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/DataLayout.h"
43 #include "llvm/IR/DebugInfo.h"
44 #include "llvm/IR/DerivedTypes.h"
45 #include "llvm/IR/Instructions.h"
46 #include "llvm/IR/LLVMContext.h"
47 #include "llvm/IR/Module.h"
48 #include "llvm/Support/Debug.h"
49 #include "llvm/Support/raw_ostream.h"
53 #define DEBUG_TYPE "argpromotion"
55 STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted");
56 STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
57 STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted");
58 STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated");
61 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
63 struct ArgPromotion : public CallGraphSCCPass {
64 void getAnalysisUsage(AnalysisUsage &AU) const override {
65 AU.addRequired<AliasAnalysis>();
66 CallGraphSCCPass::getAnalysisUsage(AU);
69 bool runOnSCC(CallGraphSCC &SCC) override;
70 static char ID; // Pass identification, replacement for typeid
71 explicit ArgPromotion(unsigned maxElements = 3)
72 : CallGraphSCCPass(ID), DL(nullptr), maxElements(maxElements) {
73 initializeArgPromotionPass(*PassRegistry::getPassRegistry());
76 /// A vector used to hold the indices of a single GEP instruction
77 typedef std::vector<uint64_t> IndicesVector;
81 bool isDenselyPacked(Type *type);
82 bool canPaddingBeAccessed(Argument *Arg);
83 CallGraphNode *PromoteArguments(CallGraphNode *CGN);
84 bool isSafeToPromoteArgument(Argument *Arg, bool isByVal) const;
85 CallGraphNode *DoPromotion(Function *F,
86 SmallPtrSetImpl<Argument*> &ArgsToPromote,
87 SmallPtrSetImpl<Argument*> &ByValArgsToTransform);
89 using llvm::Pass::doInitialization;
90 bool doInitialization(CallGraph &CG) override;
91 /// The maximum number of elements to expand, or 0 for unlimited.
93 DenseMap<const Function *, DISubprogram> FunctionDIs;
97 char ArgPromotion::ID = 0;
98 INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion",
99 "Promote 'by reference' arguments to scalars", false, false)
100 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
101 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
102 INITIALIZE_PASS_END(ArgPromotion, "argpromotion",
103 "Promote 'by reference' arguments to scalars", false, false)
105 Pass *llvm::createArgumentPromotionPass(unsigned maxElements) {
106 return new ArgPromotion(maxElements);
109 bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) {
110 bool Changed = false, LocalChange;
112 do { // Iterate until we stop promoting from this SCC.
114 // Attempt to promote arguments from all functions in this SCC.
115 for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
116 if (CallGraphNode *CGN = PromoteArguments(*I)) {
118 SCC.ReplaceNode(*I, CGN);
121 Changed |= LocalChange; // Remember that we changed something.
122 } while (LocalChange);
127 /// \brief Checks if a type could have padding bytes.
128 bool ArgPromotion::isDenselyPacked(Type *type) {
130 // There is no size information, so be conservative.
131 if (!type->isSized())
134 // If the alloc size is not equal to the storage size, then there are padding
135 // bytes. For x86_fp80 on x86-64, size: 80 alloc size: 128.
136 if (!DL || DL->getTypeSizeInBits(type) != DL->getTypeAllocSizeInBits(type))
139 if (!isa<CompositeType>(type))
142 // For homogenous sequential types, check for padding within members.
143 if (SequentialType *seqTy = dyn_cast<SequentialType>(type))
144 return isa<PointerType>(seqTy) || isDenselyPacked(seqTy->getElementType());
146 // Check for padding within and between elements of a struct.
147 StructType *StructTy = cast<StructType>(type);
148 const StructLayout *Layout = DL->getStructLayout(StructTy);
149 uint64_t StartPos = 0;
150 for (unsigned i = 0, E = StructTy->getNumElements(); i < E; ++i) {
151 Type *ElTy = StructTy->getElementType(i);
152 if (!isDenselyPacked(ElTy))
154 if (StartPos != Layout->getElementOffsetInBits(i))
156 StartPos += DL->getTypeAllocSizeInBits(ElTy);
162 /// \brief Checks if the padding bytes of an argument could be accessed.
163 bool ArgPromotion::canPaddingBeAccessed(Argument *arg) {
165 assert(arg->hasByValAttr());
167 // Track all the pointers to the argument to make sure they are not captured.
168 SmallPtrSet<Value *, 16> PtrValues;
169 PtrValues.insert(arg);
171 // Track all of the stores.
172 SmallVector<StoreInst *, 16> Stores;
174 // Scan through the uses recursively to make sure the pointer is always used
176 SmallVector<Value *, 16> WorkList;
177 WorkList.insert(WorkList.end(), arg->user_begin(), arg->user_end());
178 while (!WorkList.empty()) {
179 Value *V = WorkList.back();
181 if (isa<GetElementPtrInst>(V) || isa<PHINode>(V)) {
182 if (PtrValues.insert(V).second)
183 WorkList.insert(WorkList.end(), V->user_begin(), V->user_end());
184 } else if (StoreInst *Store = dyn_cast<StoreInst>(V)) {
185 Stores.push_back(Store);
186 } else if (!isa<LoadInst>(V)) {
191 // Check to make sure the pointers aren't captured
192 for (StoreInst *Store : Stores)
193 if (PtrValues.count(Store->getValueOperand()))
199 /// PromoteArguments - This method checks the specified function to see if there
200 /// are any promotable arguments and if it is safe to promote the function (for
201 /// example, all callers are direct). If safe to promote some arguments, it
202 /// calls the DoPromotion method.
204 CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
205 Function *F = CGN->getFunction();
207 // Make sure that it is local to this module.
208 if (!F || !F->hasLocalLinkage()) return nullptr;
210 DL = &F->getParent()->getDataLayout();
212 // First check: see if there are any pointer arguments! If not, quick exit.
213 SmallVector<Argument*, 16> PointerArgs;
214 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
215 if (I->getType()->isPointerTy())
216 PointerArgs.push_back(I);
217 if (PointerArgs.empty()) return nullptr;
219 // Second check: make sure that all callers are direct callers. We can't
220 // transform functions that have indirect callers. Also see if the function
221 // is self-recursive.
222 bool isSelfRecursive = false;
223 for (Use &U : F->uses()) {
224 CallSite CS(U.getUser());
225 // Must be a direct call.
226 if (CS.getInstruction() == nullptr || !CS.isCallee(&U)) return nullptr;
228 if (CS.getInstruction()->getParent()->getParent() == F)
229 isSelfRecursive = true;
232 // Don't promote arguments for variadic functions. Adding, removing, or
233 // changing non-pack parameters can change the classification of pack
234 // parameters. Frontends encode that classification at the call site in the
235 // IR, while in the callee the classification is determined dynamically based
236 // on the number of registers consumed so far.
237 if (F->isVarArg()) return nullptr;
239 // Check to see which arguments are promotable. If an argument is promotable,
240 // add it to ArgsToPromote.
241 SmallPtrSet<Argument*, 8> ArgsToPromote;
242 SmallPtrSet<Argument*, 8> ByValArgsToTransform;
243 for (unsigned i = 0, e = PointerArgs.size(); i != e; ++i) {
244 Argument *PtrArg = PointerArgs[i];
245 Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
247 // If this is a byval argument, and if the aggregate type is small, just
248 // pass the elements, which is always safe, if the passed value is densely
249 // packed or if we can prove the padding bytes are never accessed. This does
250 // not apply to inalloca.
251 bool isSafeToPromote =
252 PtrArg->hasByValAttr() &&
253 (isDenselyPacked(AgTy) || !canPaddingBeAccessed(PtrArg));
254 if (isSafeToPromote) {
255 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
256 if (maxElements > 0 && STy->getNumElements() > maxElements) {
257 DEBUG(dbgs() << "argpromotion disable promoting argument '"
258 << PtrArg->getName() << "' because it would require adding more"
259 << " than " << maxElements << " arguments to the function.\n");
263 // If all the elements are single-value types, we can promote it.
264 bool AllSimple = true;
265 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
266 if (!STy->getElementType(i)->isSingleValueType()) {
272 // Safe to transform, don't even bother trying to "promote" it.
273 // Passing the elements as a scalar will allow scalarrepl to hack on
274 // the new alloca we introduce.
276 ByValArgsToTransform.insert(PtrArg);
282 // If the argument is a recursive type and we're in a recursive
283 // function, we could end up infinitely peeling the function argument.
284 if (isSelfRecursive) {
285 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
286 bool RecursiveType = false;
287 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
288 if (STy->getElementType(i) == PtrArg->getType()) {
289 RecursiveType = true;
298 // Otherwise, see if we can promote the pointer to its value.
299 if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValOrInAllocaAttr()))
300 ArgsToPromote.insert(PtrArg);
303 // No promotable pointer arguments.
304 if (ArgsToPromote.empty() && ByValArgsToTransform.empty())
307 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform);
310 /// AllCallersPassInValidPointerForArgument - Return true if we can prove that
311 /// all callees pass in a valid pointer for the specified function argument.
312 static bool AllCallersPassInValidPointerForArgument(Argument *Arg,
313 const DataLayout *DL) {
314 Function *Callee = Arg->getParent();
316 unsigned ArgNo = Arg->getArgNo();
318 // Look at all call sites of the function. At this pointer we know we only
319 // have direct callees.
320 for (User *U : Callee->users()) {
322 assert(CS && "Should only have direct calls!");
324 if (!CS.getArgument(ArgNo)->isDereferenceablePointer(DL))
330 /// Returns true if Prefix is a prefix of longer. That means, Longer has a size
331 /// that is greater than or equal to the size of prefix, and each of the
332 /// elements in Prefix is the same as the corresponding elements in Longer.
334 /// This means it also returns true when Prefix and Longer are equal!
335 static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix,
336 const ArgPromotion::IndicesVector &Longer) {
337 if (Prefix.size() > Longer.size())
339 return std::equal(Prefix.begin(), Prefix.end(), Longer.begin());
343 /// Checks if Indices, or a prefix of Indices, is in Set.
344 static bool PrefixIn(const ArgPromotion::IndicesVector &Indices,
345 std::set<ArgPromotion::IndicesVector> &Set) {
346 std::set<ArgPromotion::IndicesVector>::iterator Low;
347 Low = Set.upper_bound(Indices);
348 if (Low != Set.begin())
350 // Low is now the last element smaller than or equal to Indices. This means
351 // it points to a prefix of Indices (possibly Indices itself), if such
354 // This load is safe if any prefix of its operands is safe to load.
355 return Low != Set.end() && IsPrefix(*Low, Indices);
358 /// Mark the given indices (ToMark) as safe in the given set of indices
359 /// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
360 /// is already a prefix of Indices in Safe, Indices are implicitely marked safe
361 /// already. Furthermore, any indices that Indices is itself a prefix of, are
362 /// removed from Safe (since they are implicitely safe because of Indices now).
363 static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark,
364 std::set<ArgPromotion::IndicesVector> &Safe) {
365 std::set<ArgPromotion::IndicesVector>::iterator Low;
366 Low = Safe.upper_bound(ToMark);
367 // Guard against the case where Safe is empty
368 if (Low != Safe.begin())
370 // Low is now the last element smaller than or equal to Indices. This
371 // means it points to a prefix of Indices (possibly Indices itself), if
372 // such prefix exists.
373 if (Low != Safe.end()) {
374 if (IsPrefix(*Low, ToMark))
375 // If there is already a prefix of these indices (or exactly these
376 // indices) marked a safe, don't bother adding these indices
379 // Increment Low, so we can use it as a "insert before" hint
383 Low = Safe.insert(Low, ToMark);
385 // If there we're a prefix of longer index list(s), remove those
386 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end();
387 while (Low != End && IsPrefix(ToMark, *Low)) {
388 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low;
394 /// isSafeToPromoteArgument - As you might guess from the name of this method,
395 /// it checks to see if it is both safe and useful to promote the argument.
396 /// This method limits promotion of aggregates to only promote up to three
397 /// elements of the aggregate in order to avoid exploding the number of
398 /// arguments passed in.
399 bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg,
400 bool isByValOrInAlloca) const {
401 typedef std::set<IndicesVector> GEPIndicesSet;
403 // Quick exit for unused arguments
404 if (Arg->use_empty())
407 // We can only promote this argument if all of the uses are loads, or are GEP
408 // instructions (with constant indices) that are subsequently loaded.
410 // Promoting the argument causes it to be loaded in the caller
411 // unconditionally. This is only safe if we can prove that either the load
412 // would have happened in the callee anyway (ie, there is a load in the entry
413 // block) or the pointer passed in at every call site is guaranteed to be
415 // In the former case, invalid loads can happen, but would have happened
416 // anyway, in the latter case, invalid loads won't happen. This prevents us
417 // from introducing an invalid load that wouldn't have happened in the
420 // This set will contain all sets of indices that are loaded in the entry
421 // block, and thus are safe to unconditionally load in the caller.
423 // This optimization is also safe for InAlloca parameters, because it verifies
424 // that the address isn't captured.
425 GEPIndicesSet SafeToUnconditionallyLoad;
427 // This set contains all the sets of indices that we are planning to promote.
428 // This makes it possible to limit the number of arguments added.
429 GEPIndicesSet ToPromote;
431 // If the pointer is always valid, any load with first index 0 is valid.
432 if (isByValOrInAlloca || AllCallersPassInValidPointerForArgument(Arg, DL))
433 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
435 // First, iterate the entry block and mark loads of (geps of) arguments as
437 BasicBlock *EntryBlock = Arg->getParent()->begin();
438 // Declare this here so we can reuse it
439 IndicesVector Indices;
440 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end();
442 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
443 Value *V = LI->getPointerOperand();
444 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
445 V = GEP->getPointerOperand();
447 // This load actually loads (part of) Arg? Check the indices then.
448 Indices.reserve(GEP->getNumIndices());
449 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
451 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
452 Indices.push_back(CI->getSExtValue());
454 // We found a non-constant GEP index for this argument? Bail out
455 // right away, can't promote this argument at all.
458 // Indices checked out, mark them as safe
459 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad);
462 } else if (V == Arg) {
463 // Direct loads are equivalent to a GEP with a single 0 index.
464 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
468 // Now, iterate all uses of the argument to see if there are any uses that are
469 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
470 SmallVector<LoadInst*, 16> Loads;
471 IndicesVector Operands;
472 for (Use &U : Arg->uses()) {
473 User *UR = U.getUser();
475 if (LoadInst *LI = dyn_cast<LoadInst>(UR)) {
476 // Don't hack volatile/atomic loads
477 if (!LI->isSimple()) return false;
479 // Direct loads are equivalent to a GEP with a zero index and then a load.
480 Operands.push_back(0);
481 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UR)) {
482 if (GEP->use_empty()) {
483 // Dead GEP's cause trouble later. Just remove them if we run into
485 getAnalysis<AliasAnalysis>().deleteValue(GEP);
486 GEP->eraseFromParent();
487 // TODO: This runs the above loop over and over again for dead GEPs
488 // Couldn't we just do increment the UI iterator earlier and erase the
490 return isSafeToPromoteArgument(Arg, isByValOrInAlloca);
493 // Ensure that all of the indices are constants.
494 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end();
496 if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
497 Operands.push_back(C->getSExtValue());
499 return false; // Not a constant operand GEP!
501 // Ensure that the only users of the GEP are load instructions.
502 for (User *GEPU : GEP->users())
503 if (LoadInst *LI = dyn_cast<LoadInst>(GEPU)) {
504 // Don't hack volatile/atomic loads
505 if (!LI->isSimple()) return false;
508 // Other uses than load?
512 return false; // Not a load or a GEP.
515 // Now, see if it is safe to promote this load / loads of this GEP. Loading
516 // is safe if Operands, or a prefix of Operands, is marked as safe.
517 if (!PrefixIn(Operands, SafeToUnconditionallyLoad))
520 // See if we are already promoting a load with these indices. If not, check
521 // to make sure that we aren't promoting too many elements. If so, nothing
523 if (ToPromote.find(Operands) == ToPromote.end()) {
524 if (maxElements > 0 && ToPromote.size() == maxElements) {
525 DEBUG(dbgs() << "argpromotion not promoting argument '"
526 << Arg->getName() << "' because it would require adding more "
527 << "than " << maxElements << " arguments to the function.\n");
528 // We limit aggregate promotion to only promoting up to a fixed number
529 // of elements of the aggregate.
532 ToPromote.insert(std::move(Operands));
536 if (Loads.empty()) return true; // No users, this is a dead argument.
538 // Okay, now we know that the argument is only used by load instructions and
539 // it is safe to unconditionally perform all of them. Use alias analysis to
540 // check to see if the pointer is guaranteed to not be modified from entry of
541 // the function to each of the load instructions.
543 // Because there could be several/many load instructions, remember which
544 // blocks we know to be transparent to the load.
545 SmallPtrSet<BasicBlock*, 16> TranspBlocks;
547 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
549 for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
550 // Check to see if the load is invalidated from the start of the block to
552 LoadInst *Load = Loads[i];
553 BasicBlock *BB = Load->getParent();
555 AliasAnalysis::Location Loc = AA.getLocation(Load);
556 if (AA.canInstructionRangeModRef(BB->front(), *Load, Loc,
558 return false; // Pointer is invalidated!
560 // Now check every path from the entry block to the load for transparency.
561 // To do this, we perform a depth first search on the inverse CFG from the
563 for (BasicBlock *P : predecessors(BB)) {
564 for (BasicBlock *TranspBB : inverse_depth_first_ext(P, TranspBlocks))
565 if (AA.canBasicBlockModify(*TranspBB, Loc))
570 // If the path from the entry of the function to each load is free of
571 // instructions that potentially invalidate the load, we can make the
576 /// DoPromotion - This method actually performs the promotion of the specified
577 /// arguments, and returns the new function. At this point, we know that it's
579 CallGraphNode *ArgPromotion::DoPromotion(Function *F,
580 SmallPtrSetImpl<Argument*> &ArgsToPromote,
581 SmallPtrSetImpl<Argument*> &ByValArgsToTransform) {
583 // Start by computing a new prototype for the function, which is the same as
584 // the old function, but has modified arguments.
585 FunctionType *FTy = F->getFunctionType();
586 std::vector<Type*> Params;
588 typedef std::set<IndicesVector> ScalarizeTable;
590 // ScalarizedElements - If we are promoting a pointer that has elements
591 // accessed out of it, keep track of which elements are accessed so that we
592 // can add one argument for each.
594 // Arguments that are directly loaded will have a zero element value here, to
595 // handle cases where there are both a direct load and GEP accesses.
597 std::map<Argument*, ScalarizeTable> ScalarizedElements;
599 // OriginalLoads - Keep track of a representative load instruction from the
600 // original function so that we can tell the alias analysis implementation
601 // what the new GEP/Load instructions we are inserting look like.
602 // We need to keep the original loads for each argument and the elements
603 // of the argument that are accessed.
604 std::map<std::pair<Argument*, IndicesVector>, LoadInst*> OriginalLoads;
606 // Attribute - Keep track of the parameter attributes for the arguments
607 // that we are *not* promoting. For the ones that we do promote, the parameter
608 // attributes are lost
609 SmallVector<AttributeSet, 8> AttributesVec;
610 const AttributeSet &PAL = F->getAttributes();
612 // Add any return attributes.
613 if (PAL.hasAttributes(AttributeSet::ReturnIndex))
614 AttributesVec.push_back(AttributeSet::get(F->getContext(),
615 PAL.getRetAttributes()));
617 // First, determine the new argument list
618 unsigned ArgIndex = 1;
619 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
621 if (ByValArgsToTransform.count(I)) {
622 // Simple byval argument? Just add all the struct element types.
623 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
624 StructType *STy = cast<StructType>(AgTy);
625 Params.insert(Params.end(), STy->element_begin(), STy->element_end());
626 ++NumByValArgsPromoted;
627 } else if (!ArgsToPromote.count(I)) {
628 // Unchanged argument
629 Params.push_back(I->getType());
630 AttributeSet attrs = PAL.getParamAttributes(ArgIndex);
631 if (attrs.hasAttributes(ArgIndex)) {
632 AttrBuilder B(attrs, ArgIndex);
634 push_back(AttributeSet::get(F->getContext(), Params.size(), B));
636 } else if (I->use_empty()) {
637 // Dead argument (which are always marked as promotable)
640 // Okay, this is being promoted. This means that the only uses are loads
641 // or GEPs which are only used by loads
643 // In this table, we will track which indices are loaded from the argument
644 // (where direct loads are tracked as no indices).
645 ScalarizeTable &ArgIndices = ScalarizedElements[I];
646 for (User *U : I->users()) {
647 Instruction *UI = cast<Instruction>(U);
648 assert(isa<LoadInst>(UI) || isa<GetElementPtrInst>(UI));
649 IndicesVector Indices;
650 Indices.reserve(UI->getNumOperands() - 1);
651 // Since loads will only have a single operand, and GEPs only a single
652 // non-index operand, this will record direct loads without any indices,
653 // and gep+loads with the GEP indices.
654 for (User::op_iterator II = UI->op_begin() + 1, IE = UI->op_end();
656 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
657 // GEPs with a single 0 index can be merged with direct loads
658 if (Indices.size() == 1 && Indices.front() == 0)
660 ArgIndices.insert(Indices);
662 if (LoadInst *L = dyn_cast<LoadInst>(UI))
665 // Take any load, we will use it only to update Alias Analysis
666 OrigLoad = cast<LoadInst>(UI->user_back());
667 OriginalLoads[std::make_pair(I, Indices)] = OrigLoad;
670 // Add a parameter to the function for each element passed in.
671 for (ScalarizeTable::iterator SI = ArgIndices.begin(),
672 E = ArgIndices.end(); SI != E; ++SI) {
673 // not allowed to dereference ->begin() if size() is 0
674 Params.push_back(GetElementPtrInst::getIndexedType(I->getType(), *SI));
675 assert(Params.back());
678 if (ArgIndices.size() == 1 && ArgIndices.begin()->empty())
679 ++NumArgumentsPromoted;
681 ++NumAggregatesPromoted;
685 // Add any function attributes.
686 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
687 AttributesVec.push_back(AttributeSet::get(FTy->getContext(),
688 PAL.getFnAttributes()));
690 Type *RetTy = FTy->getReturnType();
692 // Construct the new function type using the new arguments.
693 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
695 // Create the new function body and insert it into the module.
696 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
697 NF->copyAttributesFrom(F);
699 // Patch the pointer to LLVM function in debug info descriptor.
700 auto DI = FunctionDIs.find(F);
701 if (DI != FunctionDIs.end()) {
702 DISubprogram SP = DI->second;
703 SP.replaceFunction(NF);
704 // Ensure the map is updated so it can be reused on subsequent argument
705 // promotions of the same function.
706 FunctionDIs.erase(DI);
707 FunctionDIs[NF] = SP;
710 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n"
713 // Recompute the parameter attributes list based on the new arguments for
715 NF->setAttributes(AttributeSet::get(F->getContext(), AttributesVec));
716 AttributesVec.clear();
718 F->getParent()->getFunctionList().insert(F, NF);
721 // Get the alias analysis information that we need to update to reflect our
723 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
725 // Get the callgraph information that we need to update to reflect our
727 CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
729 // Get a new callgraph node for NF.
730 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF);
732 // Loop over all of the callers of the function, transforming the call sites
733 // to pass in the loaded pointers.
735 SmallVector<Value*, 16> Args;
736 while (!F->use_empty()) {
737 CallSite CS(F->user_back());
738 assert(CS.getCalledFunction() == F);
739 Instruction *Call = CS.getInstruction();
740 const AttributeSet &CallPAL = CS.getAttributes();
742 // Add any return attributes.
743 if (CallPAL.hasAttributes(AttributeSet::ReturnIndex))
744 AttributesVec.push_back(AttributeSet::get(F->getContext(),
745 CallPAL.getRetAttributes()));
747 // Loop over the operands, inserting GEP and loads in the caller as
749 CallSite::arg_iterator AI = CS.arg_begin();
751 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
752 I != E; ++I, ++AI, ++ArgIndex)
753 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
754 Args.push_back(*AI); // Unmodified argument
756 if (CallPAL.hasAttributes(ArgIndex)) {
757 AttrBuilder B(CallPAL, ArgIndex);
759 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
761 } else if (ByValArgsToTransform.count(I)) {
762 // Emit a GEP and load for each element of the struct.
763 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
764 StructType *STy = cast<StructType>(AgTy);
766 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr };
767 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
768 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
769 Value *Idx = GetElementPtrInst::Create(*AI, Idxs,
770 (*AI)->getName()+"."+utostr(i),
772 // TODO: Tell AA about the new values?
773 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call));
775 } else if (!I->use_empty()) {
776 // Non-dead argument: insert GEPs and loads as appropriate.
777 ScalarizeTable &ArgIndices = ScalarizedElements[I];
778 // Store the Value* version of the indices in here, but declare it now
780 std::vector<Value*> Ops;
781 for (ScalarizeTable::iterator SI = ArgIndices.begin(),
782 E = ArgIndices.end(); SI != E; ++SI) {
784 LoadInst *OrigLoad = OriginalLoads[std::make_pair(I, *SI)];
786 Ops.reserve(SI->size());
787 Type *ElTy = V->getType();
788 for (IndicesVector::const_iterator II = SI->begin(),
789 IE = SI->end(); II != IE; ++II) {
790 // Use i32 to index structs, and i64 for others (pointers/arrays).
791 // This satisfies GEP constraints.
792 Type *IdxTy = (ElTy->isStructTy() ?
793 Type::getInt32Ty(F->getContext()) :
794 Type::getInt64Ty(F->getContext()));
795 Ops.push_back(ConstantInt::get(IdxTy, *II));
796 // Keep track of the type we're currently indexing.
797 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II);
799 // And create a GEP to extract those indices.
800 V = GetElementPtrInst::Create(V, Ops, V->getName()+".idx", Call);
802 AA.copyValue(OrigLoad->getOperand(0), V);
804 // Since we're replacing a load make sure we take the alignment
805 // of the previous load.
806 LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call);
807 newLoad->setAlignment(OrigLoad->getAlignment());
808 // Transfer the AA info too.
810 OrigLoad->getAAMetadata(AAInfo);
811 newLoad->setAAMetadata(AAInfo);
813 Args.push_back(newLoad);
814 AA.copyValue(OrigLoad, Args.back());
818 // Push any varargs arguments on the list.
819 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) {
821 if (CallPAL.hasAttributes(ArgIndex)) {
822 AttrBuilder B(CallPAL, ArgIndex);
824 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
828 // Add any function attributes.
829 if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
830 AttributesVec.push_back(AttributeSet::get(Call->getContext(),
831 CallPAL.getFnAttributes()));
834 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
835 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
837 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
838 cast<InvokeInst>(New)->setAttributes(AttributeSet::get(II->getContext(),
841 New = CallInst::Create(NF, Args, "", Call);
842 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
843 cast<CallInst>(New)->setAttributes(AttributeSet::get(New->getContext(),
845 if (cast<CallInst>(Call)->isTailCall())
846 cast<CallInst>(New)->setTailCall();
848 New->setDebugLoc(Call->getDebugLoc());
850 AttributesVec.clear();
852 // Update the alias analysis implementation to know that we are replacing
853 // the old call with a new one.
854 AA.replaceWithNewValue(Call, New);
856 // Update the callgraph to know that the callsite has been transformed.
857 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()];
858 CalleeNode->replaceCallEdge(Call, New, NF_CGN);
860 if (!Call->use_empty()) {
861 Call->replaceAllUsesWith(New);
865 // Finally, remove the old call from the program, reducing the use-count of
867 Call->eraseFromParent();
870 // Since we have now created the new function, splice the body of the old
871 // function right into the new function, leaving the old rotting hulk of the
873 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
875 // Loop over the argument list, transferring uses of the old arguments over to
876 // the new arguments, also transferring over the names as well.
878 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
879 I2 = NF->arg_begin(); I != E; ++I) {
880 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
881 // If this is an unmodified argument, move the name and users over to the
883 I->replaceAllUsesWith(I2);
885 AA.replaceWithNewValue(I, I2);
890 if (ByValArgsToTransform.count(I)) {
891 // In the callee, we create an alloca, and store each of the new incoming
892 // arguments into the alloca.
893 Instruction *InsertPt = NF->begin()->begin();
895 // Just add all the struct element types.
896 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
897 Value *TheAlloca = new AllocaInst(AgTy, nullptr, "", InsertPt);
898 StructType *STy = cast<StructType>(AgTy);
900 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr };
902 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
903 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
905 GetElementPtrInst::Create(TheAlloca, Idxs,
906 TheAlloca->getName()+"."+Twine(i),
908 I2->setName(I->getName()+"."+Twine(i));
909 new StoreInst(I2++, Idx, InsertPt);
912 // Anything that used the arg should now use the alloca.
913 I->replaceAllUsesWith(TheAlloca);
914 TheAlloca->takeName(I);
915 AA.replaceWithNewValue(I, TheAlloca);
917 // If the alloca is used in a call, we must clear the tail flag since
918 // the callee now uses an alloca from the caller.
919 for (User *U : TheAlloca->users()) {
920 CallInst *Call = dyn_cast<CallInst>(U);
923 Call->setTailCall(false);
928 if (I->use_empty()) {
933 // Otherwise, if we promoted this argument, then all users are load
934 // instructions (or GEPs with only load users), and all loads should be
935 // using the new argument that we added.
936 ScalarizeTable &ArgIndices = ScalarizedElements[I];
938 while (!I->use_empty()) {
939 if (LoadInst *LI = dyn_cast<LoadInst>(I->user_back())) {
940 assert(ArgIndices.begin()->empty() &&
941 "Load element should sort to front!");
942 I2->setName(I->getName()+".val");
943 LI->replaceAllUsesWith(I2);
944 AA.replaceWithNewValue(LI, I2);
945 LI->eraseFromParent();
946 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName()
947 << "' in function '" << F->getName() << "'\n");
949 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->user_back());
950 IndicesVector Operands;
951 Operands.reserve(GEP->getNumIndices());
952 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
954 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
956 // GEPs with a single 0 index can be merged with direct loads
957 if (Operands.size() == 1 && Operands.front() == 0)
960 Function::arg_iterator TheArg = I2;
961 for (ScalarizeTable::iterator It = ArgIndices.begin();
962 *It != Operands; ++It, ++TheArg) {
963 assert(It != ArgIndices.end() && "GEP not handled??");
966 std::string NewName = I->getName();
967 for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
968 NewName += "." + utostr(Operands[i]);
971 TheArg->setName(NewName);
973 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName()
974 << "' of function '" << NF->getName() << "'\n");
976 // All of the uses must be load instructions. Replace them all with
977 // the argument specified by ArgNo.
978 while (!GEP->use_empty()) {
979 LoadInst *L = cast<LoadInst>(GEP->user_back());
980 L->replaceAllUsesWith(TheArg);
981 AA.replaceWithNewValue(L, TheArg);
982 L->eraseFromParent();
985 GEP->eraseFromParent();
989 // Increment I2 past all of the arguments added for this promoted pointer.
990 std::advance(I2, ArgIndices.size());
993 // Tell the alias analysis that the old function is about to disappear.
994 AA.replaceWithNewValue(F, NF);
997 NF_CGN->stealCalledFunctionsFrom(CG[F]);
999 // Now that the old function is dead, delete it. If there is a dangling
1000 // reference to the CallgraphNode, just leave the dead function around for
1001 // someone else to nuke.
1002 CallGraphNode *CGN = CG[F];
1003 if (CGN->getNumReferences() == 0)
1004 delete CG.removeFunctionFromModule(CGN);
1006 F->setLinkage(Function::ExternalLinkage);
1011 bool ArgPromotion::doInitialization(CallGraph &CG) {
1012 FunctionDIs = makeSubprogramMap(CG.getModule());
1013 return CallGraphSCCPass::doInitialization(CG);