion::IndicesVector &Longer) { 226 if (Prefix.size() > Longer.size()) 227 return false; 228 for (unsigned i = 0, e = Prefix.size(); i != e; ++i) 229 if (Prefix[i] != Longer[i]) 230 return false; 231 return true; 232} 233 234 235/// Checks if Indices, or a prefix of Indices, is in Set. 236static bool PrefixIn(const ArgPromotion::IndicesVector &Indices, 237 std::set<ArgPromotion::IndicesVector> &Set) { 238 std::set<ArgPromotion::IndicesVector>::iterator Low; 239 Low = Set.upper_bound(Indices); 240 if (Low != Set.begin()) 241 Low--; 242 // Low is now the last element smaller than or equal to Indices. This means 243 // it points to a prefix of Indices (possibly Indices itself), if such 244 // prefix exists. 245 // 246 // This load is safe if any prefix of its operands is safe to load. 247 return Low != Set.end() && IsPrefix(*Low, Indices); 248} 249 250/// Mark the given indices (ToMark) as safe in the the given set of indices 251/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there 252/// is already a prefix of Indices in Safe, Indices are implicitely marked safe 253/// already. Furthermore, any indices that Indices is itself a prefix of, are 254/// removed from Safe (since they are implicitely safe because of Indices now). 255static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark, 256 std::set<ArgPromotion::IndicesVector> &Safe) { 257 std::set<ArgPromotion::IndicesVector>::iterator Low; 258 Low = Safe.upper_bound(ToMark); 259 // Guard against the case where Safe is empty 260 if (Low != Safe.begin()) 261 Low--; 262 // Low is now the last element smaller than or equal to Indices. This 263 // means it points to a prefix of Indices (possibly Indices itself), if 264 // such prefix exists. 265 if (Low != Safe.end()) { 266 if (IsPrefix(*Low, ToMark)) 267 // If there is already a prefix of these indices (or exactly these 268 // indices) marked a safe, don't bother adding these indices 269 return; 270 271 // Increment Low, so we can use it as a "insert before" hint 272 ++Low; 273 } 274 // Insert 275 Low = Safe.insert(Low, ToMark); 276 ++Low; 277 // If there we're a prefix of longer index list(s), remove those 278 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end(); 279 while (Low != End && IsPrefix(ToMark, *Low)) { 280 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low; 281 ++Low; 282 Safe.erase(Remove); 283 } 284} 285 286/// isSafeToPromoteArgument - As you might guess from the name of this method, 287/// it checks to see if it is both safe and useful to promote the argument. 288/// This method limits promotion of aggregates to only promote up to three 289/// elements of the aggregate in order to avoid exploding the number of 290/// arguments passed in. 291bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { 292 typedef std::set<IndicesVector> GEPIndicesSet; 293 294 // Quick exit for unused arguments 295 if (Arg->use_empty()) 296 return true; 297 298 // We can only promote this argument if all of the uses are loads, or are GEP 299 // instructions (with constant indices) that are subsequently loaded. 300 // 301 // Promoting the argument causes it to be loaded in the caller 302 // unconditionally. This is only safe if we can prove that either the load 303 // would have happened in the callee anyway (ie, there is a load in the entry 304 // block) or the pointer passed in at every call site is guaranteed to be 305 // valid. 306 // In the former case, invalid loads can happen, but would have happened 307 // anyway, in the latter case, invalid loads won't happen. This prevents us 308 // from introducing an invalid load that wouldn't have happened in the 309 // original code. 310 // 311 // This set will contain all sets of indices that are loaded in the entry 312 // block, and thus are safe to unconditionally load in the caller. 313 GEPIndicesSet SafeToUnconditionallyLoad; 314 315 // This set contains all the sets of indices that we are planning to promote. 316 // This makes it possible to limit the number of arguments added. 317 GEPIndicesSet ToPromote; 318 319 // If the pointer is always valid, any load with first index 0 is valid. 320 if(isByVal || AllCalleesPassInValidPointerForArgument(Arg)) 321 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); 322 323 // First, iterate the entry block and mark loads of (geps of) arguments as 324 // safe. 325 BasicBlock *EntryBlock = Arg->getParent()->begin(); 326 // Declare this here so we can reuse it 327 IndicesVector Indices; 328 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end(); 329 I != E; ++I) 330 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 331 Value *V = LI->getPointerOperand(); 332 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { 333 V = GEP->getPointerOperand(); 334 if (V == Arg) { 335 // This load actually loads (part of) Arg? Check the indices then. 336 Indices.reserve(GEP->getNumIndices()); 337 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 338 II != IE; ++II) 339 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) 340 Indices.push_back(CI->getSExtValue()); 341 else 342 // We found a non-constant GEP index for this argument? Bail out 343 // right away, can't promote this argument at all. 344 return false; 345 346 // Indices checked out, mark them as safe 347 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); 348 Indices.clear(); 349 } 350 } else if (V == Arg) { 351 // Direct loads are equivalent to a GEP with a single 0 index. 352 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); 353 } 354 } 355 356 // Now, iterate all uses of the argument to see if there are any uses that are 357 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. 358 SmallVector<LoadInst*, 16> Loads; 359 IndicesVector Operands; 360 for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); 361 UI != E; ++UI) { 362 Operands.clear(); 363 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 364 if (LI->isVolatile()) return false; // Don't hack volatile loads 365 Loads.push_back(LI); 366 // Direct loads are equivalent to a GEP with a zero index and then a load. 367 Operands.push_back(0); 368 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) { 369 if (GEP->use_empty()) { 370 // Dead GEP's cause trouble later. Just remove them if we run into 371 // them. 372 getAnalysis<AliasAnalysis>().deleteValue(GEP); 373 GEP->eraseFromParent(); 374 // TODO: This runs the above loop over and over again for dead GEPS 375 // Couldn't we just do increment the UI iterator earlier and erase the 376 // use? 377 return isSafeToPromoteArgument(Arg, isByVal); 378 } 379 380 // Ensure that all of the indices are constants. 381 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); 382 i != e; ++i) 383 if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) 384 Operands.push_back(C->getSExtValue()); 385 else 386 return false; // Not a constant operand GEP! 387 388 // Ensure that the only users of the GEP are load instructions. 389 for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); 390 UI != E; ++UI) 391 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 392 if (LI->isVolatile()) return false; // Don't hack volatile loads 393 Loads.push_back(LI); 394 } else { 395 // Other uses than load? 396 return false; 397 } 398 } else { 399 return false; // Not a load or a GEP. 400 } 401 402 // Now, see if it is safe to promote this load / loads of this GEP. Loading 403 // is safe if Operands, or a prefix of Operands, is marked as safe. 404 if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) 405 return false; 406 407 // See if we are already promoting a load with these indices. If not, check 408 // to make sure that we aren't promoting too many elements. If so, nothing 409 // to do. 410 if (ToPromote.find(Operands) == ToPromote.end()) { 411 if (maxElements > 0 && ToPromote.size() == maxElements) { 412 DEBUG(dbgs() << "argpromotion not promoting argument '" 413 << Arg->getName() << "' because it would require adding more " 414 << "than " << maxElements << " arguments to the function.\n"); 415 // We limit aggregate promotion to only promoting up to a fixed number 416 // of elements of the aggregate. 417 return false; 418 } 419 ToPromote.insert(Operands); 420 } 421 } 422 423 if (Loads.empty()) return true; // No users, this is a dead argument. 424 425 // Okay, now we know that the argument is only used by load instructions and 426 // it is safe to unconditionally perform all of them. Use alias analysis to 427 // check to see if the pointer is guaranteed to not be modified from entry of 428 // the function to each of the load instructions. 429 430 // Because there could be several/many load instructions, remember which 431 // blocks we know to be transparent to the load. 432 SmallPtrSet<BasicBlock*, 16> TranspBlocks; 433 434 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 435 TargetData *TD = getAnalysisIfAvailable<TargetData>(); 436 if (!TD) return false; // Without TargetData, assume the worst. 437 438 for (unsigned i = 0, e = Loads.size(); i != e; ++i) { 439 // Check to see if the load is invalidated from the start of the block to 440 // the load itself. 441 LoadInst *Load = Loads[i]; 442 BasicBlock *BB = Load->getParent(); 443 444 const PointerType *LoadTy = 445 cast<PointerType>(Load->getPointerOperand()->getType()); 446 unsigned LoadSize =(unsigned)TD->getTypeStoreSize(LoadTy->getElementType()); 447 448 if (AA.canInstructionRangeModify(BB->front(), *Load, Arg, LoadSize)) 449 return false; // Pointer is invalidated! 450 451 // Now check every path from the entry block to the load for transparency. 452 // To do this, we perform a depth first search on the inverse CFG from the 453 // loading block. 454 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) 455 for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> > 456 I = idf_ext_begin(*PI, TranspBlocks), 457 E = idf_ext_end(*PI, TranspBlocks); I != E; ++I) 458 if (AA.canBasicBlockModify(**I, Arg, LoadSize)) 459 return false; 460 } 461 462 // If the path from the entry of the function to each load is free of 463 // instructions that potentially invalidate the load, we can make the 464 // transformation! 465 return true; 466} 467 468/// DoPromotion - This method actually performs the promotion of the specified 469/// arguments, and returns the new function. At this point, we know that it's 470/// safe to do so. 471CallGraphNode *ArgPromotion::DoPromotion(Function *F, 472 SmallPtrSet<Argument*, 8> &ArgsToPromote, 473 SmallPtrSet<Argument*, 8> &ByValArgsToTransform) { 474 475 // Start by computing a new prototype for the function, which is the same as 476 // the old function, but has modified arguments. 477 const FunctionType *FTy = F->getFunctionType(); 478 std::vector<const Type*> Params; 479 480 typedef std::set<IndicesVector> ScalarizeTable; 481 482 // ScalarizedElements - If we are promoting a pointer that has elements 483 // accessed out of it, keep track of which elements are accessed so that we 484 // can add one argument for each. 485 // 486 // Arguments that are directly loaded will have a zero element value here, to 487 // handle cases where there are both a direct load and GEP accesses. 488 // 489 std::map<Argument*, ScalarizeTable> ScalarizedElements; 490 491 // OriginalLoads - Keep track of a representative load instruction from the 492 // original function so that we can tell the alias analysis implementation 493 // what the new GEP/Load instructions we are inserting look like. 494 std::map<IndicesVector, LoadInst*> OriginalLoads; 495 496 // Attributes - Keep track of the parameter attributes for the arguments 497 // that we are *not* promoting. For the ones that we do promote, the parameter 498 // attributes are lost 499 SmallVector<AttributeWithIndex, 8> AttributesVec; 500 const AttrListPtr &PAL = F->getAttributes(); 501 502 // Add any return attributes. 503 if (Attributes attrs = PAL.getRetAttributes()) 504 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 505 506 // First, determine the new argument list 507 unsigned ArgIndex = 1; 508 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; 509 ++I, ++ArgIndex) { 510 if (ByValArgsToTransform.count(I)) { 511 // Simple byval argument? Just add all the struct element types. 512 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 513 const StructType *STy = cast<StructType>(AgTy); 514 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 515 Params.push_back(STy->getElementType(i)); 516 ++NumByValArgsPromoted; 517 } else if (!ArgsToPromote.count(I)) { 518 // Unchanged argument 519 Params.push_back(I->getType()); 520 if (Attributes attrs = PAL.getParamAttributes(ArgIndex)) 521 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), attrs)); 522 } else if (I->use_empty()) { 523 // Dead argument (which are always marked as promotable) 524 ++NumArgumentsDead; 525 } else { 526 // Okay, this is being promoted. This means that the only uses are loads 527 // or GEPs which are only used by loads 528 529 // In this table, we will track which indices are loaded from the argument 530 // (where direct loads are tracked as no indices). 531 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 532 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; 533 ++UI) { 534 Instruction *User = cast<Instruction>(*UI); 535 assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User)); 536 IndicesVector Indices; 537 Indices.reserve(User->getNumOperands() - 1); 538 // Since loads will only have a single operand, and GEPs only a single 539 // non-index operand, this will record direct loads without any indices, 540 // and gep+loads with the GEP indices. 541 for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end(); 542 II != IE; ++II) 543 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue()); 544 // GEPs with a single 0 index can be merged with direct loads 545 if (Indices.size() == 1 && Indices.front() == 0) 546 Indices.clear(); 547 ArgIndices.insert(Indices); 548 LoadInst *OrigLoad; 549 if (LoadInst *L = dyn_cast<LoadInst>(User)) 550 OrigLoad = L; 551 else 552 // Take any load, we will use it only to update Alias Analysis 553 OrigLoad = cast<LoadInst>(User->use_back()); 554 OriginalLoads[Indices] = OrigLoad; 555 } 556 557 // Add a parameter to the function for each element passed in. 558 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 559 E = ArgIndices.end(); SI != E; ++SI) { 560 // not allowed to dereference ->begin() if size() is 0 561 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), 562 SI->begin(), 563 SI->end())); 564 assert(Params.back()); 565 } 566 567 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty()) 568 ++NumArgumentsPromoted; 569 else 570 ++NumAggregatesPromoted; 571 } 572 } 573 574 // Add any function attributes. 575 if (Attributes attrs = PAL.getFnAttributes()) 576 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 577 578 const Type *RetTy = FTy->getReturnType(); 579 580 // Work around LLVM bug PR56: the CWriter cannot emit varargs functions which 581 // have zero fixed arguments. 582 bool ExtraArgHack = false; 583 if (Params.empty() && FTy->isVarArg()) { 584 ExtraArgHack = true; 585 Params.push_back(Type::getInt32Ty(F->getContext())); 586 } 587 588 // Construct the new function type using the new arguments. 589 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); 590 591 // Create the new function body and insert it into the module. 592 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); 593 NF->copyAttributesFrom(F); 594 595 596 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n" 597 << "From: " << *F); 598 599 // Recompute the parameter attributes list based on the new arguments for 600 // the function. 601 NF->setAttributes(AttrListPtr::get(AttributesVec.begin(), 602 AttributesVec.end())); 603 AttributesVec.clear(); 604 605 F->getParent()->getFunctionList().insert(F, NF); 606 NF->takeName(F); 607 608 // Get the alias analysis information that we need to update to reflect our 609 // changes. 610 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 611 612 // Get the callgraph information that we need to update to reflect our 613 // changes. 614 CallGraph &CG = getAnalysis<CallGraph>(); 615 616 // Get a new callgraph node for NF. 617 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF); 618 619 620 // Loop over all of the callers of the function, transforming the call sites 621 // to pass in the loaded pointers. 622 // 623 SmallVector<Value*, 16> Args; 624 while (!F->use_empty()) { 625 CallSite CS = CallSite::get(F->use_back()); 626 Instruction *Call = CS.getInstruction(); 627 const AttrListPtr &CallPAL = CS.getAttributes(); 628 629 // Add any return attributes. 630 if (Attributes attrs = CallPAL.getRetAttributes()) 631 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 632 633 // Loop over the operands, inserting GEP and loads in the caller as 634 // appropriate. 635 CallSite::arg_iterator AI = CS.arg_begin(); 636 ArgIndex = 1; 637 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 638 I != E; ++I, ++AI, ++ArgIndex) 639 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 640 Args.push_back(*AI); // Unmodified argument 641 642 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 643 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 644 645 } else if (ByValArgsToTransform.count(I)) { 646 // Emit a GEP and load for each element of the struct. 647 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 648 const StructType *STy = cast<StructType>(AgTy); 649 Value *Idxs[2] = { 650 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 651 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 652 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 653 Value *Idx = GetElementPtrInst::Create(*AI, Idxs, Idxs+2, 654 (*AI)->getName()+"."+utostr(i), 655 Call); 656 // TODO: Tell AA about the new values? 657 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); 658 } 659 } else if (!I->use_empty()) { 660 // Non-dead argument: insert GEPs and loads as appropriate. 661 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 662 // Store the Value* version of the indices in here, but declare it now 663 // for reuse 664 std::vector<Value*> Ops; 665 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 666 E = ArgIndices.end(); SI != E; ++SI) { 667 Value *V = *AI; 668 LoadInst *OrigLoad = OriginalLoads[*SI]; 669 if (!SI->empty()) { 670 Ops.reserve(SI->size()); 671 const Type *ElTy = V->getType(); 672 for (IndicesVector::const_iterator II = SI->begin(), 673 IE = SI->end(); II != IE; ++II) { 674 // Use i32 to index structs, and i64 for others (pointers/arrays). 675 // This satisfies GEP constraints. 676 const Type *IdxTy = (isa<StructType>(ElTy) ? 677 Type::getInt32Ty(F->getContext()) : 678 Type::getInt64Ty(F->getContext())); 679 Ops.push_back(ConstantInt::get(IdxTy, *II)); 680 // Keep track of the type we're currently indexing 681 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II); 682 } 683 // And create a GEP to extract those indices 684 V = GetElementPtrInst::Create(V, Ops.begin(), Ops.end(), 685 V->getName()+".idx", Call); 686 Ops.clear(); 687 AA.copyValue(OrigLoad->getOperand(0), V); 688 } 689 Args.push_back(new LoadInst(V, V->getName()+".val", Call)); 690 AA.copyValue(OrigLoad, Args.back()); 691 } 692 } 693 694 if (ExtraArgHack) 695 Args.push_back(Constant::getNullValue(Type::getInt32Ty(F->getContext()))); 696 697 // Push any varargs arguments on the list 698 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { 699 Args.push_back(*AI); 700 if (Attributes Attrs = CallPAL.getParamAttributes(ArgIndex)) 701 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 702 } 703 704 // Add any function attributes. 705 if (Attributes attrs = CallPAL.getFnAttributes()) 706 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 707 708 Instruction *New; 709 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 710 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 711 Args.begin(), Args.end(), "", Call); 712 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 713 cast<InvokeInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 714 AttributesVec.end())); 715 } else { 716 New = CallInst::Create(NF, Args.begin(), Args.end(), "", Call); 717 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 718 cast<CallInst>(New)->setAttributes(AttrListPtr::get(AttributesVec.begin(), 719 AttributesVec.end())); 720 if (cast<CallInst>(Call)->isTailCall()) 721 cast<CallInst>(New)->setTailCall(); 722 } 723 Args.clear(); 724 AttributesVec.clear(); 725 726 // Update the alias analysis implementation to know that we are replacing 727 // the old call with a new one. 728 AA.replaceWithNewValue(Call, New); 729 730 // Update the callgraph to know that the callsite has been transformed. 731 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()]; 732 CalleeNode->replaceCallEdge(Call, New, NF_CGN); 733 734 if (!Call->use_empty()) { 735 Call->replaceAllUsesWith(New); 736 New->takeName(Call); 737 } 738 739 // Finally, remove the old call from the program, reducing the use-count of 740 // F. 741 Call->eraseFromParent(); 742 } 743 744 // Since we have now created the new function, splice the body of the old 745 // function right into the new function, leaving the old rotting hulk of the 746 // function empty. 747 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 748 749 // Loop over the argument list, transfering uses of the old arguments over to 750 // the new arguments, also transfering over the names as well. 751 // 752 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 753 I2 = NF->arg_begin(); I != E; ++I) { 754 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 755 // If this is an unmodified argument, move the name and users over to the 756 // new version. 757 I->replaceAllUsesWith(I2); 758 I2->takeName(I); 759 AA.replaceWithNewValue(I, I2); 760 ++I2; 761 continue; 762 } 763 764 if (ByValArgsToTransform.count(I)) { 765 // In the callee, we create an alloca, and store each of the new incoming 766 // arguments into the alloca. 767 Instruction *InsertPt = NF->begin()->begin(); 768 769 // Just add all the struct element types. 770 const Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 771 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 772 const StructType *STy = cast<StructType>(AgTy); 773 Value *Idxs[2] = { 774 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 775 776 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 777 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 778 Value *Idx = 779 GetElementPtrInst::Create(TheAlloca, Idxs, Idxs+2, 780 TheAlloca->getName()+"."+Twine(i), 781 InsertPt); 782 I2->setName(I->getName()+"."+Twine(i)); 783 new StoreInst(I2++, Idx, InsertPt); 784 } 785 786 // Anything that used the arg should now use the alloca. 787 I->replaceAllUsesWith(TheAlloca); 788 TheAlloca->takeName(I); 789 AA.replaceWithNewValue(I, TheAlloca); 790 continue; 791 } 792 793 if (I->use_empty()) { 794 AA.deleteValue(I); 795 continue; 796 } 797 798 // Otherwise, if we promoted this argument, then all users are load 799 // instructions (or GEPs with only load users), and all loads should be 800 // using the new argument that we added. 801 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 802 803 while (!I->use_empty()) { 804 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 805 assert(ArgIndices.begin()->empty() && 806 "Load element should sort to front!"); 807 I2->setName(I->getName()+".val"); 808 LI->replaceAllUsesWith(I2); 809 AA.replaceWithNewValue(LI, I2); 810 LI->eraseFromParent(); 811 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName() 812 << "' in function '" << F->getName() << "'\n"); 813 } else { 814 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 815 IndicesVector Operands; 816 Operands.reserve(GEP->getNumIndices()); 817 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 818 II != IE; ++II) 819 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); 820 821 // GEPs with a single 0 index can be merged with direct loads 822 if (Operands.size() == 1 && Operands.front() == 0) 823 Operands.clear(); 824 825 Function::arg_iterator TheArg = I2; 826 for (ScalarizeTable::iterator It = ArgIndices.begin(); 827 *It != Operands; ++It, ++TheArg) { 828 assert(It != ArgIndices.end() && "GEP not handled??"); 829 } 830 831 std::string NewName = I->getName(); 832 for (unsigned i = 0, e = Operands.size(); i != e; ++i) { 833 NewName += "." + utostr(Operands[i]); 834 } 835 NewName += ".val"; 836 TheArg->setName(NewName); 837 838 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName() 839 << "' of function '" << NF->getName() << "'\n"); 840 841 // All of the uses must be load instructions. Replace them all with 842 // the argument specified by ArgNo. 843 while (!GEP->use_empty()) { 844 LoadInst *L = cast<LoadInst>(GEP->use_back()); 845 L->replaceAllUsesWith(TheArg); 846 AA.replaceWithNewValue(L, TheArg); 847 L->eraseFromParent(); 848 } 849 AA.deleteValue(GEP); 850 GEP->eraseFromParent(); 851 } 852 } 853 854 // Increment I2 past all of the arguments added for this promoted pointer. 855 for (unsigned i = 0, e = ArgIndices.size(); i != e; ++i) 856 ++I2; 857 } 858 859 // Notify the alias analysis implementation that we inserted a new argument. 860 if (ExtraArgHack) 861 AA.copyValue(Constant::getNullValue(Type::getInt32Ty(F->getContext())), 862 NF->arg_begin()); 863 864 865 // Tell the alias analysis that the old function is about to disappear. 866 AA.replaceWithNewValue(F, NF); 867 868 869 NF_CGN->stealCalledFunctionsFrom(CG[F]); 870 871 // Now that the old function is dead, delete it. 872 delete CG.removeFunctionFromModule(F); 873 874 return NF_CGN; 875} 876