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/Analysis/ValueTracking.h"
40 #include "llvm/IR/CFG.h"
41 #include "llvm/IR/CallSite.h"
42 #include "llvm/IR/Constants.h"
43 #include "llvm/IR/DataLayout.h"
44 #include "llvm/IR/DebugInfo.h"
45 #include "llvm/IR/DerivedTypes.h"
46 #include "llvm/IR/Instructions.h"
47 #include "llvm/IR/LLVMContext.h"
48 #include "llvm/IR/Module.h"
49 #include "llvm/Support/Debug.h"
50 #include "llvm/Support/raw_ostream.h"
54 #define DEBUG_TYPE "argpromotion"
56 STATISTIC(NumArgumentsPromoted , "Number of pointer arguments promoted");
57 STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
58 STATISTIC(NumByValArgsPromoted , "Number of byval arguments promoted");
59 STATISTIC(NumArgumentsDead , "Number of dead pointer args eliminated");
62 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
64 struct ArgPromotion : public CallGraphSCCPass {
65 void getAnalysisUsage(AnalysisUsage &AU) const override {
66 AU.addRequired<AliasAnalysis>();
67 CallGraphSCCPass::getAnalysisUsage(AU);
70 bool runOnSCC(CallGraphSCC &SCC) override;
71 static char ID; // Pass identification, replacement for typeid
72 explicit ArgPromotion(unsigned maxElements = 3)
73 : CallGraphSCCPass(ID), maxElements(maxElements) {
74 initializeArgPromotionPass(*PassRegistry::getPassRegistry());
77 /// A vector used to hold the indices of a single GEP instruction
78 typedef std::vector<uint64_t> IndicesVector;
81 bool isDenselyPacked(Type *type, const DataLayout &DL);
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, const DataLayout &DL) {
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.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) ||
145 isDenselyPacked(seqTy->getElementType(), DL);
147 // Check for padding within and between elements of a struct.
148 StructType *StructTy = cast<StructType>(type);
149 const StructLayout *Layout = DL.getStructLayout(StructTy);
150 uint64_t StartPos = 0;
151 for (unsigned i = 0, E = StructTy->getNumElements(); i < E; ++i) {
152 Type *ElTy = StructTy->getElementType(i);
153 if (!isDenselyPacked(ElTy, DL))
155 if (StartPos != Layout->getElementOffsetInBits(i))
157 StartPos += DL.getTypeAllocSizeInBits(ElTy);
163 /// \brief Checks if the padding bytes of an argument could be accessed.
164 bool ArgPromotion::canPaddingBeAccessed(Argument *arg) {
166 assert(arg->hasByValAttr());
168 // Track all the pointers to the argument to make sure they are not captured.
169 SmallPtrSet<Value *, 16> PtrValues;
170 PtrValues.insert(arg);
172 // Track all of the stores.
173 SmallVector<StoreInst *, 16> Stores;
175 // Scan through the uses recursively to make sure the pointer is always used
177 SmallVector<Value *, 16> WorkList;
178 WorkList.insert(WorkList.end(), arg->user_begin(), arg->user_end());
179 while (!WorkList.empty()) {
180 Value *V = WorkList.back();
182 if (isa<GetElementPtrInst>(V) || isa<PHINode>(V)) {
183 if (PtrValues.insert(V).second)
184 WorkList.insert(WorkList.end(), V->user_begin(), V->user_end());
185 } else if (StoreInst *Store = dyn_cast<StoreInst>(V)) {
186 Stores.push_back(Store);
187 } else if (!isa<LoadInst>(V)) {
192 // Check to make sure the pointers aren't captured
193 for (StoreInst *Store : Stores)
194 if (PtrValues.count(Store->getValueOperand()))
200 /// PromoteArguments - This method checks the specified function to see if there
201 /// are any promotable arguments and if it is safe to promote the function (for
202 /// example, all callers are direct). If safe to promote some arguments, it
203 /// calls the DoPromotion method.
205 CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
206 Function *F = CGN->getFunction();
208 // Make sure that it is local to this module.
209 if (!F || !F->hasLocalLinkage()) return nullptr;
211 // Don't promote arguments for variadic functions. Adding, removing, or
212 // changing non-pack parameters can change the classification of pack
213 // parameters. Frontends encode that classification at the call site in the
214 // IR, while in the callee the classification is determined dynamically based
215 // on the number of registers consumed so far.
216 if (F->isVarArg()) return nullptr;
218 // First check: see if there are any pointer arguments! If not, quick exit.
219 SmallVector<Argument*, 16> PointerArgs;
220 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E; ++I)
221 if (I->getType()->isPointerTy())
222 PointerArgs.push_back(I);
223 if (PointerArgs.empty()) return nullptr;
225 // Second check: make sure that all callers are direct callers. We can't
226 // transform functions that have indirect callers. Also see if the function
227 // is self-recursive.
228 bool isSelfRecursive = false;
229 for (Use &U : F->uses()) {
230 CallSite CS(U.getUser());
231 // Must be a direct call.
232 if (CS.getInstruction() == nullptr || !CS.isCallee(&U)) return nullptr;
234 if (CS.getInstruction()->getParent()->getParent() == F)
235 isSelfRecursive = true;
238 const DataLayout &DL = F->getParent()->getDataLayout();
240 // Check to see which arguments are promotable. If an argument is promotable,
241 // add it to ArgsToPromote.
242 SmallPtrSet<Argument*, 8> ArgsToPromote;
243 SmallPtrSet<Argument*, 8> ByValArgsToTransform;
244 for (unsigned i = 0, e = PointerArgs.size(); i != e; ++i) {
245 Argument *PtrArg = PointerArgs[i];
246 Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
248 // Replace sret attribute with noalias. This reduces register pressure by
249 // avoiding a register copy.
250 if (PtrArg->hasStructRetAttr()) {
251 unsigned ArgNo = PtrArg->getArgNo();
254 .removeAttribute(F->getContext(), ArgNo + 1, Attribute::StructRet)
255 .addAttribute(F->getContext(), ArgNo + 1, Attribute::NoAlias));
256 for (Use &U : F->uses()) {
257 CallSite CS(U.getUser());
260 .removeAttribute(F->getContext(), ArgNo + 1,
261 Attribute::StructRet)
262 .addAttribute(F->getContext(), ArgNo + 1, Attribute::NoAlias));
266 // If this is a byval argument, and if the aggregate type is small, just
267 // pass the elements, which is always safe, if the passed value is densely
268 // packed or if we can prove the padding bytes are never accessed. This does
269 // not apply to inalloca.
270 bool isSafeToPromote =
271 PtrArg->hasByValAttr() &&
272 (isDenselyPacked(AgTy, DL) || !canPaddingBeAccessed(PtrArg));
273 if (isSafeToPromote) {
274 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
275 if (maxElements > 0 && STy->getNumElements() > maxElements) {
276 DEBUG(dbgs() << "argpromotion disable promoting argument '"
277 << PtrArg->getName() << "' because it would require adding more"
278 << " than " << maxElements << " arguments to the function.\n");
282 // If all the elements are single-value types, we can promote it.
283 bool AllSimple = true;
284 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
285 if (!STy->getElementType(i)->isSingleValueType()) {
291 // Safe to transform, don't even bother trying to "promote" it.
292 // Passing the elements as a scalar will allow scalarrepl to hack on
293 // the new alloca we introduce.
295 ByValArgsToTransform.insert(PtrArg);
301 // If the argument is a recursive type and we're in a recursive
302 // function, we could end up infinitely peeling the function argument.
303 if (isSelfRecursive) {
304 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
305 bool RecursiveType = false;
306 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
307 if (STy->getElementType(i) == PtrArg->getType()) {
308 RecursiveType = true;
317 // Otherwise, see if we can promote the pointer to its value.
318 if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValOrInAllocaAttr()))
319 ArgsToPromote.insert(PtrArg);
322 // No promotable pointer arguments.
323 if (ArgsToPromote.empty() && ByValArgsToTransform.empty())
326 return DoPromotion(F, ArgsToPromote, ByValArgsToTransform);
329 /// AllCallersPassInValidPointerForArgument - Return true if we can prove that
330 /// all callees pass in a valid pointer for the specified function argument.
331 static bool AllCallersPassInValidPointerForArgument(Argument *Arg) {
332 Function *Callee = Arg->getParent();
333 const DataLayout &DL = Callee->getParent()->getDataLayout();
335 unsigned ArgNo = Arg->getArgNo();
337 // Look at all call sites of the function. At this pointer we know we only
338 // have direct callees.
339 for (User *U : Callee->users()) {
341 assert(CS && "Should only have direct calls!");
343 if (!isDereferenceablePointer(CS.getArgument(ArgNo), DL))
349 /// Returns true if Prefix is a prefix of longer. That means, Longer has a size
350 /// that is greater than or equal to the size of prefix, and each of the
351 /// elements in Prefix is the same as the corresponding elements in Longer.
353 /// This means it also returns true when Prefix and Longer are equal!
354 static bool IsPrefix(const ArgPromotion::IndicesVector &Prefix,
355 const ArgPromotion::IndicesVector &Longer) {
356 if (Prefix.size() > Longer.size())
358 return std::equal(Prefix.begin(), Prefix.end(), Longer.begin());
362 /// Checks if Indices, or a prefix of Indices, is in Set.
363 static bool PrefixIn(const ArgPromotion::IndicesVector &Indices,
364 std::set<ArgPromotion::IndicesVector> &Set) {
365 std::set<ArgPromotion::IndicesVector>::iterator Low;
366 Low = Set.upper_bound(Indices);
367 if (Low != Set.begin())
369 // Low is now the last element smaller than or equal to Indices. This means
370 // it points to a prefix of Indices (possibly Indices itself), if such
373 // This load is safe if any prefix of its operands is safe to load.
374 return Low != Set.end() && IsPrefix(*Low, Indices);
377 /// Mark the given indices (ToMark) as safe in the given set of indices
378 /// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
379 /// is already a prefix of Indices in Safe, Indices are implicitely marked safe
380 /// already. Furthermore, any indices that Indices is itself a prefix of, are
381 /// removed from Safe (since they are implicitely safe because of Indices now).
382 static void MarkIndicesSafe(const ArgPromotion::IndicesVector &ToMark,
383 std::set<ArgPromotion::IndicesVector> &Safe) {
384 std::set<ArgPromotion::IndicesVector>::iterator Low;
385 Low = Safe.upper_bound(ToMark);
386 // Guard against the case where Safe is empty
387 if (Low != Safe.begin())
389 // Low is now the last element smaller than or equal to Indices. This
390 // means it points to a prefix of Indices (possibly Indices itself), if
391 // such prefix exists.
392 if (Low != Safe.end()) {
393 if (IsPrefix(*Low, ToMark))
394 // If there is already a prefix of these indices (or exactly these
395 // indices) marked a safe, don't bother adding these indices
398 // Increment Low, so we can use it as a "insert before" hint
402 Low = Safe.insert(Low, ToMark);
404 // If there we're a prefix of longer index list(s), remove those
405 std::set<ArgPromotion::IndicesVector>::iterator End = Safe.end();
406 while (Low != End && IsPrefix(ToMark, *Low)) {
407 std::set<ArgPromotion::IndicesVector>::iterator Remove = Low;
413 /// isSafeToPromoteArgument - As you might guess from the name of this method,
414 /// it checks to see if it is both safe and useful to promote the argument.
415 /// This method limits promotion of aggregates to only promote up to three
416 /// elements of the aggregate in order to avoid exploding the number of
417 /// arguments passed in.
418 bool ArgPromotion::isSafeToPromoteArgument(Argument *Arg,
419 bool isByValOrInAlloca) const {
420 typedef std::set<IndicesVector> GEPIndicesSet;
422 // Quick exit for unused arguments
423 if (Arg->use_empty())
426 // We can only promote this argument if all of the uses are loads, or are GEP
427 // instructions (with constant indices) that are subsequently loaded.
429 // Promoting the argument causes it to be loaded in the caller
430 // unconditionally. This is only safe if we can prove that either the load
431 // would have happened in the callee anyway (ie, there is a load in the entry
432 // block) or the pointer passed in at every call site is guaranteed to be
434 // In the former case, invalid loads can happen, but would have happened
435 // anyway, in the latter case, invalid loads won't happen. This prevents us
436 // from introducing an invalid load that wouldn't have happened in the
439 // This set will contain all sets of indices that are loaded in the entry
440 // block, and thus are safe to unconditionally load in the caller.
442 // This optimization is also safe for InAlloca parameters, because it verifies
443 // that the address isn't captured.
444 GEPIndicesSet SafeToUnconditionallyLoad;
446 // This set contains all the sets of indices that we are planning to promote.
447 // This makes it possible to limit the number of arguments added.
448 GEPIndicesSet ToPromote;
450 // If the pointer is always valid, any load with first index 0 is valid.
451 if (isByValOrInAlloca || AllCallersPassInValidPointerForArgument(Arg))
452 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
454 // First, iterate the entry block and mark loads of (geps of) arguments as
456 BasicBlock *EntryBlock = Arg->getParent()->begin();
457 // Declare this here so we can reuse it
458 IndicesVector Indices;
459 for (BasicBlock::iterator I = EntryBlock->begin(), E = EntryBlock->end();
461 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
462 Value *V = LI->getPointerOperand();
463 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
464 V = GEP->getPointerOperand();
466 // This load actually loads (part of) Arg? Check the indices then.
467 Indices.reserve(GEP->getNumIndices());
468 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
470 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
471 Indices.push_back(CI->getSExtValue());
473 // We found a non-constant GEP index for this argument? Bail out
474 // right away, can't promote this argument at all.
477 // Indices checked out, mark them as safe
478 MarkIndicesSafe(Indices, SafeToUnconditionallyLoad);
481 } else if (V == Arg) {
482 // Direct loads are equivalent to a GEP with a single 0 index.
483 MarkIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
487 // Now, iterate all uses of the argument to see if there are any uses that are
488 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
489 SmallVector<LoadInst*, 16> Loads;
490 IndicesVector Operands;
491 for (Use &U : Arg->uses()) {
492 User *UR = U.getUser();
494 if (LoadInst *LI = dyn_cast<LoadInst>(UR)) {
495 // Don't hack volatile/atomic loads
496 if (!LI->isSimple()) return false;
498 // Direct loads are equivalent to a GEP with a zero index and then a load.
499 Operands.push_back(0);
500 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UR)) {
501 if (GEP->use_empty()) {
502 // Dead GEP's cause trouble later. Just remove them if we run into
504 getAnalysis<AliasAnalysis>().deleteValue(GEP);
505 GEP->eraseFromParent();
506 // TODO: This runs the above loop over and over again for dead GEPs
507 // Couldn't we just do increment the UI iterator earlier and erase the
509 return isSafeToPromoteArgument(Arg, isByValOrInAlloca);
512 // Ensure that all of the indices are constants.
513 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end();
515 if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
516 Operands.push_back(C->getSExtValue());
518 return false; // Not a constant operand GEP!
520 // Ensure that the only users of the GEP are load instructions.
521 for (User *GEPU : GEP->users())
522 if (LoadInst *LI = dyn_cast<LoadInst>(GEPU)) {
523 // Don't hack volatile/atomic loads
524 if (!LI->isSimple()) return false;
527 // Other uses than load?
531 return false; // Not a load or a GEP.
534 // Now, see if it is safe to promote this load / loads of this GEP. Loading
535 // is safe if Operands, or a prefix of Operands, is marked as safe.
536 if (!PrefixIn(Operands, SafeToUnconditionallyLoad))
539 // See if we are already promoting a load with these indices. If not, check
540 // to make sure that we aren't promoting too many elements. If so, nothing
542 if (ToPromote.find(Operands) == ToPromote.end()) {
543 if (maxElements > 0 && ToPromote.size() == maxElements) {
544 DEBUG(dbgs() << "argpromotion not promoting argument '"
545 << Arg->getName() << "' because it would require adding more "
546 << "than " << maxElements << " arguments to the function.\n");
547 // We limit aggregate promotion to only promoting up to a fixed number
548 // of elements of the aggregate.
551 ToPromote.insert(std::move(Operands));
555 if (Loads.empty()) return true; // No users, this is a dead argument.
557 // Okay, now we know that the argument is only used by load instructions and
558 // it is safe to unconditionally perform all of them. Use alias analysis to
559 // check to see if the pointer is guaranteed to not be modified from entry of
560 // the function to each of the load instructions.
562 // Because there could be several/many load instructions, remember which
563 // blocks we know to be transparent to the load.
564 SmallPtrSet<BasicBlock*, 16> TranspBlocks;
566 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
568 for (unsigned i = 0, e = Loads.size(); i != e; ++i) {
569 // Check to see if the load is invalidated from the start of the block to
571 LoadInst *Load = Loads[i];
572 BasicBlock *BB = Load->getParent();
574 AliasAnalysis::Location Loc = MemoryLocation::get(Load);
575 if (AA.canInstructionRangeModRef(BB->front(), *Load, Loc,
577 return false; // Pointer is invalidated!
579 // Now check every path from the entry block to the load for transparency.
580 // To do this, we perform a depth first search on the inverse CFG from the
582 for (BasicBlock *P : predecessors(BB)) {
583 for (BasicBlock *TranspBB : inverse_depth_first_ext(P, TranspBlocks))
584 if (AA.canBasicBlockModify(*TranspBB, Loc))
589 // If the path from the entry of the function to each load is free of
590 // instructions that potentially invalidate the load, we can make the
595 /// DoPromotion - This method actually performs the promotion of the specified
596 /// arguments, and returns the new function. At this point, we know that it's
598 CallGraphNode *ArgPromotion::DoPromotion(Function *F,
599 SmallPtrSetImpl<Argument*> &ArgsToPromote,
600 SmallPtrSetImpl<Argument*> &ByValArgsToTransform) {
602 // Start by computing a new prototype for the function, which is the same as
603 // the old function, but has modified arguments.
604 FunctionType *FTy = F->getFunctionType();
605 std::vector<Type*> Params;
607 typedef std::set<std::pair<Type *, IndicesVector>> ScalarizeTable;
609 // ScalarizedElements - If we are promoting a pointer that has elements
610 // accessed out of it, keep track of which elements are accessed so that we
611 // can add one argument for each.
613 // Arguments that are directly loaded will have a zero element value here, to
614 // handle cases where there are both a direct load and GEP accesses.
616 std::map<Argument*, ScalarizeTable> ScalarizedElements;
618 // OriginalLoads - Keep track of a representative load instruction from the
619 // original function so that we can tell the alias analysis implementation
620 // what the new GEP/Load instructions we are inserting look like.
621 // We need to keep the original loads for each argument and the elements
622 // of the argument that are accessed.
623 std::map<std::pair<Argument*, IndicesVector>, LoadInst*> OriginalLoads;
625 // Attribute - Keep track of the parameter attributes for the arguments
626 // that we are *not* promoting. For the ones that we do promote, the parameter
627 // attributes are lost
628 SmallVector<AttributeSet, 8> AttributesVec;
629 const AttributeSet &PAL = F->getAttributes();
631 // Add any return attributes.
632 if (PAL.hasAttributes(AttributeSet::ReturnIndex))
633 AttributesVec.push_back(AttributeSet::get(F->getContext(),
634 PAL.getRetAttributes()));
636 // First, determine the new argument list
637 unsigned ArgIndex = 1;
638 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
640 if (ByValArgsToTransform.count(I)) {
641 // Simple byval argument? Just add all the struct element types.
642 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
643 StructType *STy = cast<StructType>(AgTy);
644 Params.insert(Params.end(), STy->element_begin(), STy->element_end());
645 ++NumByValArgsPromoted;
646 } else if (!ArgsToPromote.count(I)) {
647 // Unchanged argument
648 Params.push_back(I->getType());
649 AttributeSet attrs = PAL.getParamAttributes(ArgIndex);
650 if (attrs.hasAttributes(ArgIndex)) {
651 AttrBuilder B(attrs, ArgIndex);
653 push_back(AttributeSet::get(F->getContext(), Params.size(), B));
655 } else if (I->use_empty()) {
656 // Dead argument (which are always marked as promotable)
659 // Okay, this is being promoted. This means that the only uses are loads
660 // or GEPs which are only used by loads
662 // In this table, we will track which indices are loaded from the argument
663 // (where direct loads are tracked as no indices).
664 ScalarizeTable &ArgIndices = ScalarizedElements[I];
665 for (User *U : I->users()) {
666 Instruction *UI = cast<Instruction>(U);
668 if (LoadInst *L = dyn_cast<LoadInst>(UI))
669 SrcTy = L->getType();
671 SrcTy = cast<GetElementPtrInst>(UI)->getSourceElementType();
672 IndicesVector Indices;
673 Indices.reserve(UI->getNumOperands() - 1);
674 // Since loads will only have a single operand, and GEPs only a single
675 // non-index operand, this will record direct loads without any indices,
676 // and gep+loads with the GEP indices.
677 for (User::op_iterator II = UI->op_begin() + 1, IE = UI->op_end();
679 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
680 // GEPs with a single 0 index can be merged with direct loads
681 if (Indices.size() == 1 && Indices.front() == 0)
683 ArgIndices.insert(std::make_pair(SrcTy, Indices));
685 if (LoadInst *L = dyn_cast<LoadInst>(UI))
688 // Take any load, we will use it only to update Alias Analysis
689 OrigLoad = cast<LoadInst>(UI->user_back());
690 OriginalLoads[std::make_pair(I, Indices)] = OrigLoad;
693 // Add a parameter to the function for each element passed in.
694 for (ScalarizeTable::iterator SI = ArgIndices.begin(),
695 E = ArgIndices.end(); SI != E; ++SI) {
696 // not allowed to dereference ->begin() if size() is 0
697 Params.push_back(GetElementPtrInst::getIndexedType(
698 cast<PointerType>(I->getType()->getScalarType())->getElementType(),
700 assert(Params.back());
703 if (ArgIndices.size() == 1 && ArgIndices.begin()->second.empty())
704 ++NumArgumentsPromoted;
706 ++NumAggregatesPromoted;
710 // Add any function attributes.
711 if (PAL.hasAttributes(AttributeSet::FunctionIndex))
712 AttributesVec.push_back(AttributeSet::get(FTy->getContext(),
713 PAL.getFnAttributes()));
715 Type *RetTy = FTy->getReturnType();
717 // Construct the new function type using the new arguments.
718 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
720 // Create the new function body and insert it into the module.
721 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
722 NF->copyAttributesFrom(F);
724 // Patch the pointer to LLVM function in debug info descriptor.
725 auto DI = FunctionDIs.find(F);
726 if (DI != FunctionDIs.end()) {
727 DISubprogram *SP = DI->second;
728 SP->replaceFunction(NF);
729 // Ensure the map is updated so it can be reused on subsequent argument
730 // promotions of the same function.
731 FunctionDIs.erase(DI);
732 FunctionDIs[NF] = SP;
735 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n"
738 // Recompute the parameter attributes list based on the new arguments for
740 NF->setAttributes(AttributeSet::get(F->getContext(), AttributesVec));
741 AttributesVec.clear();
743 F->getParent()->getFunctionList().insert(F, NF);
746 // Get the alias analysis information that we need to update to reflect our
748 AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
750 // Get the callgraph information that we need to update to reflect our
752 CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
754 // Get a new callgraph node for NF.
755 CallGraphNode *NF_CGN = CG.getOrInsertFunction(NF);
757 // Loop over all of the callers of the function, transforming the call sites
758 // to pass in the loaded pointers.
760 SmallVector<Value*, 16> Args;
761 while (!F->use_empty()) {
762 CallSite CS(F->user_back());
763 assert(CS.getCalledFunction() == F);
764 Instruction *Call = CS.getInstruction();
765 const AttributeSet &CallPAL = CS.getAttributes();
767 // Add any return attributes.
768 if (CallPAL.hasAttributes(AttributeSet::ReturnIndex))
769 AttributesVec.push_back(AttributeSet::get(F->getContext(),
770 CallPAL.getRetAttributes()));
772 // Loop over the operands, inserting GEP and loads in the caller as
774 CallSite::arg_iterator AI = CS.arg_begin();
776 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end();
777 I != E; ++I, ++AI, ++ArgIndex)
778 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
779 Args.push_back(*AI); // Unmodified argument
781 if (CallPAL.hasAttributes(ArgIndex)) {
782 AttrBuilder B(CallPAL, ArgIndex);
784 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
786 } else if (ByValArgsToTransform.count(I)) {
787 // Emit a GEP and load for each element of the struct.
788 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
789 StructType *STy = cast<StructType>(AgTy);
791 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr };
792 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
793 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
794 Value *Idx = GetElementPtrInst::Create(
795 STy, *AI, Idxs, (*AI)->getName() + "." + Twine(i), Call);
796 // TODO: Tell AA about the new values?
797 Args.push_back(new LoadInst(Idx, Idx->getName()+".val", Call));
799 } else if (!I->use_empty()) {
800 // Non-dead argument: insert GEPs and loads as appropriate.
801 ScalarizeTable &ArgIndices = ScalarizedElements[I];
802 // Store the Value* version of the indices in here, but declare it now
804 std::vector<Value*> Ops;
805 for (ScalarizeTable::iterator SI = ArgIndices.begin(),
806 E = ArgIndices.end(); SI != E; ++SI) {
808 LoadInst *OrigLoad = OriginalLoads[std::make_pair(I, SI->second)];
809 if (!SI->second.empty()) {
810 Ops.reserve(SI->second.size());
811 Type *ElTy = V->getType();
812 for (IndicesVector::const_iterator II = SI->second.begin(),
813 IE = SI->second.end();
815 // Use i32 to index structs, and i64 for others (pointers/arrays).
816 // This satisfies GEP constraints.
817 Type *IdxTy = (ElTy->isStructTy() ?
818 Type::getInt32Ty(F->getContext()) :
819 Type::getInt64Ty(F->getContext()));
820 Ops.push_back(ConstantInt::get(IdxTy, *II));
821 // Keep track of the type we're currently indexing.
822 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(*II);
824 // And create a GEP to extract those indices.
825 V = GetElementPtrInst::Create(SI->first, V, Ops,
826 V->getName() + ".idx", Call);
828 AA.copyValue(OrigLoad->getOperand(0), V);
830 // Since we're replacing a load make sure we take the alignment
831 // of the previous load.
832 LoadInst *newLoad = new LoadInst(V, V->getName()+".val", Call);
833 newLoad->setAlignment(OrigLoad->getAlignment());
834 // Transfer the AA info too.
836 OrigLoad->getAAMetadata(AAInfo);
837 newLoad->setAAMetadata(AAInfo);
839 Args.push_back(newLoad);
840 AA.copyValue(OrigLoad, Args.back());
844 // Push any varargs arguments on the list.
845 for (; AI != CS.arg_end(); ++AI, ++ArgIndex) {
847 if (CallPAL.hasAttributes(ArgIndex)) {
848 AttrBuilder B(CallPAL, ArgIndex);
850 push_back(AttributeSet::get(F->getContext(), Args.size(), B));
854 // Add any function attributes.
855 if (CallPAL.hasAttributes(AttributeSet::FunctionIndex))
856 AttributesVec.push_back(AttributeSet::get(Call->getContext(),
857 CallPAL.getFnAttributes()));
860 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
861 New = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
863 cast<InvokeInst>(New)->setCallingConv(CS.getCallingConv());
864 cast<InvokeInst>(New)->setAttributes(AttributeSet::get(II->getContext(),
867 New = CallInst::Create(NF, Args, "", Call);
868 cast<CallInst>(New)->setCallingConv(CS.getCallingConv());
869 cast<CallInst>(New)->setAttributes(AttributeSet::get(New->getContext(),
871 if (cast<CallInst>(Call)->isTailCall())
872 cast<CallInst>(New)->setTailCall();
874 New->setDebugLoc(Call->getDebugLoc());
876 AttributesVec.clear();
878 // Update the alias analysis implementation to know that we are replacing
879 // the old call with a new one.
880 AA.replaceWithNewValue(Call, New);
882 // Update the callgraph to know that the callsite has been transformed.
883 CallGraphNode *CalleeNode = CG[Call->getParent()->getParent()];
884 CalleeNode->replaceCallEdge(CS, CallSite(New), NF_CGN);
886 if (!Call->use_empty()) {
887 Call->replaceAllUsesWith(New);
891 // Finally, remove the old call from the program, reducing the use-count of
893 Call->eraseFromParent();
896 // Since we have now created the new function, splice the body of the old
897 // function right into the new function, leaving the old rotting hulk of the
899 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
901 // Loop over the argument list, transferring uses of the old arguments over to
902 // the new arguments, also transferring over the names as well.
904 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
905 I2 = NF->arg_begin(); I != E; ++I) {
906 if (!ArgsToPromote.count(I) && !ByValArgsToTransform.count(I)) {
907 // If this is an unmodified argument, move the name and users over to the
909 I->replaceAllUsesWith(I2);
911 AA.replaceWithNewValue(I, I2);
916 if (ByValArgsToTransform.count(I)) {
917 // In the callee, we create an alloca, and store each of the new incoming
918 // arguments into the alloca.
919 Instruction *InsertPt = NF->begin()->begin();
921 // Just add all the struct element types.
922 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
923 Value *TheAlloca = new AllocaInst(AgTy, nullptr, "", InsertPt);
924 StructType *STy = cast<StructType>(AgTy);
926 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr };
928 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
929 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
930 Value *Idx = GetElementPtrInst::Create(
931 AgTy, TheAlloca, Idxs, TheAlloca->getName() + "." + Twine(i),
933 I2->setName(I->getName()+"."+Twine(i));
934 new StoreInst(I2++, Idx, InsertPt);
937 // Anything that used the arg should now use the alloca.
938 I->replaceAllUsesWith(TheAlloca);
939 TheAlloca->takeName(I);
940 AA.replaceWithNewValue(I, TheAlloca);
942 // If the alloca is used in a call, we must clear the tail flag since
943 // the callee now uses an alloca from the caller.
944 for (User *U : TheAlloca->users()) {
945 CallInst *Call = dyn_cast<CallInst>(U);
948 Call->setTailCall(false);
953 if (I->use_empty()) {
958 // Otherwise, if we promoted this argument, then all users are load
959 // instructions (or GEPs with only load users), and all loads should be
960 // using the new argument that we added.
961 ScalarizeTable &ArgIndices = ScalarizedElements[I];
963 while (!I->use_empty()) {
964 if (LoadInst *LI = dyn_cast<LoadInst>(I->user_back())) {
965 assert(ArgIndices.begin()->second.empty() &&
966 "Load element should sort to front!");
967 I2->setName(I->getName()+".val");
968 LI->replaceAllUsesWith(I2);
969 AA.replaceWithNewValue(LI, I2);
970 LI->eraseFromParent();
971 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName()
972 << "' in function '" << F->getName() << "'\n");
974 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->user_back());
975 IndicesVector Operands;
976 Operands.reserve(GEP->getNumIndices());
977 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
979 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
981 // GEPs with a single 0 index can be merged with direct loads
982 if (Operands.size() == 1 && Operands.front() == 0)
985 Function::arg_iterator TheArg = I2;
986 for (ScalarizeTable::iterator It = ArgIndices.begin();
987 It->second != Operands; ++It, ++TheArg) {
988 assert(It != ArgIndices.end() && "GEP not handled??");
991 std::string NewName = I->getName();
992 for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
993 NewName += "." + utostr(Operands[i]);
996 TheArg->setName(NewName);
998 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName()
999 << "' of function '" << NF->getName() << "'\n");
1001 // All of the uses must be load instructions. Replace them all with
1002 // the argument specified by ArgNo.
1003 while (!GEP->use_empty()) {
1004 LoadInst *L = cast<LoadInst>(GEP->user_back());
1005 L->replaceAllUsesWith(TheArg);
1006 AA.replaceWithNewValue(L, TheArg);
1007 L->eraseFromParent();
1009 AA.deleteValue(GEP);
1010 GEP->eraseFromParent();
1014 // Increment I2 past all of the arguments added for this promoted pointer.
1015 std::advance(I2, ArgIndices.size());
1018 // Tell the alias analysis that the old function is about to disappear.
1019 AA.replaceWithNewValue(F, NF);
1022 NF_CGN->stealCalledFunctionsFrom(CG[F]);
1024 // Now that the old function is dead, delete it. If there is a dangling
1025 // reference to the CallgraphNode, just leave the dead function around for
1026 // someone else to nuke.
1027 CallGraphNode *CGN = CG[F];
1028 if (CGN->getNumReferences() == 0)
1029 delete CG.removeFunctionFromModule(CGN);
1031 F->setLinkage(Function::ExternalLinkage);
1036 bool ArgPromotion::doInitialization(CallGraph &CG) {
1037 FunctionDIs = makeSubprogramMap(CG.getModule());
1038 return CallGraphSCCPass::doInitialization(CG);