1 //===-- ArgumentPromotion.cpp - Promote by-reference arguments ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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).
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.
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.
30 //===----------------------------------------------------------------------===//
32 #include "llvm/Transforms/IPO.h"
33 #include "llvm/ADT/DepthFirstIterator.h"
34 #include "llvm/ADT/Statistic.h"
35 #include "llvm/ADT/StringExtras.h"
36 #include "llvm/Analysis/AliasAnalysis.h"
37 #include "llvm/Analysis/CallGraph.h"
38 #include "llvm/Analysis/CallGraphSCCPass.h"
39 #include "llvm/IR/CFG.h"
40 #include "llvm/IR/CallSite.h"
41 #include "llvm/IR/Constants.h"
42 #include "llvm/IR/DerivedTypes.h"
43 #include "llvm/IR/Instructions.h"
44 #include "llvm/IR/LLVMContext.h"
45 #include "llvm/IR/Module.h"
46 #include "llvm/Support/Debug.h"
47 #include "llvm/Support/raw_ostream.h"
51 #define DEBUG_TYPE "argpromotion"
53 STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted");
54 STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
55 STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted");
56 STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated");
59 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
61 struct ArgPromotion : public CallGraphSCCPass {
62 void getAnalysisUsage(AnalysisUsage &AU) const override {
63 AU.addRequired<AliasAnalysis>();
64 CallGraphSCCPass::getAnalysisUsage(AU);
67 bool runOnSCC(CallGraphSCC &SCC) override;
68 static char ID; // Pass identification, replacement for typeid
69 explicit ArgPromotion(unsigned maxElements = 3)
70 : CallGraphSCCPass(ID), maxElements(maxElements) {
71 initializeArgPromotionPass(*PassRegistry::getPassRegistry());
74 /// A vector used to hold the indices of a single GEP instruction
75 typedef std::vector<uint64_t> IndicesVector;
78 CallGraphNode *PromoteArguments(CallGraphNode *CGN);
79 bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const;
80 CallGraphNode *DoPromotion(Function *F,
81 SmallPtrSet<Argument*, 8> &ArgsToPromote,
82 SmallPtrSet<Argument*, 8> &ByValArgsToTransform);
83 /// The maximum number of elements to expand, or 0 for unlimited.
88 char ArgPromotion::ID = 0;
89 INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion",
90 "Promote 'by reference' arguments to scalars", false, false)
91 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
92 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
93 INITIALIZE_PASS_END(ArgPromotion, "argpromotion",
94 "Promote 'by reference' arguments to scalars", false, false)
96 Pass *llvm::createArgumentPromotionPass(unsigned maxElements) {
97 return new ArgPromotion(maxElements);
100 bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) {
101 bool Changed = false, LocalChange;
103 do { // Iterate until we stop promoting from this SCC.
105 // Attempt to promote arguments from all functions in this SCC.
106 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
107 if (CallGraphNode *CGN = PromoteArguments(*I)) {
109 SCC.ReplaceNode(*I, CGN);
112 Changed |= LocalChange; // Remember that we changed something.
113 } while (LocalChange);
118 /// PromoteArguments - This method checks the specified function to see if there
119 /// are any promotable arguments and if it is safe to promote the function (for
120 /// example, all callers are direct). If safe to promote some arguments, it
121 /// calls the DoPromotion method.
123 CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
124 Function *F = CGN->getFunction();
126 // Make sure that it is local to this module.
127 if (!F || !F->hasLocalLinkage()) return nullptr;
129 // First check: see if there are any pointer arguments! If not, quick exit.
130 SmallVector<Argument*, 16> PointerArgs;
131 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
132 if (I->getType()->isPointerTy())
133 PointerArgs.push_back(I);
134 if (PointerArgs.empty()) return nullptr;
136 // Second check: make sure that all callers are direct callers. We can't
137 // transform functions that have indirect callers. Also see if the function
138 // is self-recursive.
139 bool isSelfRecursive = false;
140 for (Use &U : F->uses()) {
141 CallSite CS(U.getUser());
142 // Must be a direct call.
143 if (CS.getInstruction() == nullptr || !CS.isCallee(&U)) return nullptr;
145 if (CS.getInstruction()->getParent()->getParent() == F)
146 isSelfRecursive = true;
149 // Check to see which arguments are promotable. If an argument is promotable,
150 // add it to ArgsToPromote.
151 SmallPtrSet<Argument*, 8> ArgsToPromote;
152 SmallPtrSet<Argument*, 8> ByValArgsToTransform;
153 for (unsigned i = 0, e = PointerArgs.size(); i != e; ++i) {
154 Argument *PtrArg = PointerArgs[i];
155 Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
157 // If this is a byval argument, and if the aggregate type is small, just
158 // pass the elements, which is always safe. This does not apply to
160 if (PtrArg->hasByValAttr()) {
161 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
162 if (maxElements > 0 && STy->getNumElements() > maxElements) {
163 DEBUG(dbgs() << "argpromotion disable promoting argument '"
164 << PtrArg->getName() << "' because it would require adding more"
165 << " than " << maxElements << " arguments to the function.\n");
169 // If all the elements are single-value types, we can promote it.
170 bool AllSimple = true;
171 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
172 if (!STy->getElementType(i)->isSingleValueType()) {
178 // Safe to transform, don't even bother trying to "promote" it.
179 // Passing the elements as a scalar will allow scalarrepl to hack on
180 // the new alloca we introduce.
182 ByValArgsToTransform.insert(PtrArg);
188 // If the argument is a recursive type and we're in a recursive
189 // function, we could end up infinitely peeling the function argument.
190 if (isSelfRecursive) {
191 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
192 bool RecursiveType = false;
193 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
194 if (STy->getElementType(i) == PtrArg->getType()) {
195 RecursiveType = true;
204 // Otherwise, see if we can promote the pointer to its value.
205 if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValOrInAllocaAttr()))
206 ArgsToPromote.insert(PtrArg);
209 // No promotable pointer arguments.
210 if (ArgsToPromote.empty() && ByValArgsToTransform.empty())
213 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform);
216 /// AllCallersPassInValidPointerForArgument - Return true if we can prove that
217 /// all callees pass in a valid pointer for the specified function argument.
218 static bool AllCallersPassInValidPointerForArgument(Argument *Arg) {
219 Function *Callee = Arg->getParent();
221 unsigned ArgNo = Arg->getArgNo();
223 // Look at all call sites of the function. At this pointer we know we only
224 // have direct callees.
225 for (User *U : Callee->users()) {
227 assert(CS && "Should only have direct calls!");
229 if (!CS.getArgument(ArgNo)->isDereferenceablePointer())
235 /// Returns true if Prefix is a prefix of longer. That means, Longer has a size
236 /// that is greater than or equal to the size of prefix, and each of the
237 /// elements in Prefix is the same as the corresponding elements in Longer.
239 /// This means it also returns true when Prefix and Longer are equal!
240 static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix,
241 const ArgPromotion::IndicesVector &Longer) {
242 if (Prefix.size() > Longer.size())
244 return std::equal(Prefix.begin(), Prefix.end(), Longer.begin());
248 /// Checks if Indices, or a prefix of Indices, is in Set.
249 static bool PrefixIn(const ArgPromotion::IndicesVector &Indices,
250 std::set<ArgPromotion::IndicesVector> &Set) {
251 std::set<ArgPromotion::IndicesVector>::iterator Low;
252 Low = Set.upper_bound(Indices);
253 if (Low != Set.begin())
255 // Low is now the last element smaller than or equal to Indices. This means
256 // it points to a prefix of Indices (possibly Indices itself), if such
259 // This load is safe if any prefix of its operands is safe to load.
260 return Low != Set.end() && IsPrefix(*Low, Indices);
263 /// Mark the given indices (ToMark) as safe in the given set of indices
264 /// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
265 /// is already a prefix of Indices in Safe, Indices are implicitely marked safe
266 /// already. Furthermore, any indices that Indices is itself a prefix of, are
267 /// removed from Safe (since they are implicitely safe because of Indices now).
268 static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark,
269 std::set<ArgPromotion::IndicesVector> &Safe) {
270 std::set<ArgPromotion::IndicesVector>::iterator Low;
271 Low = Safe.upper_bound(ToMark);
272 // Guard against the case where Safe is empty
273 if (Low != Safe.begin())
275 // Low is now the last element smaller than or equal to Indices. This
276 // means it points to a prefix of Indices (possibly Indices itself), if
277 // such prefix exists.
278 if (Low != Safe.end()) {
279 if (IsPrefix(*Low, ToMark))
280 // If there is already a prefix of these indices (or exactly these
281 // indices) marked a safe, don't bother adding these indices
284 // Increment Low, so we can use it as a "insert before" hint
288 Low = Safe.insert(Low, ToMark);
290 // If there we're a prefix of longer index list(s), remove those
291 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end();
292 while (Low != End && IsPrefix(ToMark, *Low)) {
293 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low;
299 /// isSafeToPromoteArgument - As you might guess from the name of this method,
300 /// it checks to see if it is both safe and useful to promote the argument.
301 /// This method limits promotion of aggregates to only promote up to three
302 /// elements of the aggregate in order to avoid exploding the number of
303 /// arguments passed in.
304 bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg,
305 bool isByValOrInAlloca) const {
306 typedef std::set<IndicesVector> GEPIndicesSet;
308 // Quick exit for unused arguments
309 if (Arg->use_empty())
312 // We can only promote this argument if all of the uses are loads, or are GEP
313 // instructions (with constant indices) that are subsequently loaded.
315 // Promoting the argument causes it to be loaded in the caller
316 // unconditionally. This is only safe if we can prove that either the load
317 // would have happened in the callee anyway (ie, there is a load in the entry
318 // block) or the pointer passed in at every call site is guaranteed to be
320 // In the former case, invalid loads can happen, but would have happened
321 // anyway, in the latter case, invalid loads won't happen. This prevents us
322 // from introducing an invalid load that wouldn't have happened in the
325 // This set will contain all sets of indices that are loaded in the entry
326 // block, and thus are safe to unconditionally load in the caller.
328 // This optimization is also safe for InAlloca parameters, because it verifies
329 // that the address isn't captured.
330 GEPIndicesSet SafeToUnconditionallyLoad;
332 // This set contains all the sets of indices that we are planning to promote.
333 // This makes it possible to limit the number of arguments added.
334 GEPIndicesSet ToPromote;
336 // If the pointer is always valid, any load with first index 0 is valid.
337 if (isByValOrInAlloca || AllCallersPassInValidPointerForArgument(Arg))
338 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
340 // First, iterate the entry block and mark loads of (geps of) arguments as
342 BasicBlock *EntryBlock = Arg->getParent()->begin();
343 // Declare this here so we can reuse it
344 IndicesVector Indices;
345 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end();
347 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
348 Value *V = LI->getPointerOperand();
349 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
350 V = GEP->getPointerOperand();
352 // This load actually loads (part of) Arg? Check the indices then.
353 Indices.reserve(GEP->getNumIndices());
354 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
356 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
357 Indices.push_back(CI->getSExtValue());
359 // We found a non-constant GEP index for this argument? Bail out
360 // right away, can't promote this argument at all.
363 // Indices checked out, mark them as safe
364 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad);
367 } else if (V == Arg) {
368 // Direct loads are equivalent to a GEP with a single 0 index.
369 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
373 // Now, iterate all uses of the argument to see if there are any uses that are
374 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
375 SmallVector<LoadInst*, 16> Loads;
376 IndicesVector Operands;
377 for (Use &U : Arg->uses()) {
378 User *UR = U.getUser();
380 if (LoadInst *LI = dyn_cast<LoadInst>(UR)) {
381 // Don't hack volatile/atomic loads
382 if (!LI->isSimple()) return false;
384 // Direct loads are equivalent to a GEP with a zero index and then a load.
385 Operands.push_back(0);
386 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UR)) {
387 if (GEP->use_empty()) {
388 // Dead GEP's cause trouble later. Just remove them if we run into
390 getAnalysis<AliasAnalysis>().deleteValue(GEP);
391 GEP->eraseFromParent();
392 // TODO: This runs the above loop over and over again for dead GEPs
393 // Couldn't we just do increment the UI iterator earlier and erase the
395 return isSafeToPromoteArgument(Arg, isByValOrInAlloca);
398 // Ensure that all of the indices are constants.
399 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end();
401 if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
402 Operands.push_back(C->getSExtValue());
404 return false; // Not a constant operand GEP!
406 // Ensure that the only users of the GEP are load instructions.
407 for (User *GEPU : GEP->users())
408 if (LoadInst *LI = dyn_cast<LoadInst>(GEPU)) {
409 // Don't hack volatile/atomic loads
410 if (!LI->isSimple()) return false;
413 // Other uses than load?
417 return false; // Not a load or a GEP.
420 // Now, see if it is safe to promote this load / loads of this GEP. Loading
421 // is safe if Operands, or a prefix of Operands, is marked as safe.
422 if (!PrefixIn(Operands, SafeToUnconditionallyLoad))
425 // See if we are already promoting a load with these indices. If not, check
426 // to make sure that we aren't promoting too many elements. If so, nothing
428 if (ToPromote.find(Operands) == ToPromote.end()) {
429 if (maxElements > 0 && ToPromote.size() == maxElements) {
430 DEBUG(dbgs() << "argpromotion not promoting argument '"
431 << Arg->getName() << "' because it would require adding more "
432 << "than " << maxElements << " arguments to the function.\n");
433 // We limit aggregate promotion to only promoting up to a fixed number
434 // of elements of the aggregate.
437 ToPromote.insert(Operands);
441 if (Loads.empty()) return true; // No users, this is a dead argument.
443 // Okay, now we know that the argument is only used by load instructions and
444 // it is safe to unconditionally perform all of them. Use alias analysis to
445 // check to see if the pointer is guaranteed to not be modified from entry of
446 // the function to each of the load instructions.
448 // Because there could be several/many load instructions, remember which
449 // blocks we know to be transparent to the load.
450 SmallPtrSet<BasicBlock*, 16> TranspBlocks;
452 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
454 for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
455 // Check to see if the load is invalidated from the start of the block to
457 LoadInst *Load = Loads[i];
458 BasicBlock *BB = Load->getParent();
460 AliasAnalysis::Location Loc = AA.getLocation(Load);
461 if (AA.canInstructionRangeModify(BB->front(), *Load, Loc))
462 return false; // Pointer is invalidated!
464 // Now check every path from the entry block to the load for transparency.
465 // To do this, we perform a depth first search on the inverse CFG from the
467 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
469 for (idf_ext_iterator<BasicBlock*, SmallPtrSet<BasicBlock*, 16> >
470 I = idf_ext_begin(P, TranspBlocks),
471 E = idf_ext_end(P, TranspBlocks); I != E; ++I)
472 if (AA.canBasicBlockModify(**I, Loc))
477 // If the path from the entry of the function to each load is free of
478 // instructions that potentially invalidate the load, we can make the
483 /// DoPromotion - This method actually performs the promotion of the specified
484 /// arguments, and returns the new function. At this point, we know that it's
486 CallGraphNode *ArgPromotion::DoPromotion(Function *F,
487 SmallPtrSet<Argument*, 8> &ArgsToPromote,
488 SmallPtrSet<Argument*, 8> &ByValArgsToTransform) {
490 // Start by computing a new prototype for the function, which is the same as
491 // the old function, but has modified arguments.
492 FunctionType *FTy = F->getFunctionType();
493 std::vector<Type*> Params;
495 typedef std::set<IndicesVector> ScalarizeTable;
497 // ScalarizedElements - If we are promoting a pointer that has elements
498 // accessed out of it, keep track of which elements are accessed so that we
499 // can add one argument for each.
501 // Arguments that are directly loaded will have a zero element value here, to
502 // handle cases where there are both a direct load and GEP accesses.
504 std::map<Argument*, ScalarizeTable> ScalarizedElements;
506 // OriginalLoads - Keep track of a representative load instruction from the
507 // original function so that we can tell the alias analysis implementation
508 // what the new GEP/Load instructions we are inserting look like.
509 // We need to keep the original loads for each argument and the elements
510 // of the argument that are accessed.
511 std::map<std::pair<Argument*, IndicesVector>, LoadInst*> OriginalLoads;
513 // Attribute - Keep track of the parameter attributes for the arguments
514 // that we are *not* promoting. For the ones that we do promote, the parameter
515 // attributes are lost
516 SmallVector<AttributeSet, 8> AttributesVec;
517 const AttributeSet &PAL = F->getAttributes();
519 // Add any return attributes.
520 if (PAL.hasAttributes(AttributeSet::ReturnIndex))
521 AttributesVec.push_back(AttributeSet::get(F->getContext(),
522 PAL.getRetAttributes()));
524 // First, determine the new argument list
525 unsigned ArgIndex = 1;
526 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
528 if (ByValArgsToTransform.count(I)) {
529 // Simple byval argument? Just add all the struct element types.
530 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
531 StructType *STy = cast<StructType>(AgTy);
532 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i)
533 Params.push_back(STy->getElementType(i));
534 ++NumByValArgsPromoted;
535 } else if (!ArgsToPromote.count(I)) {
536 // Unchanged argument
537 Params.push_back(I->getType());
538 AttributeSet attrs = PAL.getParamAttributes(ArgIndex);
539 if (attrs.hasAttributes(ArgIndex)) {
540 AttrBuilder B(attrs, ArgIndex);
542 push_back(AttributeSet::get(F->getContext(), Params.size(), B));
544 } else if (I->use_empty()) {
545 // Dead argument (which are always marked as promotable)
548 // Okay, this is being promoted. This means that the only uses are loads
549 // or GEPs which are only used by loads
551 // In this table, we will track which indices are loaded from the argument
552 // (where direct loads are tracked as no indices).
553 ScalarizeTable &ArgIndices = ScalarizedElements[I];
554 for (User *U : I->users()) {
555 Instruction *UI = cast<Instruction>(U);
556 assert(isa<LoadInst>(UI) || isa<GetElementPtrInst>(UI));
557 IndicesVector Indices;
558 Indices.reserve(UI->getNumOperands() - 1);
559 // Since loads will only have a single operand, and GEPs only a single
560 // non-index operand, this will record direct loads without any indices,
561 // and gep+loads with the GEP indices.
562 for (User::op_iterator II = UI->op_begin() + 1, IE = UI->op_end();
564 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
565 // GEPs with a single 0 index can be merged with direct loads
566 if (Indices.size() == 1 && Indices.front() == 0)
568 ArgIndices.insert(Indices);
570 if (LoadInst *L = dyn_cast<LoadInst>(UI))
573 // Take any load, we will use it only to update Alias Analysis
574 OrigLoad = cast<LoadInst>(UI->user_back());
575 OriginalLoads[std::make_pair(I, Indices)] = OrigLoad;
578 // Add a parameter to the function for each element passed in.
579 for (ScalarizeTable::iterator SI = ArgIndices.begin(),
580 E = ArgIndices.end(); SI != E; ++SI) {
581 // not allowed to dereference ->begin() if size() is 0
582 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));
583 assert(Params.back());
586 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
587 ++NumArgumentsPromoted;
589 ++NumAggregatesPromoted;
593 // Add any function attributes.
594 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
595 AttributesVec.push_back(AttributeSet::get(FTy->getContext(),
596 PAL.getFnAttributes()));
598 Type *RetTy = FTy->getReturnType();
600 // Construct the new function type using the new arguments.
601 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
603 // Create the new function body and insert it into the module.
604 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
605 NF->copyAttributesFrom(F);
608 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n"
611 // Recompute the parameter attributes list based on the new arguments for
613 NF->setAttributes(AttributeSet::get(F->getContext(), AttributesVec));
614 AttributesVec.clear();
616 F->getParent()->getFunctionList().insert(F, NF);
619 // Get the alias analysis information that we need to update to reflect our
621 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
623 // Get the callgraph information that we need to update to reflect our
625 CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
627 // Get a new callgraph node for NF.
628 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF);
630 // Loop over all of the callers of the function, transforming the call sites
631 // to pass in the loaded pointers.
633 SmallVector<Value*, 16> Args;
634 while (!F->use_empty()) {
635 CallSite CS(F->user_back());
636 assert(CS.getCalledFunction() == F);
637 Instruction *Call = CS.getInstruction();
638 const AttributeSet &CallPAL = CS.getAttributes();
640 // Add any return attributes.
641 if (CallPAL.hasAttributes(AttributeSet::ReturnIndex))
642 AttributesVec.push_back(AttributeSet::get(F->getContext(),
643 CallPAL.getRetAttributes()));
645 // Loop over the operands, inserting GEP and loads in the caller as
647 CallSite::arg_iterator AI = CS.arg_begin();
649 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
650 I != E; ++I, ++AI, ++ArgIndex)
651 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
652 Args.push_back(*AI); // Unmodified argument
654 if (CallPAL.hasAttributes(ArgIndex)) {
655 AttrBuilder B(CallPAL, ArgIndex);
657 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
659 } else if (ByValArgsToTransform.count(I)) {
660 // Emit a GEP and load for each element of the struct.
661 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
662 StructType *STy = cast<StructType>(AgTy);
664 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr };
665 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
666 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
667 Value *Idx = GetElementPtrInst::Create(*AI, Idxs,
668 (*AI)->getName()+"."+utostr(i),
670 // TODO: Tell AA about the new values?
671 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call));
673 } else if (!I->use_empty()) {
674 // Non-dead argument: insert GEPs and loads as appropriate.
675 ScalarizeTable &ArgIndices = ScalarizedElements[I];
676 // Store the Value* version of the indices in here, but declare it now
678 std::vector<Value*> Ops;
679 for (ScalarizeTable::iterator SI = ArgIndices.begin(),
680 E = ArgIndices.end(); SI != E; ++SI) {
682 LoadInst *OrigLoad = OriginalLoads[std::make_pair(I, *SI)];
684 Ops.reserve(SI->size());
685 Type *ElTy = V->getType();
686 for (IndicesVector::const_iterator II = SI->begin(),
687 IE = SI->end(); II != IE; ++II) {
688 // Use i32 to index structs, and i64 for others (pointers/arrays).
689 // This satisfies GEP constraints.
690 Type *IdxTy = (ElTy->isStructTy() ?
691 Type::getInt32Ty(F->getContext()) :
692 Type::getInt64Ty(F->getContext()));
693 Ops.push_back(ConstantInt::get(IdxTy, *II));
694 // Keep track of the type we're currently indexing.
695 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II);
697 // And create a GEP to extract those indices.
698 V = GetElementPtrInst::Create(V, Ops, V->getName()+".idx", Call);
700 AA.copyValue(OrigLoad->getOperand(0), V);
702 // Since we're replacing a load make sure we take the alignment
703 // of the previous load.
704 LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call);
705 newLoad->setAlignment(OrigLoad->getAlignment());
706 // Transfer the TBAA info too.
707 newLoad->setMetadata(LLVMContext::MD_tbaa,
708 OrigLoad->getMetadata(LLVMContext::MD_tbaa));
709 Args.push_back(newLoad);
710 AA.copyValue(OrigLoad, Args.back());
714 // Push any varargs arguments on the list.
715 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) {
717 if (CallPAL.hasAttributes(ArgIndex)) {
718 AttrBuilder B(CallPAL, ArgIndex);
720 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
724 // Add any function attributes.
725 if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
726 AttributesVec.push_back(AttributeSet::get(Call->getContext(),
727 CallPAL.getFnAttributes()));
730 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
731 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
733 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
734 cast<InvokeInst>(New)->setAttributes(AttributeSet::get(II->getContext(),
737 New = CallInst::Create(NF, Args, "", Call);
738 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
739 cast<CallInst>(New)->setAttributes(AttributeSet::get(New->getContext(),
741 if (cast<CallInst>(Call)->isTailCall())
742 cast<CallInst>(New)->setTailCall();
745 AttributesVec.clear();
747 // Update the alias analysis implementation to know that we are replacing
748 // the old call with a new one.
749 AA.replaceWithNewValue(Call, New);
751 // Update the callgraph to know that the callsite has been transformed.
752 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()];
753 CalleeNode->replaceCallEdge(Call, New, NF_CGN);
755 if (!Call->use_empty()) {
756 Call->replaceAllUsesWith(New);
760 // Finally, remove the old call from the program, reducing the use-count of
762 Call->eraseFromParent();
765 // Since we have now created the new function, splice the body of the old
766 // function right into the new function, leaving the old rotting hulk of the
768 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
770 // Loop over the argument list, transferring uses of the old arguments over to
771 // the new arguments, also transferring over the names as well.
773 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
774 I2 = NF->arg_begin(); I != E; ++I) {
775 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
776 // If this is an unmodified argument, move the name and users over to the
778 I->replaceAllUsesWith(I2);
780 AA.replaceWithNewValue(I, I2);
785 if (ByValArgsToTransform.count(I)) {
786 // In the callee, we create an alloca, and store each of the new incoming
787 // arguments into the alloca.
788 Instruction *InsertPt = NF->begin()->begin();
790 // Just add all the struct element types.
791 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
792 Value *TheAlloca = new AllocaInst(AgTy, nullptr, "", InsertPt);
793 StructType *STy = cast<StructType>(AgTy);
795 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr };
797 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
798 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
800 GetElementPtrInst::Create(TheAlloca, Idxs,
801 TheAlloca->getName()+"."+Twine(i),
803 I2->setName(I->getName()+"."+Twine(i));
804 new StoreInst(I2++, Idx, InsertPt);
807 // Anything that used the arg should now use the alloca.
808 I->replaceAllUsesWith(TheAlloca);
809 TheAlloca->takeName(I);
810 AA.replaceWithNewValue(I, TheAlloca);
812 // If the alloca is used in a call, we must clear the tail flag since
813 // the callee now uses an alloca from the caller.
814 for (User *U : TheAlloca->users()) {
815 CallInst *Call = dyn_cast<CallInst>(U);
818 Call->setTailCall(false);
823 if (I->use_empty()) {
828 // Otherwise, if we promoted this argument, then all users are load
829 // instructions (or GEPs with only load users), and all loads should be
830 // using the new argument that we added.
831 ScalarizeTable &ArgIndices = ScalarizedElements[I];
833 while (!I->use_empty()) {
834 if (LoadInst *LI = dyn_cast<LoadInst>(I->user_back())) {
835 assert(ArgIndices.begin()->empty() &&
836 "Load element should sort to front!");
837 I2->setName(I->getName()+".val");
838 LI->replaceAllUsesWith(I2);
839 AA.replaceWithNewValue(LI, I2);
840 LI->eraseFromParent();
841 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName()
842 << "' in function '" << F->getName() << "'\n");
844 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->user_back());
845 IndicesVector Operands;
846 Operands.reserve(GEP->getNumIndices());
847 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
849 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
851 // GEPs with a single 0 index can be merged with direct loads
852 if (Operands.size() == 1 && Operands.front() == 0)
855 Function::arg_iterator TheArg = I2;
856 for (ScalarizeTable::iterator It = ArgIndices.begin();
857 *It != Operands; ++It, ++TheArg) {
858 assert(It != ArgIndices.end() && "GEP not handled??");
861 std::string NewName = I->getName();
862 for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
863 NewName += "." + utostr(Operands[i]);
866 TheArg->setName(NewName);
868 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName()
869 << "' of function '" << NF->getName() << "'\n");
871 // All of the uses must be load instructions. Replace them all with
872 // the argument specified by ArgNo.
873 while (!GEP->use_empty()) {
874 LoadInst *L = cast<LoadInst>(GEP->user_back());
875 L->replaceAllUsesWith(TheArg);
876 AA.replaceWithNewValue(L, TheArg);
877 L->eraseFromParent();
880 GEP->eraseFromParent();
884 // Increment I2 past all of the arguments added for this promoted pointer.
885 std::advance(I2, ArgIndices.size());
888 // Tell the alias analysis that the old function is about to disappear.
889 AA.replaceWithNewValue(F, NF);
892 NF_CGN->stealCalledFunctionsFrom(CG[F]);
894 // Now that the old function is dead, delete it. If there is a dangling
895 // reference to the CallgraphNode, just leave the dead function around for
896 // someone else to nuke.
897 CallGraphNode *CGN = CG[F];
898 if (CGN->getNumReferences() == 0)
899 delete CG.removeFunctionFromModule(CGN);
901 F->setLinkage(Function::ExternalLinkage);