ArgumentPromotion.cpp revision 7be7848e17f60825f5fbc177b8a25909a30ddb00
1//===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This pass promotes "by reference" arguments to be "by value" arguments. In 11// practice, this means looking for internal functions that have pointer 12// arguments. If it can prove, through the use of alias analysis, that an 13// argument is *only* loaded, then it can pass the value into the function 14// instead of the address of the value. This can cause recursive simplification 15// of code and lead to the elimination of allocas (especially in C++ template 16// code like the STL). 17// 18// This pass also handles aggregate arguments that are passed into a function, 19// scalarizing them if the elements of the aggregate are only loaded. Note that 20// by default it refuses to scalarize aggregates which would require passing in 21// more than three operands to the function, because passing thousands of 22// operands for a large array or structure is unprofitable! This limit can be 23// configured or disabled, however. 24// 25// Note that this transformation could also be done for arguments that are only 26// stored to (returning the value instead), but does not currently. This case 27// would be best handled when and if LLVM begins supporting multiple return 28// values from functions. 29// 30//===----------------------------------------------------------------------===// 31 32#define DEBUG_TYPE "argpromotion" 33#include "llvm/Transforms/IPO.h" 34#include "llvm/Constants.h" 35#include "llvm/DerivedTypes.h" 36#include "llvm/Module.h" 37#include "llvm/CallGraphSCCPass.h" 38#include "llvm/Instructions.h" 39#include "llvm/LLVMContext.h" 40#include "llvm/Analysis/AliasAnalysis.h" 41#include "llvm/Analysis/CallGraph.h" 42#include "llvm/Support/CallSite.h" 43#include "llvm/Support/CFG.h" 44#include "llvm/Support/Debug.h" 45#include "llvm/Support/raw_ostream.h" 46#include "llvm/ADT/DepthFirstIterator.h" 47#include "llvm/ADT/Statistic.h" 48#include "llvm/ADT/StringExtras.h" 49#include <set> 50using namespace llvm; 51 52STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted"); 53STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted"); 54STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted"); 55STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated"); 56 57namespace { 58 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass. 59 /// 60 struct ArgPromotion : public CallGraphSCCPass { 61 virtual void getAnalysisUsage(AnalysisUsage &AU) const { 62 AU.addRequired<AliasAnalysis>(); 63 CallGraphSCCPass::getAnalysisUsage(AU); 64 } 65 66 virtual bool runOnSCC(CallGraphSCC &SCC); 67 static char ID; // Pass identification, replacement for typeid 68 explicit ArgPromotion(unsigned maxElements = 3) 69 : CallGraphSCCPass(ID), maxElements(maxElements) { 70 initializeArgPromotionPass(*PassRegistry::getPassRegistry()); 71 } 72 73 /// A vector used to hold the indices of a single GEP instruction 74 typedef std::vector<uint64_t> IndicesVector; 75 76 private: 77 CallGraphNode *PromoteArguments(CallGraphNode *CGN); 78 bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const; 79 CallGraphNode *DoPromotion(Function *F, 80 SmallPtrSet<Argument*, 8> &ArgsToPromote, 81 SmallPtrSet<Argument*, 8> &ByValArgsToTransform); 82 /// The maximum number of elements to expand, or 0 for unlimited. 83 unsigned maxElements; 84 }; 85} 86 87char ArgPromotion::ID = 0; 88INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion", 89 "Promote 'by reference' arguments to scalars", false, false) 90INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 91INITIALIZE_AG_DEPENDENCY(CallGraph) 92INITIALIZE_PASS_END(ArgPromotion, "argpromotion", 93 "Promote 'by reference' arguments to scalars", false, false) 94 95Pass *llvm::createArgumentPromotionPass(unsigned maxElements) { 96 return new ArgPromotion(maxElements); 97} 98 99bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) { 100 bool Changed = false, LocalChange; 101 102 do { // Iterate until we stop promoting from this SCC. 103 LocalChange = false; 104 // Attempt to promote arguments from all functions in this SCC. 105 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) { 106 if (CallGraphNode *CGN = PromoteArguments(*I)) { 107 LocalChange = true; 108 SCC.ReplaceNode(*I, CGN); 109 } 110 } 111 Changed |= LocalChange; // Remember that we changed something. 112 } while (LocalChange); 113 114 return Changed; 115} 116 117/// PromoteArguments - This method checks the specified function to see if there 118/// are any promotable arguments and if it is safe to promote the function (for 119/// example, all callers are direct). If safe to promote some arguments, it 120/// calls the DoPromotion method. 121/// 122CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) { 123 Function *F = CGN->getFunction(); 124 125 // Make sure that it is local to this module. 126 if (!F || !F->hasLocalLinkage()) return 0; 127 128 // First check: see if there are any pointer arguments! If not, quick exit. 129 SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs; 130 unsigned ArgNo = 0; 131 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 132 I != E; ++I, ++ArgNo) 133 if (I->getType()->isPointerTy()) 134 PointerArgs.push_back(std::pair<Argument*, unsigned>(I, ArgNo)); 135 if (PointerArgs.empty()) return 0; 136 137 // Second check: make sure that all callers are direct callers. We can't 138 // transform functions that have indirect callers. Also see if the function 139 // is self-recursive. 140 bool isSelfRecursive = false; 141 for (Value::use_iterator UI = F->use_begin(), E = F->use_end(); 142 UI != E; ++UI) { 143 CallSite CS(*UI); 144 // Must be a direct call. 145 if (CS.getInstruction() == 0 || !CS.isCallee(UI)) return 0; 146 147 if (CS.getInstruction()->getParent()->getParent() == F) 148 isSelfRecursive = true; 149 } 150 151 // Check to see which arguments are promotable. If an argument is promotable, 152 // add it to ArgsToPromote. 153 SmallPtrSet<Argument*, 8> ArgsToPromote; 154 SmallPtrSet<Argument*, 8> ByValArgsToTransform; 155 for (unsigned i = 0; i != PointerArgs.size(); ++i) { 156 bool isByVal=F->getParamAttributes(PointerArgs[i].second+1). 157 hasAttribute(Attributes::ByVal); 158 Argument *PtrArg = PointerArgs[i].first; 159 Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType(); 160 161 // If this is a byval argument, and if the aggregate type is small, just 162 // pass the elements, which is always safe. 163 if (isByVal) { 164 if (StructType *STy = dyn_cast<StructType>(AgTy)) { 165 if (maxElements > 0 && STy->getNumElements() > maxElements) { 166 DEBUG(dbgs() << "argpromotion disable promoting argument '" 167 << PtrArg->getName() << "' because it would require adding more" 168 << " than " << maxElements << " arguments to the function.\n"); 169 continue; 170 } 171 172 // If all the elements are single-value types, we can promote it. 173 bool AllSimple = true; 174 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 175 if (!STy->getElementType(i)->isSingleValueType()) { 176 AllSimple = false; 177 break; 178 } 179 } 180 181 // Safe to transform, don't even bother trying to "promote" it. 182 // Passing the elements as a scalar will allow scalarrepl to hack on 183 // the new alloca we introduce. 184 if (AllSimple) { 185 ByValArgsToTransform.insert(PtrArg); 186 continue; 187 } 188 } 189 } 190 191 // If the argument is a recursive type and we're in a recursive 192 // function, we could end up infinitely peeling the function argument. 193 if (isSelfRecursive) { 194 if (StructType *STy = dyn_cast<StructType>(AgTy)) { 195 bool RecursiveType = false; 196 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 197 if (STy->getElementType(i) == PtrArg->getType()) { 198 RecursiveType = true; 199 break; 200 } 201 } 202 if (RecursiveType) 203 continue; 204 } 205 } 206 207 // Otherwise, see if we can promote the pointer to its value. 208 if (isSafeToPromoteArgument(PtrArg, isByVal)) 209 ArgsToPromote.insert(PtrArg); 210 } 211 212 // No promotable pointer arguments. 213 if (ArgsToPromote.empty() && ByValArgsToTransform.empty()) 214 return 0; 215 216 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform); 217} 218 219/// AllCallersPassInValidPointerForArgument - Return true if we can prove that 220/// all callees pass in a valid pointer for the specified function argument. 221static bool AllCallersPassInValidPointerForArgument(Argument *Arg) { 222 Function *Callee = Arg->getParent(); 223 224 unsigned ArgNo = std::distance(Callee->arg_begin(), 225 Function::arg_iterator(Arg)); 226 227 // Look at all call sites of the function. At this pointer we know we only 228 // have direct callees. 229 for (Value::use_iterator UI = Callee->use_begin(), E = Callee->use_end(); 230 UI != E; ++UI) { 231 CallSite CS(*UI); 232 assert(CS && "Should only have direct calls!"); 233 234 if (!CS.getArgument(ArgNo)->isDereferenceablePointer()) 235 return false; 236 } 237 return true; 238} 239 240/// Returns true if Prefix is a prefix of longer. That means, Longer has a size 241/// that is greater than or equal to the size of prefix, and each of the 242/// elements in Prefix is the same as the corresponding elements in Longer. 243/// 244/// This means it also returns true when Prefix and Longer are equal! 245static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix, 246 const ArgPromotion::IndicesVector &Longer) { 247 if (Prefix.size() > Longer.size()) 248 return false; 249 return std::equal(Prefix.begin(), Prefix.end(), Longer.begin()); 250} 251 252 253/// Checks if Indices, or a prefix of Indices, is in Set. 254static bool PrefixIn(const ArgPromotion::IndicesVector &Indices, 255 std::set<ArgPromotion::IndicesVector> &Set) { 256 std::set<ArgPromotion::IndicesVector>::iterator Low; 257 Low = Set.upper_bound(Indices); 258 if (Low != Set.begin()) 259 Low--; 260 // Low is now the last element smaller than or equal to Indices. This means 261 // it points to a prefix of Indices (possibly Indices itself), if such 262 // prefix exists. 263 // 264 // This load is safe if any prefix of its operands is safe to load. 265 return Low != Set.end() && IsPrefix(*Low, Indices); 266} 267 268/// Mark the given indices (ToMark) as safe in the given set of indices 269/// (Safe). Marking safe usually means adding ToMark to Safe. However, if there 270/// is already a prefix of Indices in Safe, Indices are implicitely marked safe 271/// already. Furthermore, any indices that Indices is itself a prefix of, are 272/// removed from Safe (since they are implicitely safe because of Indices now). 273static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark, 274 std::set<ArgPromotion::IndicesVector> &Safe) { 275 std::set<ArgPromotion::IndicesVector>::iterator Low; 276 Low = Safe.upper_bound(ToMark); 277 // Guard against the case where Safe is empty 278 if (Low != Safe.begin()) 279 Low--; 280 // Low is now the last element smaller than or equal to Indices. This 281 // means it points to a prefix of Indices (possibly Indices itself), if 282 // such prefix exists. 283 if (Low != Safe.end()) { 284 if (IsPrefix(*Low, ToMark)) 285 // If there is already a prefix of these indices (or exactly these 286 // indices) marked a safe, don't bother adding these indices 287 return; 288 289 // Increment Low, so we can use it as a "insert before" hint 290 ++Low; 291 } 292 // Insert 293 Low = Safe.insert(Low, ToMark); 294 ++Low; 295 // If there we're a prefix of longer index list(s), remove those 296 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end(); 297 while (Low != End && IsPrefix(ToMark, *Low)) { 298 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low; 299 ++Low; 300 Safe.erase(Remove); 301 } 302} 303 304/// isSafeToPromoteArgument - As you might guess from the name of this method, 305/// it checks to see if it is both safe and useful to promote the argument. 306/// This method limits promotion of aggregates to only promote up to three 307/// elements of the aggregate in order to avoid exploding the number of 308/// arguments passed in. 309bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg, bool isByVal) const { 310 typedef std::set<IndicesVector> GEPIndicesSet; 311 312 // Quick exit for unused arguments 313 if (Arg->use_empty()) 314 return true; 315 316 // We can only promote this argument if all of the uses are loads, or are GEP 317 // instructions (with constant indices) that are subsequently loaded. 318 // 319 // Promoting the argument causes it to be loaded in the caller 320 // unconditionally. This is only safe if we can prove that either the load 321 // would have happened in the callee anyway (ie, there is a load in the entry 322 // block) or the pointer passed in at every call site is guaranteed to be 323 // valid. 324 // In the former case, invalid loads can happen, but would have happened 325 // anyway, in the latter case, invalid loads won't happen. This prevents us 326 // from introducing an invalid load that wouldn't have happened in the 327 // original code. 328 // 329 // This set will contain all sets of indices that are loaded in the entry 330 // block, and thus are safe to unconditionally load in the caller. 331 GEPIndicesSet SafeToUnconditionallyLoad; 332 333 // This set contains all the sets of indices that we are planning to promote. 334 // This makes it possible to limit the number of arguments added. 335 GEPIndicesSet ToPromote; 336 337 // If the pointer is always valid, any load with first index 0 is valid. 338 if (isByVal || AllCallersPassInValidPointerForArgument(Arg)) 339 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0)); 340 341 // First, iterate the entry block and mark loads of (geps of) arguments as 342 // safe. 343 BasicBlock *EntryBlock = Arg->getParent()->begin(); 344 // Declare this here so we can reuse it 345 IndicesVector Indices; 346 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end(); 347 I != E; ++I) 348 if (LoadInst *LI = dyn_cast<LoadInst>(I)) { 349 Value *V = LI->getPointerOperand(); 350 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) { 351 V = GEP->getPointerOperand(); 352 if (V == Arg) { 353 // This load actually loads (part of) Arg? Check the indices then. 354 Indices.reserve(GEP->getNumIndices()); 355 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 356 II != IE; ++II) 357 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II)) 358 Indices.push_back(CI->getSExtValue()); 359 else 360 // We found a non-constant GEP index for this argument? Bail out 361 // right away, can't promote this argument at all. 362 return false; 363 364 // Indices checked out, mark them as safe 365 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad); 366 Indices.clear(); 367 } 368 } else if (V == Arg) { 369 // Direct loads are equivalent to a GEP with a single 0 index. 370 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad); 371 } 372 } 373 374 // Now, iterate all uses of the argument to see if there are any uses that are 375 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote. 376 SmallVector<LoadInst*, 16> Loads; 377 IndicesVector Operands; 378 for (Value::use_iterator UI = Arg->use_begin(), E = Arg->use_end(); 379 UI != E; ++UI) { 380 User *U = *UI; 381 Operands.clear(); 382 if (LoadInst *LI = dyn_cast<LoadInst>(U)) { 383 // Don't hack volatile/atomic loads 384 if (!LI->isSimple()) return false; 385 Loads.push_back(LI); 386 // Direct loads are equivalent to a GEP with a zero index and then a load. 387 Operands.push_back(0); 388 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) { 389 if (GEP->use_empty()) { 390 // Dead GEP's cause trouble later. Just remove them if we run into 391 // them. 392 getAnalysis<AliasAnalysis>().deleteValue(GEP); 393 GEP->eraseFromParent(); 394 // TODO: This runs the above loop over and over again for dead GEPs 395 // Couldn't we just do increment the UI iterator earlier and erase the 396 // use? 397 return isSafeToPromoteArgument(Arg, isByVal); 398 } 399 400 // Ensure that all of the indices are constants. 401 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); 402 i != e; ++i) 403 if (ConstantInt *C = dyn_cast<ConstantInt>(*i)) 404 Operands.push_back(C->getSExtValue()); 405 else 406 return false; // Not a constant operand GEP! 407 408 // Ensure that the only users of the GEP are load instructions. 409 for (Value::use_iterator UI = GEP->use_begin(), E = GEP->use_end(); 410 UI != E; ++UI) 411 if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) { 412 // Don't hack volatile/atomic loads 413 if (!LI->isSimple()) return false; 414 Loads.push_back(LI); 415 } else { 416 // Other uses than load? 417 return false; 418 } 419 } else { 420 return false; // Not a load or a GEP. 421 } 422 423 // Now, see if it is safe to promote this load / loads of this GEP. Loading 424 // is safe if Operands, or a prefix of Operands, is marked as safe. 425 if (!PrefixIn(Operands, SafeToUnconditionallyLoad)) 426 return false; 427 428 // See if we are already promoting a load with these indices. If not, check 429 // to make sure that we aren't promoting too many elements. If so, nothing 430 // to do. 431 if (ToPromote.find(Operands) == ToPromote.end()) { 432 if (maxElements > 0 && ToPromote.size() == maxElements) { 433 DEBUG(dbgs() << "argpromotion not promoting argument '" 434 << Arg->getName() << "' because it would require adding more " 435 << "than " << maxElements << " arguments to the function.\n"); 436 // We limit aggregate promotion to only promoting up to a fixed number 437 // of elements of the aggregate. 438 return false; 439 } 440 ToPromote.insert(Operands); 441 } 442 } 443 444 if (Loads.empty()) return true; // No users, this is a dead argument. 445 446 // Okay, now we know that the argument is only used by load instructions and 447 // it is safe to unconditionally perform all of them. Use alias analysis to 448 // check to see if the pointer is guaranteed to not be modified from entry of 449 // the function to each of the load instructions. 450 451 // Because there could be several/many load instructions, remember which 452 // blocks we know to be transparent to the load. 453 SmallPtrSet<BasicBlock*, 16> TranspBlocks; 454 455 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 456 457 for (unsigned i = 0, e = Loads.size(); i != e; ++i) { 458 // Check to see if the load is invalidated from the start of the block to 459 // the load itself. 460 LoadInst *Load = Loads[i]; 461 BasicBlock *BB = Load->getParent(); 462 463 AliasAnalysis::Location Loc = AA.getLocation(Load); 464 if (AA.canInstructionRangeModify(BB->front(), *Load, Loc)) 465 return false; // Pointer is invalidated! 466 467 // Now check every path from the entry block to the load for transparency. 468 // To do this, we perform a depth first search on the inverse CFG from the 469 // loading block. 470 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { 471 BasicBlock *P = *PI; 472 for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> > 473 I = idf_ext_begin(P, TranspBlocks), 474 E = idf_ext_end(P, TranspBlocks); I != E; ++I) 475 if (AA.canBasicBlockModify(**I, Loc)) 476 return false; 477 } 478 } 479 480 // If the path from the entry of the function to each load is free of 481 // instructions that potentially invalidate the load, we can make the 482 // transformation! 483 return true; 484} 485 486/// DoPromotion - This method actually performs the promotion of the specified 487/// arguments, and returns the new function. At this point, we know that it's 488/// safe to do so. 489CallGraphNode *ArgPromotion::DoPromotion(Function *F, 490 SmallPtrSet<Argument*, 8> &ArgsToPromote, 491 SmallPtrSet<Argument*, 8> &ByValArgsToTransform) { 492 493 // Start by computing a new prototype for the function, which is the same as 494 // the old function, but has modified arguments. 495 FunctionType *FTy = F->getFunctionType(); 496 std::vector<Type*> Params; 497 498 typedef std::set<IndicesVector> ScalarizeTable; 499 500 // ScalarizedElements - If we are promoting a pointer that has elements 501 // accessed out of it, keep track of which elements are accessed so that we 502 // can add one argument for each. 503 // 504 // Arguments that are directly loaded will have a zero element value here, to 505 // handle cases where there are both a direct load and GEP accesses. 506 // 507 std::map<Argument*, ScalarizeTable> ScalarizedElements; 508 509 // OriginalLoads - Keep track of a representative load instruction from the 510 // original function so that we can tell the alias analysis implementation 511 // what the new GEP/Load instructions we are inserting look like. 512 std::map<IndicesVector, LoadInst*> OriginalLoads; 513 514 // Attributes - Keep track of the parameter attributes for the arguments 515 // that we are *not* promoting. For the ones that we do promote, the parameter 516 // attributes are lost 517 SmallVector<AttributeWithIndex, 8> AttributesVec; 518 const AttrListPtr &PAL = F->getAttributes(); 519 520 // Add any return attributes. 521 Attributes attrs = PAL.getRetAttributes(); 522 if (attrs.hasAttributes()) 523 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 524 525 // First, determine the new argument list 526 unsigned ArgIndex = 1; 527 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; 528 ++I, ++ArgIndex) { 529 if (ByValArgsToTransform.count(I)) { 530 // Simple byval argument? Just add all the struct element types. 531 Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 532 StructType *STy = cast<StructType>(AgTy); 533 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) 534 Params.push_back(STy->getElementType(i)); 535 ++NumByValArgsPromoted; 536 } else if (!ArgsToPromote.count(I)) { 537 // Unchanged argument 538 Params.push_back(I->getType()); 539 Attributes attrs = PAL.getParamAttributes(ArgIndex); 540 if (attrs.hasAttributes()) 541 AttributesVec.push_back(AttributeWithIndex::get(Params.size(), attrs)); 542 } else if (I->use_empty()) { 543 // Dead argument (which are always marked as promotable) 544 ++NumArgumentsDead; 545 } else { 546 // Okay, this is being promoted. This means that the only uses are loads 547 // or GEPs which are only used by loads 548 549 // In this table, we will track which indices are loaded from the argument 550 // (where direct loads are tracked as no indices). 551 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 552 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; 553 ++UI) { 554 Instruction *User = cast<Instruction>(*UI); 555 assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User)); 556 IndicesVector Indices; 557 Indices.reserve(User->getNumOperands() - 1); 558 // Since loads will only have a single operand, and GEPs only a single 559 // non-index operand, this will record direct loads without any indices, 560 // and gep+loads with the GEP indices. 561 for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end(); 562 II != IE; ++II) 563 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue()); 564 // GEPs with a single 0 index can be merged with direct loads 565 if (Indices.size() == 1 && Indices.front() == 0) 566 Indices.clear(); 567 ArgIndices.insert(Indices); 568 LoadInst *OrigLoad; 569 if (LoadInst *L = dyn_cast<LoadInst>(User)) 570 OrigLoad = L; 571 else 572 // Take any load, we will use it only to update Alias Analysis 573 OrigLoad = cast<LoadInst>(User->use_back()); 574 OriginalLoads[Indices] = OrigLoad; 575 } 576 577 // Add a parameter to the function for each element passed in. 578 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 579 E = ArgIndices.end(); SI != E; ++SI) { 580 // not allowed to dereference ->begin() if size() is 0 581 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI)); 582 assert(Params.back()); 583 } 584 585 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty()) 586 ++NumArgumentsPromoted; 587 else 588 ++NumAggregatesPromoted; 589 } 590 } 591 592 // Add any function attributes. 593 attrs = PAL.getFnAttributes(); 594 if (attrs.hasAttributes()) 595 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 596 597 Type *RetTy = FTy->getReturnType(); 598 599 // Construct the new function type using the new arguments. 600 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); 601 602 // Create the new function body and insert it into the module. 603 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); 604 NF->copyAttributesFrom(F); 605 606 607 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n" 608 << "From: " << *F); 609 610 // Recompute the parameter attributes list based on the new arguments for 611 // the function. 612 NF->setAttributes(AttrListPtr::get(AttributesVec)); 613 AttributesVec.clear(); 614 615 F->getParent()->getFunctionList().insert(F, NF); 616 NF->takeName(F); 617 618 // Get the alias analysis information that we need to update to reflect our 619 // changes. 620 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 621 622 // Get the callgraph information that we need to update to reflect our 623 // changes. 624 CallGraph &CG = getAnalysis<CallGraph>(); 625 626 // Get a new callgraph node for NF. 627 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF); 628 629 // Loop over all of the callers of the function, transforming the call sites 630 // to pass in the loaded pointers. 631 // 632 SmallVector<Value*, 16> Args; 633 while (!F->use_empty()) { 634 CallSite CS(F->use_back()); 635 assert(CS.getCalledFunction() == F); 636 Instruction *Call = CS.getInstruction(); 637 const AttrListPtr &CallPAL = CS.getAttributes(); 638 639 // Add any return attributes. 640 Attributes attrs = CallPAL.getRetAttributes(); 641 if (attrs.hasAttributes()) 642 AttributesVec.push_back(AttributeWithIndex::get(0, attrs)); 643 644 // Loop over the operands, inserting GEP and loads in the caller as 645 // appropriate. 646 CallSite::arg_iterator AI = CS.arg_begin(); 647 ArgIndex = 1; 648 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 649 I != E; ++I, ++AI, ++ArgIndex) 650 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 651 Args.push_back(*AI); // Unmodified argument 652 653 Attributes Attrs = CallPAL.getParamAttributes(ArgIndex); 654 if (Attrs.hasAttributes()) 655 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 656 657 } else if (ByValArgsToTransform.count(I)) { 658 // Emit a GEP and load for each element of the struct. 659 Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 660 StructType *STy = cast<StructType>(AgTy); 661 Value *Idxs[2] = { 662 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 663 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 664 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 665 Value *Idx = GetElementPtrInst::Create(*AI, Idxs, 666 (*AI)->getName()+"."+utostr(i), 667 Call); 668 // TODO: Tell AA about the new values? 669 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); 670 } 671 } else if (!I->use_empty()) { 672 // Non-dead argument: insert GEPs and loads as appropriate. 673 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 674 // Store the Value* version of the indices in here, but declare it now 675 // for reuse. 676 std::vector<Value*> Ops; 677 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 678 E = ArgIndices.end(); SI != E; ++SI) { 679 Value *V = *AI; 680 LoadInst *OrigLoad = OriginalLoads[*SI]; 681 if (!SI->empty()) { 682 Ops.reserve(SI->size()); 683 Type *ElTy = V->getType(); 684 for (IndicesVector::const_iterator II = SI->begin(), 685 IE = SI->end(); II != IE; ++II) { 686 // Use i32 to index structs, and i64 for others (pointers/arrays). 687 // This satisfies GEP constraints. 688 Type *IdxTy = (ElTy->isStructTy() ? 689 Type::getInt32Ty(F->getContext()) : 690 Type::getInt64Ty(F->getContext())); 691 Ops.push_back(ConstantInt::get(IdxTy, *II)); 692 // Keep track of the type we're currently indexing. 693 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II); 694 } 695 // And create a GEP to extract those indices. 696 V = GetElementPtrInst::Create(V, Ops, V->getName()+".idx", Call); 697 Ops.clear(); 698 AA.copyValue(OrigLoad->getOperand(0), V); 699 } 700 // Since we're replacing a load make sure we take the alignment 701 // of the previous load. 702 LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call); 703 newLoad->setAlignment(OrigLoad->getAlignment()); 704 // Transfer the TBAA info too. 705 newLoad->setMetadata(LLVMContext::MD_tbaa, 706 OrigLoad->getMetadata(LLVMContext::MD_tbaa)); 707 Args.push_back(newLoad); 708 AA.copyValue(OrigLoad, Args.back()); 709 } 710 } 711 712 // Push any varargs arguments on the list. 713 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { 714 Args.push_back(*AI); 715 Attributes Attrs = CallPAL.getParamAttributes(ArgIndex); 716 if (Attrs.hasAttributes()) 717 AttributesVec.push_back(AttributeWithIndex::get(Args.size(), Attrs)); 718 } 719 720 // Add any function attributes. 721 attrs = CallPAL.getFnAttributes(); 722 if (attrs.hasAttributes()) 723 AttributesVec.push_back(AttributeWithIndex::get(~0, attrs)); 724 725 Instruction *New; 726 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 727 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 728 Args, "", Call); 729 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 730 cast<InvokeInst>(New)->setAttributes(AttrListPtr::get(AttributesVec)); 731 } else { 732 New = CallInst::Create(NF, Args, "", Call); 733 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 734 cast<CallInst>(New)->setAttributes(AttrListPtr::get(AttributesVec)); 735 if (cast<CallInst>(Call)->isTailCall()) 736 cast<CallInst>(New)->setTailCall(); 737 } 738 Args.clear(); 739 AttributesVec.clear(); 740 741 // Update the alias analysis implementation to know that we are replacing 742 // the old call with a new one. 743 AA.replaceWithNewValue(Call, New); 744 745 // Update the callgraph to know that the callsite has been transformed. 746 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()]; 747 CalleeNode->replaceCallEdge(Call, New, NF_CGN); 748 749 if (!Call->use_empty()) { 750 Call->replaceAllUsesWith(New); 751 New->takeName(Call); 752 } 753 754 // Finally, remove the old call from the program, reducing the use-count of 755 // F. 756 Call->eraseFromParent(); 757 } 758 759 // Since we have now created the new function, splice the body of the old 760 // function right into the new function, leaving the old rotting hulk of the 761 // function empty. 762 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 763 764 // Loop over the argument list, transferring uses of the old arguments over to 765 // the new arguments, also transferring over the names as well. 766 // 767 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 768 I2 = NF->arg_begin(); I != E; ++I) { 769 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 770 // If this is an unmodified argument, move the name and users over to the 771 // new version. 772 I->replaceAllUsesWith(I2); 773 I2->takeName(I); 774 AA.replaceWithNewValue(I, I2); 775 ++I2; 776 continue; 777 } 778 779 if (ByValArgsToTransform.count(I)) { 780 // In the callee, we create an alloca, and store each of the new incoming 781 // arguments into the alloca. 782 Instruction *InsertPt = NF->begin()->begin(); 783 784 // Just add all the struct element types. 785 Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 786 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 787 StructType *STy = cast<StructType>(AgTy); 788 Value *Idxs[2] = { 789 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 790 791 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 792 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 793 Value *Idx = 794 GetElementPtrInst::Create(TheAlloca, Idxs, 795 TheAlloca->getName()+"."+Twine(i), 796 InsertPt); 797 I2->setName(I->getName()+"."+Twine(i)); 798 new StoreInst(I2++, Idx, InsertPt); 799 } 800 801 // Anything that used the arg should now use the alloca. 802 I->replaceAllUsesWith(TheAlloca); 803 TheAlloca->takeName(I); 804 AA.replaceWithNewValue(I, TheAlloca); 805 continue; 806 } 807 808 if (I->use_empty()) { 809 AA.deleteValue(I); 810 continue; 811 } 812 813 // Otherwise, if we promoted this argument, then all users are load 814 // instructions (or GEPs with only load users), and all loads should be 815 // using the new argument that we added. 816 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 817 818 while (!I->use_empty()) { 819 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 820 assert(ArgIndices.begin()->empty() && 821 "Load element should sort to front!"); 822 I2->setName(I->getName()+".val"); 823 LI->replaceAllUsesWith(I2); 824 AA.replaceWithNewValue(LI, I2); 825 LI->eraseFromParent(); 826 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName() 827 << "' in function '" << F->getName() << "'\n"); 828 } else { 829 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 830 IndicesVector Operands; 831 Operands.reserve(GEP->getNumIndices()); 832 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 833 II != IE; ++II) 834 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); 835 836 // GEPs with a single 0 index can be merged with direct loads 837 if (Operands.size() == 1 && Operands.front() == 0) 838 Operands.clear(); 839 840 Function::arg_iterator TheArg = I2; 841 for (ScalarizeTable::iterator It = ArgIndices.begin(); 842 *It != Operands; ++It, ++TheArg) { 843 assert(It != ArgIndices.end() && "GEP not handled??"); 844 } 845 846 std::string NewName = I->getName(); 847 for (unsigned i = 0, e = Operands.size(); i != e; ++i) { 848 NewName += "." + utostr(Operands[i]); 849 } 850 NewName += ".val"; 851 TheArg->setName(NewName); 852 853 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName() 854 << "' of function '" << NF->getName() << "'\n"); 855 856 // All of the uses must be load instructions. Replace them all with 857 // the argument specified by ArgNo. 858 while (!GEP->use_empty()) { 859 LoadInst *L = cast<LoadInst>(GEP->use_back()); 860 L->replaceAllUsesWith(TheArg); 861 AA.replaceWithNewValue(L, TheArg); 862 L->eraseFromParent(); 863 } 864 AA.deleteValue(GEP); 865 GEP->eraseFromParent(); 866 } 867 } 868 869 // Increment I2 past all of the arguments added for this promoted pointer. 870 std::advance(I2, ArgIndices.size()); 871 } 872 873 // Tell the alias analysis that the old function is about to disappear. 874 AA.replaceWithNewValue(F, NF); 875 876 877 NF_CGN->stealCalledFunctionsFrom(CG[F]); 878 879 // Now that the old function is dead, delete it. If there is a dangling 880 // reference to the CallgraphNode, just leave the dead function around for 881 // someone else to nuke. 882 CallGraphNode *CGN = CG[F]; 883 if (CGN->getNumReferences() == 0) 884 delete CG.removeFunctionFromModule(CGN); 885 else 886 F->setLinkage(Function::ExternalLinkage); 887 888 return NF_CGN; 889} 890