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/ArgumentPromotion.h"
33 #include "llvm/ADT/DepthFirstIterator.h"
34 #include "llvm/ADT/Optional.h"
35 #include "llvm/ADT/Statistic.h"
36 #include "llvm/ADT/StringExtras.h"
37 #include "llvm/Analysis/AliasAnalysis.h"
38 #include "llvm/Analysis/AssumptionCache.h"
39 #include "llvm/Analysis/BasicAliasAnalysis.h"
40 #include "llvm/Analysis/CallGraph.h"
41 #include "llvm/Analysis/CallGraphSCCPass.h"
42 #include "llvm/Analysis/LazyCallGraph.h"
43 #include "llvm/Analysis/Loads.h"
44 #include "llvm/Analysis/TargetLibraryInfo.h"
45 #include "llvm/IR/CFG.h"
46 #include "llvm/IR/CallSite.h"
47 #include "llvm/IR/Constants.h"
48 #include "llvm/IR/DataLayout.h"
49 #include "llvm/IR/DebugInfo.h"
50 #include "llvm/IR/DerivedTypes.h"
51 #include "llvm/IR/Instructions.h"
52 #include "llvm/IR/LLVMContext.h"
53 #include "llvm/IR/Module.h"
54 #include "llvm/Support/Debug.h"
55 #include "llvm/Support/raw_ostream.h"
56 #include "llvm/Transforms/IPO.h"
60 #define DEBUG_TYPE "argpromotion"
62 STATISTIC(NumArgumentsPromoted, "Number of pointer arguments promoted");
63 STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
64 STATISTIC(NumByValArgsPromoted, "Number of byval arguments promoted");
65 STATISTIC(NumArgumentsDead, "Number of dead pointer args eliminated");
67 /// A vector used to hold the indices of a single GEP instruction
68 typedef std::vector<uint64_t> IndicesVector;
70 /// DoPromotion - This method actually performs the promotion of the specified
71 /// arguments, and returns the new function. At this point, we know that it's
74 doPromotion(Function *F, SmallPtrSetImpl<Argument *> &ArgsToPromote,
75 SmallPtrSetImpl<Argument *> &ByValArgsToTransform,
76 Optional<function_ref<void(CallSite OldCS, CallSite NewCS)>>
79 // Start by computing a new prototype for the function, which is the same as
80 // the old function, but has modified arguments.
81 FunctionType *FTy = F->getFunctionType();
82 std::vector<Type *> Params;
84 typedef std::set<std::pair<Type *, IndicesVector>> ScalarizeTable;
86 // ScalarizedElements - If we are promoting a pointer that has elements
87 // accessed out of it, keep track of which elements are accessed so that we
88 // can add one argument for each.
90 // Arguments that are directly loaded will have a zero element value here, to
91 // handle cases where there are both a direct load and GEP accesses.
93 std::map<Argument *, ScalarizeTable> ScalarizedElements;
95 // OriginalLoads - Keep track of a representative load instruction from the
96 // original function so that we can tell the alias analysis implementation
97 // what the new GEP/Load instructions we are inserting look like.
98 // We need to keep the original loads for each argument and the elements
99 // of the argument that are accessed.
100 std::map<std::pair<Argument *, IndicesVector>, LoadInst *> OriginalLoads;
102 // Attribute - Keep track of the parameter attributes for the arguments
103 // that we are *not* promoting. For the ones that we do promote, the parameter
104 // attributes are lost
105 SmallVector<AttributeSet, 8> ArgAttrVec;
106 AttributeList PAL = F->getAttributes();
108 // First, determine the new argument list
110 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
112 if (ByValArgsToTransform.count(&*I)) {
113 // Simple byval argument? Just add all the struct element types.
114 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
115 StructType *STy = cast<StructType>(AgTy);
116 Params.insert(Params.end(), STy->element_begin(), STy->element_end());
117 ArgAttrVec.insert(ArgAttrVec.end(), STy->getNumElements(),
119 ++NumByValArgsPromoted;
120 } else if (!ArgsToPromote.count(&*I)) {
121 // Unchanged argument
122 Params.push_back(I->getType());
123 ArgAttrVec.push_back(PAL.getParamAttributes(ArgNo));
124 } else if (I->use_empty()) {
125 // Dead argument (which are always marked as promotable)
128 // Okay, this is being promoted. This means that the only uses are loads
129 // or GEPs which are only used by loads
131 // In this table, we will track which indices are loaded from the argument
132 // (where direct loads are tracked as no indices).
133 ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
134 for (User *U : I->users()) {
135 Instruction *UI = cast<Instruction>(U);
137 if (LoadInst *L = dyn_cast<LoadInst>(UI))
138 SrcTy = L->getType();
140 SrcTy = cast<GetElementPtrInst>(UI)->getSourceElementType();
141 IndicesVector Indices;
142 Indices.reserve(UI->getNumOperands() - 1);
143 // Since loads will only have a single operand, and GEPs only a single
144 // non-index operand, this will record direct loads without any indices,
145 // and gep+loads with the GEP indices.
146 for (User::op_iterator II = UI->op_begin() + 1, IE = UI->op_end();
148 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
149 // GEPs with a single 0 index can be merged with direct loads
150 if (Indices.size() == 1 && Indices.front() == 0)
152 ArgIndices.insert(std::make_pair(SrcTy, Indices));
154 if (LoadInst *L = dyn_cast<LoadInst>(UI))
157 // Take any load, we will use it only to update Alias Analysis
158 OrigLoad = cast<LoadInst>(UI->user_back());
159 OriginalLoads[std::make_pair(&*I, Indices)] = OrigLoad;
162 // Add a parameter to the function for each element passed in.
163 for (const auto &ArgIndex : ArgIndices) {
164 // not allowed to dereference ->begin() if size() is 0
165 Params.push_back(GetElementPtrInst::getIndexedType(
166 cast<PointerType>(I->getType()->getScalarType())->getElementType(),
168 ArgAttrVec.push_back(AttributeSet());
169 assert(Params.back());
172 if (ArgIndices.size() == 1 && ArgIndices.begin()->second.empty())
173 ++NumArgumentsPromoted;
175 ++NumAggregatesPromoted;
179 Type *RetTy = FTy->getReturnType();
181 // Construct the new function type using the new arguments.
182 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
184 // Create the new function body and insert it into the module.
185 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getName());
186 NF->copyAttributesFrom(F);
188 // Patch the pointer to LLVM function in debug info descriptor.
189 NF->setSubprogram(F->getSubprogram());
190 F->setSubprogram(nullptr);
192 DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n"
195 // Recompute the parameter attributes list based on the new arguments for
197 NF->setAttributes(AttributeList::get(F->getContext(), PAL.getFnAttributes(),
198 PAL.getRetAttributes(), ArgAttrVec));
201 F->getParent()->getFunctionList().insert(F->getIterator(), NF);
204 // Loop over all of the callers of the function, transforming the call sites
205 // to pass in the loaded pointers.
207 SmallVector<Value *, 16> Args;
208 while (!F->use_empty()) {
209 CallSite CS(F->user_back());
210 assert(CS.getCalledFunction() == F);
211 Instruction *Call = CS.getInstruction();
212 const AttributeList &CallPAL = CS.getAttributes();
214 // Loop over the operands, inserting GEP and loads in the caller as
216 CallSite::arg_iterator AI = CS.arg_begin();
218 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
220 if (!ArgsToPromote.count(&*I) && !ByValArgsToTransform.count(&*I)) {
221 Args.push_back(*AI); // Unmodified argument
222 ArgAttrVec.push_back(CallPAL.getParamAttributes(ArgNo));
223 } else if (ByValArgsToTransform.count(&*I)) {
224 // Emit a GEP and load for each element of the struct.
225 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
226 StructType *STy = cast<StructType>(AgTy);
228 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr};
229 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
230 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
231 Value *Idx = GetElementPtrInst::Create(
232 STy, *AI, Idxs, (*AI)->getName() + "." + Twine(i), Call);
233 // TODO: Tell AA about the new values?
234 Args.push_back(new LoadInst(Idx, Idx->getName() + ".val", Call));
235 ArgAttrVec.push_back(AttributeSet());
237 } else if (!I->use_empty()) {
238 // Non-dead argument: insert GEPs and loads as appropriate.
239 ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
240 // Store the Value* version of the indices in here, but declare it now
242 std::vector<Value *> Ops;
243 for (const auto &ArgIndex : ArgIndices) {
246 OriginalLoads[std::make_pair(&*I, ArgIndex.second)];
247 if (!ArgIndex.second.empty()) {
248 Ops.reserve(ArgIndex.second.size());
249 Type *ElTy = V->getType();
250 for (auto II : ArgIndex.second) {
251 // Use i32 to index structs, and i64 for others (pointers/arrays).
252 // This satisfies GEP constraints.
254 (ElTy->isStructTy() ? Type::getInt32Ty(F->getContext())
255 : Type::getInt64Ty(F->getContext()));
256 Ops.push_back(ConstantInt::get(IdxTy, II));
257 // Keep track of the type we're currently indexing.
258 if (auto *ElPTy = dyn_cast<PointerType>(ElTy))
259 ElTy = ElPTy->getElementType();
261 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(II);
263 // And create a GEP to extract those indices.
264 V = GetElementPtrInst::Create(ArgIndex.first, V, Ops,
265 V->getName() + ".idx", Call);
268 // Since we're replacing a load make sure we take the alignment
269 // of the previous load.
270 LoadInst *newLoad = new LoadInst(V, V->getName() + ".val", Call);
271 newLoad->setAlignment(OrigLoad->getAlignment());
272 // Transfer the AA info too.
274 OrigLoad->getAAMetadata(AAInfo);
275 newLoad->setAAMetadata(AAInfo);
277 Args.push_back(newLoad);
278 ArgAttrVec.push_back(AttributeSet());
282 // Push any varargs arguments on the list.
283 for (; AI != CS.arg_end(); ++AI, ++ArgNo) {
285 ArgAttrVec.push_back(CallPAL.getParamAttributes(ArgNo));
288 SmallVector<OperandBundleDef, 1> OpBundles;
289 CS.getOperandBundlesAsDefs(OpBundles);
292 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
293 NewCS = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
294 Args, OpBundles, "", Call);
296 auto *NewCall = CallInst::Create(NF, Args, OpBundles, "", Call);
297 NewCall->setTailCallKind(cast<CallInst>(Call)->getTailCallKind());
300 NewCS.setCallingConv(CS.getCallingConv());
302 AttributeList::get(F->getContext(), CallPAL.getFnAttributes(),
303 CallPAL.getRetAttributes(), ArgAttrVec));
304 NewCS->setDebugLoc(Call->getDebugLoc());
306 if (Call->extractProfTotalWeight(W))
307 NewCS->setProfWeight(W);
311 // Update the callgraph to know that the callsite has been transformed.
313 (*ReplaceCallSite)(CS, NewCS);
315 if (!Call->use_empty()) {
316 Call->replaceAllUsesWith(NewCS.getInstruction());
317 NewCS->takeName(Call);
320 // Finally, remove the old call from the program, reducing the use-count of
322 Call->eraseFromParent();
325 const DataLayout &DL = F->getParent()->getDataLayout();
327 // Since we have now created the new function, splice the body of the old
328 // function right into the new function, leaving the old rotting hulk of the
330 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
332 // Loop over the argument list, transferring uses of the old arguments over to
333 // the new arguments, also transferring over the names as well.
335 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
336 I2 = NF->arg_begin();
338 if (!ArgsToPromote.count(&*I) && !ByValArgsToTransform.count(&*I)) {
339 // If this is an unmodified argument, move the name and users over to the
341 I->replaceAllUsesWith(&*I2);
347 if (ByValArgsToTransform.count(&*I)) {
348 // In the callee, we create an alloca, and store each of the new incoming
349 // arguments into the alloca.
350 Instruction *InsertPt = &NF->begin()->front();
352 // Just add all the struct element types.
353 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
354 Value *TheAlloca = new AllocaInst(AgTy, DL.getAllocaAddrSpace(), nullptr,
356 StructType *STy = cast<StructType>(AgTy);
357 Value *Idxs[2] = {ConstantInt::get(Type::getInt32Ty(F->getContext()), 0),
360 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
361 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
362 Value *Idx = GetElementPtrInst::Create(
363 AgTy, TheAlloca, Idxs, TheAlloca->getName() + "." + Twine(i),
365 I2->setName(I->getName() + "." + Twine(i));
366 new StoreInst(&*I2++, Idx, InsertPt);
369 // Anything that used the arg should now use the alloca.
370 I->replaceAllUsesWith(TheAlloca);
371 TheAlloca->takeName(&*I);
373 // If the alloca is used in a call, we must clear the tail flag since
374 // the callee now uses an alloca from the caller.
375 for (User *U : TheAlloca->users()) {
376 CallInst *Call = dyn_cast<CallInst>(U);
379 Call->setTailCall(false);
387 // Otherwise, if we promoted this argument, then all users are load
388 // instructions (or GEPs with only load users), and all loads should be
389 // using the new argument that we added.
390 ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
392 while (!I->use_empty()) {
393 if (LoadInst *LI = dyn_cast<LoadInst>(I->user_back())) {
394 assert(ArgIndices.begin()->second.empty() &&
395 "Load element should sort to front!");
396 I2->setName(I->getName() + ".val");
397 LI->replaceAllUsesWith(&*I2);
398 LI->eraseFromParent();
399 DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName()
400 << "' in function '" << F->getName() << "'\n");
402 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->user_back());
403 IndicesVector Operands;
404 Operands.reserve(GEP->getNumIndices());
405 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
407 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
409 // GEPs with a single 0 index can be merged with direct loads
410 if (Operands.size() == 1 && Operands.front() == 0)
413 Function::arg_iterator TheArg = I2;
414 for (ScalarizeTable::iterator It = ArgIndices.begin();
415 It->second != Operands; ++It, ++TheArg) {
416 assert(It != ArgIndices.end() && "GEP not handled??");
419 std::string NewName = I->getName();
420 for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
421 NewName += "." + utostr(Operands[i]);
424 TheArg->setName(NewName);
426 DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName()
427 << "' of function '" << NF->getName() << "'\n");
429 // All of the uses must be load instructions. Replace them all with
430 // the argument specified by ArgNo.
431 while (!GEP->use_empty()) {
432 LoadInst *L = cast<LoadInst>(GEP->user_back());
433 L->replaceAllUsesWith(&*TheArg);
434 L->eraseFromParent();
436 GEP->eraseFromParent();
440 // Increment I2 past all of the arguments added for this promoted pointer.
441 std::advance(I2, ArgIndices.size());
447 /// AllCallersPassInValidPointerForArgument - Return true if we can prove that
448 /// all callees pass in a valid pointer for the specified function argument.
449 static bool allCallersPassInValidPointerForArgument(Argument *Arg) {
450 Function *Callee = Arg->getParent();
451 const DataLayout &DL = Callee->getParent()->getDataLayout();
453 unsigned ArgNo = Arg->getArgNo();
455 // Look at all call sites of the function. At this point we know we only have
457 for (User *U : Callee->users()) {
459 assert(CS && "Should only have direct calls!");
461 if (!isDereferenceablePointer(CS.getArgument(ArgNo), DL))
467 /// Returns true if Prefix is a prefix of longer. That means, Longer has a size
468 /// that is greater than or equal to the size of prefix, and each of the
469 /// elements in Prefix is the same as the corresponding elements in Longer.
471 /// This means it also returns true when Prefix and Longer are equal!
472 static bool isPrefix(const IndicesVector &Prefix, const IndicesVector &Longer) {
473 if (Prefix.size() > Longer.size())
475 return std::equal(Prefix.begin(), Prefix.end(), Longer.begin());
478 /// Checks if Indices, or a prefix of Indices, is in Set.
479 static bool prefixIn(const IndicesVector &Indices,
480 std::set<IndicesVector> &Set) {
481 std::set<IndicesVector>::iterator Low;
482 Low = Set.upper_bound(Indices);
483 if (Low != Set.begin())
485 // Low is now the last element smaller than or equal to Indices. This means
486 // it points to a prefix of Indices (possibly Indices itself), if such
489 // This load is safe if any prefix of its operands is safe to load.
490 return Low != Set.end() && isPrefix(*Low, Indices);
493 /// Mark the given indices (ToMark) as safe in the given set of indices
494 /// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
495 /// is already a prefix of Indices in Safe, Indices are implicitely marked safe
496 /// already. Furthermore, any indices that Indices is itself a prefix of, are
497 /// removed from Safe (since they are implicitely safe because of Indices now).
498 static void markIndicesSafe(const IndicesVector &ToMark,
499 std::set<IndicesVector> &Safe) {
500 std::set<IndicesVector>::iterator Low;
501 Low = Safe.upper_bound(ToMark);
502 // Guard against the case where Safe is empty
503 if (Low != Safe.begin())
505 // Low is now the last element smaller than or equal to Indices. This
506 // means it points to a prefix of Indices (possibly Indices itself), if
507 // such prefix exists.
508 if (Low != Safe.end()) {
509 if (isPrefix(*Low, ToMark))
510 // If there is already a prefix of these indices (or exactly these
511 // indices) marked a safe, don't bother adding these indices
514 // Increment Low, so we can use it as a "insert before" hint
518 Low = Safe.insert(Low, ToMark);
520 // If there we're a prefix of longer index list(s), remove those
521 std::set<IndicesVector>::iterator End = Safe.end();
522 while (Low != End && isPrefix(ToMark, *Low)) {
523 std::set<IndicesVector>::iterator Remove = Low;
529 /// isSafeToPromoteArgument - As you might guess from the name of this method,
530 /// it checks to see if it is both safe and useful to promote the argument.
531 /// This method limits promotion of aggregates to only promote up to three
532 /// elements of the aggregate in order to avoid exploding the number of
533 /// arguments passed in.
534 static bool isSafeToPromoteArgument(Argument *Arg, bool isByValOrInAlloca,
535 AAResults &AAR, unsigned MaxElements) {
536 typedef std::set<IndicesVector> GEPIndicesSet;
538 // Quick exit for unused arguments
539 if (Arg->use_empty())
542 // We can only promote this argument if all of the uses are loads, or are GEP
543 // instructions (with constant indices) that are subsequently loaded.
545 // Promoting the argument causes it to be loaded in the caller
546 // unconditionally. This is only safe if we can prove that either the load
547 // would have happened in the callee anyway (ie, there is a load in the entry
548 // block) or the pointer passed in at every call site is guaranteed to be
550 // In the former case, invalid loads can happen, but would have happened
551 // anyway, in the latter case, invalid loads won't happen. This prevents us
552 // from introducing an invalid load that wouldn't have happened in the
555 // This set will contain all sets of indices that are loaded in the entry
556 // block, and thus are safe to unconditionally load in the caller.
558 // This optimization is also safe for InAlloca parameters, because it verifies
559 // that the address isn't captured.
560 GEPIndicesSet SafeToUnconditionallyLoad;
562 // This set contains all the sets of indices that we are planning to promote.
563 // This makes it possible to limit the number of arguments added.
564 GEPIndicesSet ToPromote;
566 // If the pointer is always valid, any load with first index 0 is valid.
567 if (isByValOrInAlloca || allCallersPassInValidPointerForArgument(Arg))
568 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
570 // First, iterate the entry block and mark loads of (geps of) arguments as
572 BasicBlock &EntryBlock = Arg->getParent()->front();
573 // Declare this here so we can reuse it
574 IndicesVector Indices;
575 for (Instruction &I : EntryBlock)
576 if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
577 Value *V = LI->getPointerOperand();
578 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
579 V = GEP->getPointerOperand();
581 // This load actually loads (part of) Arg? Check the indices then.
582 Indices.reserve(GEP->getNumIndices());
583 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
585 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
586 Indices.push_back(CI->getSExtValue());
588 // We found a non-constant GEP index for this argument? Bail out
589 // right away, can't promote this argument at all.
592 // Indices checked out, mark them as safe
593 markIndicesSafe(Indices, SafeToUnconditionallyLoad);
596 } else if (V == Arg) {
597 // Direct loads are equivalent to a GEP with a single 0 index.
598 markIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
602 // Now, iterate all uses of the argument to see if there are any uses that are
603 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
604 SmallVector<LoadInst *, 16> Loads;
605 IndicesVector Operands;
606 for (Use &U : Arg->uses()) {
607 User *UR = U.getUser();
609 if (LoadInst *LI = dyn_cast<LoadInst>(UR)) {
610 // Don't hack volatile/atomic loads
614 // Direct loads are equivalent to a GEP with a zero index and then a load.
615 Operands.push_back(0);
616 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UR)) {
617 if (GEP->use_empty()) {
618 // Dead GEP's cause trouble later. Just remove them if we run into
620 GEP->eraseFromParent();
621 // TODO: This runs the above loop over and over again for dead GEPs
622 // Couldn't we just do increment the UI iterator earlier and erase the
624 return isSafeToPromoteArgument(Arg, isByValOrInAlloca, AAR,
628 // Ensure that all of the indices are constants.
629 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); i != e;
631 if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
632 Operands.push_back(C->getSExtValue());
634 return false; // Not a constant operand GEP!
636 // Ensure that the only users of the GEP are load instructions.
637 for (User *GEPU : GEP->users())
638 if (LoadInst *LI = dyn_cast<LoadInst>(GEPU)) {
639 // Don't hack volatile/atomic loads
644 // Other uses than load?
648 return false; // Not a load or a GEP.
651 // Now, see if it is safe to promote this load / loads of this GEP. Loading
652 // is safe if Operands, or a prefix of Operands, is marked as safe.
653 if (!prefixIn(Operands, SafeToUnconditionallyLoad))
656 // See if we are already promoting a load with these indices. If not, check
657 // to make sure that we aren't promoting too many elements. If so, nothing
659 if (ToPromote.find(Operands) == ToPromote.end()) {
660 if (MaxElements > 0 && ToPromote.size() == MaxElements) {
661 DEBUG(dbgs() << "argpromotion not promoting argument '"
663 << "' because it would require adding more "
664 << "than " << MaxElements
665 << " arguments to the function.\n");
666 // We limit aggregate promotion to only promoting up to a fixed number
667 // of elements of the aggregate.
670 ToPromote.insert(std::move(Operands));
675 return true; // No users, this is a dead argument.
677 // Okay, now we know that the argument is only used by load instructions and
678 // it is safe to unconditionally perform all of them. Use alias analysis to
679 // check to see if the pointer is guaranteed to not be modified from entry of
680 // the function to each of the load instructions.
682 // Because there could be several/many load instructions, remember which
683 // blocks we know to be transparent to the load.
684 df_iterator_default_set<BasicBlock *, 16> TranspBlocks;
686 for (LoadInst *Load : Loads) {
687 // Check to see if the load is invalidated from the start of the block to
689 BasicBlock *BB = Load->getParent();
691 MemoryLocation Loc = MemoryLocation::get(Load);
692 if (AAR.canInstructionRangeModRef(BB->front(), *Load, Loc, MRI_Mod))
693 return false; // Pointer is invalidated!
695 // Now check every path from the entry block to the load for transparency.
696 // To do this, we perform a depth first search on the inverse CFG from the
698 for (BasicBlock *P : predecessors(BB)) {
699 for (BasicBlock *TranspBB : inverse_depth_first_ext(P, TranspBlocks))
700 if (AAR.canBasicBlockModify(*TranspBB, Loc))
705 // If the path from the entry of the function to each load is free of
706 // instructions that potentially invalidate the load, we can make the
711 /// \brief Checks if a type could have padding bytes.
712 static bool isDenselyPacked(Type *type, const DataLayout &DL) {
714 // There is no size information, so be conservative.
715 if (!type->isSized())
718 // If the alloc size is not equal to the storage size, then there are padding
719 // bytes. For x86_fp80 on x86-64, size: 80 alloc size: 128.
720 if (DL.getTypeSizeInBits(type) != DL.getTypeAllocSizeInBits(type))
723 if (!isa<CompositeType>(type))
726 // For homogenous sequential types, check for padding within members.
727 if (SequentialType *seqTy = dyn_cast<SequentialType>(type))
728 return isDenselyPacked(seqTy->getElementType(), DL);
730 // Check for padding within and between elements of a struct.
731 StructType *StructTy = cast<StructType>(type);
732 const StructLayout *Layout = DL.getStructLayout(StructTy);
733 uint64_t StartPos = 0;
734 for (unsigned i = 0, E = StructTy->getNumElements(); i < E; ++i) {
735 Type *ElTy = StructTy->getElementType(i);
736 if (!isDenselyPacked(ElTy, DL))
738 if (StartPos != Layout->getElementOffsetInBits(i))
740 StartPos += DL.getTypeAllocSizeInBits(ElTy);
746 /// \brief Checks if the padding bytes of an argument could be accessed.
747 static bool canPaddingBeAccessed(Argument *arg) {
749 assert(arg->hasByValAttr());
751 // Track all the pointers to the argument to make sure they are not captured.
752 SmallPtrSet<Value *, 16> PtrValues;
753 PtrValues.insert(arg);
755 // Track all of the stores.
756 SmallVector<StoreInst *, 16> Stores;
758 // Scan through the uses recursively to make sure the pointer is always used
760 SmallVector<Value *, 16> WorkList;
761 WorkList.insert(WorkList.end(), arg->user_begin(), arg->user_end());
762 while (!WorkList.empty()) {
763 Value *V = WorkList.back();
765 if (isa<GetElementPtrInst>(V) || isa<PHINode>(V)) {
766 if (PtrValues.insert(V).second)
767 WorkList.insert(WorkList.end(), V->user_begin(), V->user_end());
768 } else if (StoreInst *Store = dyn_cast<StoreInst>(V)) {
769 Stores.push_back(Store);
770 } else if (!isa<LoadInst>(V)) {
775 // Check to make sure the pointers aren't captured
776 for (StoreInst *Store : Stores)
777 if (PtrValues.count(Store->getValueOperand()))
783 /// PromoteArguments - This method checks the specified function to see if there
784 /// are any promotable arguments and if it is safe to promote the function (for
785 /// example, all callers are direct). If safe to promote some arguments, it
786 /// calls the DoPromotion method.
789 promoteArguments(Function *F, function_ref<AAResults &(Function &F)> AARGetter,
790 unsigned MaxElements,
791 Optional<function_ref<void(CallSite OldCS, CallSite NewCS)>>
793 // Make sure that it is local to this module.
794 if (!F->hasLocalLinkage())
797 // Don't promote arguments for variadic functions. Adding, removing, or
798 // changing non-pack parameters can change the classification of pack
799 // parameters. Frontends encode that classification at the call site in the
800 // IR, while in the callee the classification is determined dynamically based
801 // on the number of registers consumed so far.
805 // First check: see if there are any pointer arguments! If not, quick exit.
806 SmallVector<Argument *, 16> PointerArgs;
807 for (Argument &I : F->args())
808 if (I.getType()->isPointerTy())
809 PointerArgs.push_back(&I);
810 if (PointerArgs.empty())
813 // Second check: make sure that all callers are direct callers. We can't
814 // transform functions that have indirect callers. Also see if the function
815 // is self-recursive.
816 bool isSelfRecursive = false;
817 for (Use &U : F->uses()) {
818 CallSite CS(U.getUser());
819 // Must be a direct call.
820 if (CS.getInstruction() == nullptr || !CS.isCallee(&U))
823 if (CS.getInstruction()->getParent()->getParent() == F)
824 isSelfRecursive = true;
827 const DataLayout &DL = F->getParent()->getDataLayout();
829 AAResults &AAR = AARGetter(*F);
831 // Check to see which arguments are promotable. If an argument is promotable,
832 // add it to ArgsToPromote.
833 SmallPtrSet<Argument *, 8> ArgsToPromote;
834 SmallPtrSet<Argument *, 8> ByValArgsToTransform;
835 for (Argument *PtrArg : PointerArgs) {
836 Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
838 // Replace sret attribute with noalias. This reduces register pressure by
839 // avoiding a register copy.
840 if (PtrArg->hasStructRetAttr()) {
841 unsigned ArgNo = PtrArg->getArgNo();
842 F->removeParamAttr(ArgNo, Attribute::StructRet);
843 F->addParamAttr(ArgNo, Attribute::NoAlias);
844 for (Use &U : F->uses()) {
845 CallSite CS(U.getUser());
846 CS.removeParamAttr(ArgNo, Attribute::StructRet);
847 CS.addParamAttr(ArgNo, Attribute::NoAlias);
851 // If this is a byval argument, and if the aggregate type is small, just
852 // pass the elements, which is always safe, if the passed value is densely
853 // packed or if we can prove the padding bytes are never accessed. This does
854 // not apply to inalloca.
855 bool isSafeToPromote =
856 PtrArg->hasByValAttr() &&
857 (isDenselyPacked(AgTy, DL) || !canPaddingBeAccessed(PtrArg));
858 if (isSafeToPromote) {
859 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
860 if (MaxElements > 0 && STy->getNumElements() > MaxElements) {
861 DEBUG(dbgs() << "argpromotion disable promoting argument '"
863 << "' because it would require adding more"
864 << " than " << MaxElements
865 << " arguments to the function.\n");
869 // If all the elements are single-value types, we can promote it.
870 bool AllSimple = true;
871 for (const auto *EltTy : STy->elements()) {
872 if (!EltTy->isSingleValueType()) {
878 // Safe to transform, don't even bother trying to "promote" it.
879 // Passing the elements as a scalar will allow sroa to hack on
880 // the new alloca we introduce.
882 ByValArgsToTransform.insert(PtrArg);
888 // If the argument is a recursive type and we're in a recursive
889 // function, we could end up infinitely peeling the function argument.
890 if (isSelfRecursive) {
891 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
892 bool RecursiveType = false;
893 for (const auto *EltTy : STy->elements()) {
894 if (EltTy == PtrArg->getType()) {
895 RecursiveType = true;
904 // Otherwise, see if we can promote the pointer to its value.
905 if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValOrInAllocaAttr(), AAR,
907 ArgsToPromote.insert(PtrArg);
910 // No promotable pointer arguments.
911 if (ArgsToPromote.empty() && ByValArgsToTransform.empty())
914 return doPromotion(F, ArgsToPromote, ByValArgsToTransform, ReplaceCallSite);
917 PreservedAnalyses ArgumentPromotionPass::run(LazyCallGraph::SCC &C,
918 CGSCCAnalysisManager &AM,
920 CGSCCUpdateResult &UR) {
921 bool Changed = false, LocalChange;
923 // Iterate until we stop promoting from this SCC.
927 for (LazyCallGraph::Node &N : C) {
928 Function &OldF = N.getFunction();
930 FunctionAnalysisManager &FAM =
931 AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, CG).getManager();
932 // FIXME: This lambda must only be used with this function. We should
933 // skip the lambda and just get the AA results directly.
934 auto AARGetter = [&](Function &F) -> AAResults & {
935 assert(&F == &OldF && "Called with an unexpected function!");
936 return FAM.getResult<AAManager>(F);
939 Function *NewF = promoteArguments(&OldF, AARGetter, 3u, None);
944 // Directly substitute the functions in the call graph. Note that this
945 // requires the old function to be completely dead and completely
946 // replaced by the new function. It does no call graph updates, it merely
947 // swaps out the particular function mapped to a particular node in the
949 C.getOuterRefSCC().replaceNodeFunction(N, *NewF);
950 OldF.eraseFromParent();
953 Changed |= LocalChange;
954 } while (LocalChange);
957 return PreservedAnalyses::all();
959 return PreservedAnalyses::none();
963 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
965 struct ArgPromotion : public CallGraphSCCPass {
966 void getAnalysisUsage(AnalysisUsage &AU) const override {
967 AU.addRequired<AssumptionCacheTracker>();
968 AU.addRequired<TargetLibraryInfoWrapperPass>();
969 getAAResultsAnalysisUsage(AU);
970 CallGraphSCCPass::getAnalysisUsage(AU);
973 bool runOnSCC(CallGraphSCC &SCC) override;
974 static char ID; // Pass identification, replacement for typeid
975 explicit ArgPromotion(unsigned MaxElements = 3)
976 : CallGraphSCCPass(ID), MaxElements(MaxElements) {
977 initializeArgPromotionPass(*PassRegistry::getPassRegistry());
981 using llvm::Pass::doInitialization;
982 bool doInitialization(CallGraph &CG) override;
983 /// The maximum number of elements to expand, or 0 for unlimited.
984 unsigned MaxElements;
988 char ArgPromotion::ID = 0;
989 INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion",
990 "Promote 'by reference' arguments to scalars", false,
992 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
993 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
994 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
995 INITIALIZE_PASS_END(ArgPromotion, "argpromotion",
996 "Promote 'by reference' arguments to scalars", false, false)
998 Pass *llvm::createArgumentPromotionPass(unsigned MaxElements) {
999 return new ArgPromotion(MaxElements);
1002 bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) {
1006 // Get the callgraph information that we need to update to reflect our
1008 CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
1010 LegacyAARGetter AARGetter(*this);
1012 bool Changed = false, LocalChange;
1014 // Iterate until we stop promoting from this SCC.
1016 LocalChange = false;
1017 // Attempt to promote arguments from all functions in this SCC.
1018 for (CallGraphNode *OldNode : SCC) {
1019 Function *OldF = OldNode->getFunction();
1023 auto ReplaceCallSite = [&](CallSite OldCS, CallSite NewCS) {
1024 Function *Caller = OldCS.getInstruction()->getParent()->getParent();
1025 CallGraphNode *NewCalleeNode =
1026 CG.getOrInsertFunction(NewCS.getCalledFunction());
1027 CallGraphNode *CallerNode = CG[Caller];
1028 CallerNode->replaceCallEdge(OldCS, NewCS, NewCalleeNode);
1031 if (Function *NewF = promoteArguments(OldF, AARGetter, MaxElements,
1032 {ReplaceCallSite})) {
1035 // Update the call graph for the newly promoted function.
1036 CallGraphNode *NewNode = CG.getOrInsertFunction(NewF);
1037 NewNode->stealCalledFunctionsFrom(OldNode);
1038 if (OldNode->getNumReferences() == 0)
1039 delete CG.removeFunctionFromModule(OldNode);
1041 OldF->setLinkage(Function::ExternalLinkage);
1043 // And updat ethe SCC we're iterating as well.
1044 SCC.ReplaceNode(OldNode, NewNode);
1047 // Remember that we changed something.
1048 Changed |= LocalChange;
1049 } while (LocalChange);
1054 bool ArgPromotion::doInitialization(CallGraph &CG) {
1055 return CallGraphSCCPass::doInitialization(CG);