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/ADT/DepthFirstIterator.h" 35 #include "llvm/ADT/Statistic.h" 36 #include "llvm/ADT/StringExtras.h" 37 #include "llvm/Analysis/AliasAnalysis.h" 38 #include "llvm/Analysis/CallGraph.h" 39 #include "llvm/Analysis/CallGraphSCCPass.h" 40 #include "llvm/IR/Constants.h" 41 #include "llvm/IR/DerivedTypes.h" 42 #include "llvm/IR/Instructions.h" 43 #include "llvm/IR/LLVMContext.h" 44 #include "llvm/IR/Module.h" 45 #include "llvm/Support/CFG.h" 46 #include "llvm/Support/CallSite.h" 47 #include "llvm/Support/Debug.h" 48 #include "llvm/Support/raw_ostream.h" 49 #include <set> 50 using namespace llvm; 51 52 STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted"); 53 STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted"); 54 STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted"); 55 STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated"); 56 57 namespace { 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 87 char ArgPromotion::ID = 0; 88 INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion", 89 "Promote 'by reference' arguments to scalars", false, false) 90 INITIALIZE_AG_DEPENDENCY(AliasAnalysis) 91 INITIALIZE_AG_DEPENDENCY(CallGraph) 92 INITIALIZE_PASS_END(ArgPromotion, "argpromotion", 93 "Promote 'by reference' arguments to scalars", false, false) 94 95 Pass *llvm::createArgumentPromotionPass(unsigned maxElements) { 96 return new ArgPromotion(maxElements); 97 } 98 99 bool 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 /// 122 CallGraphNode *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->getAttributes(). 157 hasAttribute(PointerArgs[i].second+1, Attribute::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. 221 static 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! 245 static 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. 254 static 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). 273 static 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. 309 bool 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. 489 CallGraphNode *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 // Attribute - 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<AttributeSet, 8> AttributesVec; 518 const AttributeSet &PAL = F->getAttributes(); 519 520 // Add any return attributes. 521 if (PAL.hasAttributes(AttributeSet::ReturnIndex)) 522 AttributesVec.push_back(AttributeSet::get(F->getContext(), 523 PAL.getRetAttributes())); 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 AttributeSet attrs = PAL.getParamAttributes(ArgIndex); 540 if (attrs.hasAttributes(ArgIndex)) { 541 AttrBuilder B(attrs, ArgIndex); 542 AttributesVec. 543 push_back(AttributeSet::get(F->getContext(), Params.size(), B)); 544 } 545 } else if (I->use_empty()) { 546 // Dead argument (which are always marked as promotable) 547 ++NumArgumentsDead; 548 } else { 549 // Okay, this is being promoted. This means that the only uses are loads 550 // or GEPs which are only used by loads 551 552 // In this table, we will track which indices are loaded from the argument 553 // (where direct loads are tracked as no indices). 554 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 555 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI != E; 556 ++UI) { 557 Instruction *User = cast<Instruction>(*UI); 558 assert(isa<LoadInst>(User) || isa<GetElementPtrInst>(User)); 559 IndicesVector Indices; 560 Indices.reserve(User->getNumOperands() - 1); 561 // Since loads will only have a single operand, and GEPs only a single 562 // non-index operand, this will record direct loads without any indices, 563 // and gep+loads with the GEP indices. 564 for (User::op_iterator II = User->op_begin() + 1, IE = User->op_end(); 565 II != IE; ++II) 566 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue()); 567 // GEPs with a single 0 index can be merged with direct loads 568 if (Indices.size() == 1 && Indices.front() == 0) 569 Indices.clear(); 570 ArgIndices.insert(Indices); 571 LoadInst *OrigLoad; 572 if (LoadInst *L = dyn_cast<LoadInst>(User)) 573 OrigLoad = L; 574 else 575 // Take any load, we will use it only to update Alias Analysis 576 OrigLoad = cast<LoadInst>(User->use_back()); 577 OriginalLoads[Indices] = OrigLoad; 578 } 579 580 // Add a parameter to the function for each element passed in. 581 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 582 E = ArgIndices.end(); SI != E; ++SI) { 583 // not allowed to dereference ->begin() if size() is 0 584 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI)); 585 assert(Params.back()); 586 } 587 588 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty()) 589 ++NumArgumentsPromoted; 590 else 591 ++NumAggregatesPromoted; 592 } 593 } 594 595 // Add any function attributes. 596 if (PAL.hasAttributes(AttributeSet::FunctionIndex)) 597 AttributesVec.push_back(AttributeSet::get(FTy->getContext(), 598 PAL.getFnAttributes())); 599 600 Type *RetTy = FTy->getReturnType(); 601 602 // Construct the new function type using the new arguments. 603 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg()); 604 605 // Create the new function body and insert it into the module. 606 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName()); 607 NF->copyAttributesFrom(F); 608 609 610 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n" 611 << "From: " << *F); 612 613 // Recompute the parameter attributes list based on the new arguments for 614 // the function. 615 NF->setAttributes(AttributeSet::get(F->getContext(), AttributesVec)); 616 AttributesVec.clear(); 617 618 F->getParent()->getFunctionList().insert(F, NF); 619 NF->takeName(F); 620 621 // Get the alias analysis information that we need to update to reflect our 622 // changes. 623 AliasAnalysis &AA = getAnalysis<AliasAnalysis>(); 624 625 // Get the callgraph information that we need to update to reflect our 626 // changes. 627 CallGraph &CG = getAnalysis<CallGraph>(); 628 629 // Get a new callgraph node for NF. 630 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF); 631 632 // Loop over all of the callers of the function, transforming the call sites 633 // to pass in the loaded pointers. 634 // 635 SmallVector<Value*, 16> Args; 636 while (!F->use_empty()) { 637 CallSite CS(F->use_back()); 638 assert(CS.getCalledFunction() == F); 639 Instruction *Call = CS.getInstruction(); 640 const AttributeSet &CallPAL = CS.getAttributes(); 641 642 // Add any return attributes. 643 if (CallPAL.hasAttributes(AttributeSet::ReturnIndex)) 644 AttributesVec.push_back(AttributeSet::get(F->getContext(), 645 CallPAL.getRetAttributes())); 646 647 // Loop over the operands, inserting GEP and loads in the caller as 648 // appropriate. 649 CallSite::arg_iterator AI = CS.arg_begin(); 650 ArgIndex = 1; 651 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); 652 I != E; ++I, ++AI, ++ArgIndex) 653 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 654 Args.push_back(*AI); // Unmodified argument 655 656 if (CallPAL.hasAttributes(ArgIndex)) { 657 AttrBuilder B(CallPAL, ArgIndex); 658 AttributesVec. 659 push_back(AttributeSet::get(F->getContext(), Args.size(), B)); 660 } 661 } else if (ByValArgsToTransform.count(I)) { 662 // Emit a GEP and load for each element of the struct. 663 Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 664 StructType *STy = cast<StructType>(AgTy); 665 Value *Idxs[2] = { 666 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 667 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 668 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 669 Value *Idx = GetElementPtrInst::Create(*AI, Idxs, 670 (*AI)->getName()+"."+utostr(i), 671 Call); 672 // TODO: Tell AA about the new values? 673 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call)); 674 } 675 } else if (!I->use_empty()) { 676 // Non-dead argument: insert GEPs and loads as appropriate. 677 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 678 // Store the Value* version of the indices in here, but declare it now 679 // for reuse. 680 std::vector<Value*> Ops; 681 for (ScalarizeTable::iterator SI = ArgIndices.begin(), 682 E = ArgIndices.end(); SI != E; ++SI) { 683 Value *V = *AI; 684 LoadInst *OrigLoad = OriginalLoads[*SI]; 685 if (!SI->empty()) { 686 Ops.reserve(SI->size()); 687 Type *ElTy = V->getType(); 688 for (IndicesVector::const_iterator II = SI->begin(), 689 IE = SI->end(); II != IE; ++II) { 690 // Use i32 to index structs, and i64 for others (pointers/arrays). 691 // This satisfies GEP constraints. 692 Type *IdxTy = (ElTy->isStructTy() ? 693 Type::getInt32Ty(F->getContext()) : 694 Type::getInt64Ty(F->getContext())); 695 Ops.push_back(ConstantInt::get(IdxTy, *II)); 696 // Keep track of the type we're currently indexing. 697 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II); 698 } 699 // And create a GEP to extract those indices. 700 V = GetElementPtrInst::Create(V, Ops, V->getName()+".idx", Call); 701 Ops.clear(); 702 AA.copyValue(OrigLoad->getOperand(0), V); 703 } 704 // Since we're replacing a load make sure we take the alignment 705 // of the previous load. 706 LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call); 707 newLoad->setAlignment(OrigLoad->getAlignment()); 708 // Transfer the TBAA info too. 709 newLoad->setMetadata(LLVMContext::MD_tbaa, 710 OrigLoad->getMetadata(LLVMContext::MD_tbaa)); 711 Args.push_back(newLoad); 712 AA.copyValue(OrigLoad, Args.back()); 713 } 714 } 715 716 // Push any varargs arguments on the list. 717 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) { 718 Args.push_back(*AI); 719 if (CallPAL.hasAttributes(ArgIndex)) { 720 AttrBuilder B(CallPAL, ArgIndex); 721 AttributesVec. 722 push_back(AttributeSet::get(F->getContext(), Args.size(), B)); 723 } 724 } 725 726 // Add any function attributes. 727 if (CallPAL.hasAttributes(AttributeSet::FunctionIndex)) 728 AttributesVec.push_back(AttributeSet::get(Call->getContext(), 729 CallPAL.getFnAttributes())); 730 731 Instruction *New; 732 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) { 733 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(), 734 Args, "", Call); 735 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv()); 736 cast<InvokeInst>(New)->setAttributes(AttributeSet::get(II->getContext(), 737 AttributesVec)); 738 } else { 739 New = CallInst::Create(NF, Args, "", Call); 740 cast<CallInst>(New)->setCallingConv(CS.getCallingConv()); 741 cast<CallInst>(New)->setAttributes(AttributeSet::get(New->getContext(), 742 AttributesVec)); 743 if (cast<CallInst>(Call)->isTailCall()) 744 cast<CallInst>(New)->setTailCall(); 745 } 746 Args.clear(); 747 AttributesVec.clear(); 748 749 // Update the alias analysis implementation to know that we are replacing 750 // the old call with a new one. 751 AA.replaceWithNewValue(Call, New); 752 753 // Update the callgraph to know that the callsite has been transformed. 754 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()]; 755 CalleeNode->replaceCallEdge(Call, New, NF_CGN); 756 757 if (!Call->use_empty()) { 758 Call->replaceAllUsesWith(New); 759 New->takeName(Call); 760 } 761 762 // Finally, remove the old call from the program, reducing the use-count of 763 // F. 764 Call->eraseFromParent(); 765 } 766 767 // Since we have now created the new function, splice the body of the old 768 // function right into the new function, leaving the old rotting hulk of the 769 // function empty. 770 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList()); 771 772 // Loop over the argument list, transferring uses of the old arguments over to 773 // the new arguments, also transferring over the names as well. 774 // 775 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(), 776 I2 = NF->arg_begin(); I != E; ++I) { 777 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) { 778 // If this is an unmodified argument, move the name and users over to the 779 // new version. 780 I->replaceAllUsesWith(I2); 781 I2->takeName(I); 782 AA.replaceWithNewValue(I, I2); 783 ++I2; 784 continue; 785 } 786 787 if (ByValArgsToTransform.count(I)) { 788 // In the callee, we create an alloca, and store each of the new incoming 789 // arguments into the alloca. 790 Instruction *InsertPt = NF->begin()->begin(); 791 792 // Just add all the struct element types. 793 Type *AgTy = cast<PointerType>(I->getType())->getElementType(); 794 Value *TheAlloca = new AllocaInst(AgTy, 0, "", InsertPt); 795 StructType *STy = cast<StructType>(AgTy); 796 Value *Idxs[2] = { 797 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), 0 }; 798 799 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) { 800 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i); 801 Value *Idx = 802 GetElementPtrInst::Create(TheAlloca, Idxs, 803 TheAlloca->getName()+"."+Twine(i), 804 InsertPt); 805 I2->setName(I->getName()+"."+Twine(i)); 806 new StoreInst(I2++, Idx, InsertPt); 807 } 808 809 // Anything that used the arg should now use the alloca. 810 I->replaceAllUsesWith(TheAlloca); 811 TheAlloca->takeName(I); 812 AA.replaceWithNewValue(I, TheAlloca); 813 continue; 814 } 815 816 if (I->use_empty()) { 817 AA.deleteValue(I); 818 continue; 819 } 820 821 // Otherwise, if we promoted this argument, then all users are load 822 // instructions (or GEPs with only load users), and all loads should be 823 // using the new argument that we added. 824 ScalarizeTable &ArgIndices = ScalarizedElements[I]; 825 826 while (!I->use_empty()) { 827 if (LoadInst *LI = dyn_cast<LoadInst>(I->use_back())) { 828 assert(ArgIndices.begin()->empty() && 829 "Load element should sort to front!"); 830 I2->setName(I->getName()+".val"); 831 LI->replaceAllUsesWith(I2); 832 AA.replaceWithNewValue(LI, I2); 833 LI->eraseFromParent(); 834 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName() 835 << "' in function '" << F->getName() << "'\n"); 836 } else { 837 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->use_back()); 838 IndicesVector Operands; 839 Operands.reserve(GEP->getNumIndices()); 840 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end(); 841 II != IE; ++II) 842 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue()); 843 844 // GEPs with a single 0 index can be merged with direct loads 845 if (Operands.size() == 1 && Operands.front() == 0) 846 Operands.clear(); 847 848 Function::arg_iterator TheArg = I2; 849 for (ScalarizeTable::iterator It = ArgIndices.begin(); 850 *It != Operands; ++It, ++TheArg) { 851 assert(It != ArgIndices.end() && "GEP not handled??"); 852 } 853 854 std::string NewName = I->getName(); 855 for (unsigned i = 0, e = Operands.size(); i != e; ++i) { 856 NewName += "." + utostr(Operands[i]); 857 } 858 NewName += ".val"; 859 TheArg->setName(NewName); 860 861 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName() 862 << "' of function '" << NF->getName() << "'\n"); 863 864 // All of the uses must be load instructions. Replace them all with 865 // the argument specified by ArgNo. 866 while (!GEP->use_empty()) { 867 LoadInst *L = cast<LoadInst>(GEP->use_back()); 868 L->replaceAllUsesWith(TheArg); 869 AA.replaceWithNewValue(L, TheArg); 870 L->eraseFromParent(); 871 } 872 AA.deleteValue(GEP); 873 GEP->eraseFromParent(); 874 } 875 } 876 877 // Increment I2 past all of the arguments added for this promoted pointer. 878 std::advance(I2, ArgIndices.size()); 879 } 880 881 // Tell the alias analysis that the old function is about to disappear. 882 AA.replaceWithNewValue(F, NF); 883 884 885 NF_CGN->stealCalledFunctionsFrom(CG[F]); 886 887 // Now that the old function is dead, delete it. If there is a dangling 888 // reference to the CallgraphNode, just leave the dead function around for 889 // someone else to nuke. 890 CallGraphNode *CGN = CG[F]; 891 if (CGN->getNumReferences() == 0) 892 delete CG.removeFunctionFromModule(CGN); 893 else 894 F->setLinkage(Function::ExternalLinkage); 895 896 return NF_CGN; 897 } 898