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/None.h"
35 #include "llvm/ADT/Optional.h"
36 #include "llvm/ADT/STLExtras.h"
37 #include "llvm/ADT/SmallPtrSet.h"
38 #include "llvm/ADT/SmallVector.h"
39 #include "llvm/ADT/Statistic.h"
40 #include "llvm/ADT/StringExtras.h"
41 #include "llvm/ADT/Twine.h"
42 #include "llvm/Analysis/AliasAnalysis.h"
43 #include "llvm/Analysis/AssumptionCache.h"
44 #include "llvm/Analysis/BasicAliasAnalysis.h"
45 #include "llvm/Analysis/CGSCCPassManager.h"
46 #include "llvm/Analysis/CallGraph.h"
47 #include "llvm/Analysis/CallGraphSCCPass.h"
48 #include "llvm/Analysis/LazyCallGraph.h"
49 #include "llvm/Analysis/Loads.h"
50 #include "llvm/Analysis/MemoryLocation.h"
51 #include "llvm/Analysis/TargetLibraryInfo.h"
52 #include "llvm/Analysis/TargetTransformInfo.h"
53 #include "llvm/IR/Argument.h"
54 #include "llvm/IR/Attributes.h"
55 #include "llvm/IR/BasicBlock.h"
56 #include "llvm/IR/CFG.h"
57 #include "llvm/IR/CallSite.h"
58 #include "llvm/IR/Constants.h"
59 #include "llvm/IR/DataLayout.h"
60 #include "llvm/IR/DerivedTypes.h"
61 #include "llvm/IR/Function.h"
62 #include "llvm/IR/InstrTypes.h"
63 #include "llvm/IR/Instruction.h"
64 #include "llvm/IR/Instructions.h"
65 #include "llvm/IR/Metadata.h"
66 #include "llvm/IR/Module.h"
67 #include "llvm/IR/PassManager.h"
68 #include "llvm/IR/Type.h"
69 #include "llvm/IR/Use.h"
70 #include "llvm/IR/User.h"
71 #include "llvm/IR/Value.h"
72 #include "llvm/Pass.h"
73 #include "llvm/Support/Casting.h"
74 #include "llvm/Support/Debug.h"
75 #include "llvm/Support/raw_ostream.h"
76 #include "llvm/Transforms/IPO.h"
90 #define DEBUG_TYPE "argpromotion"
92 STATISTIC(NumArgumentsPromoted, "Number of pointer arguments promoted");
93 STATISTIC(NumAggregatesPromoted, "Number of aggregate arguments promoted");
94 STATISTIC(NumByValArgsPromoted, "Number of byval arguments promoted");
95 STATISTIC(NumArgumentsDead, "Number of dead pointer args eliminated");
97 /// A vector used to hold the indices of a single GEP instruction
98 using IndicesVector = std::vector<uint64_t>;
100 /// DoPromotion - This method actually performs the promotion of the specified
101 /// arguments, and returns the new function. At this point, we know that it's
104 doPromotion(Function *F, SmallPtrSetImpl<Argument *> &ArgsToPromote,
105 SmallPtrSetImpl<Argument *> &ByValArgsToTransform,
106 Optional<function_ref<void(CallSite OldCS, CallSite NewCS)>>
108 // Start by computing a new prototype for the function, which is the same as
109 // the old function, but has modified arguments.
110 FunctionType *FTy = F->getFunctionType();
111 std::vector<Type *> Params;
113 using ScalarizeTable = std::set<std::pair<Type *, IndicesVector>>;
115 // ScalarizedElements - If we are promoting a pointer that has elements
116 // accessed out of it, keep track of which elements are accessed so that we
117 // can add one argument for each.
119 // Arguments that are directly loaded will have a zero element value here, to
120 // handle cases where there are both a direct load and GEP accesses.
121 std::map<Argument *, ScalarizeTable> ScalarizedElements;
123 // OriginalLoads - Keep track of a representative load instruction from the
124 // original function so that we can tell the alias analysis implementation
125 // what the new GEP/Load instructions we are inserting look like.
126 // We need to keep the original loads for each argument and the elements
127 // of the argument that are accessed.
128 std::map<std::pair<Argument *, IndicesVector>, LoadInst *> OriginalLoads;
130 // Attribute - Keep track of the parameter attributes for the arguments
131 // that we are *not* promoting. For the ones that we do promote, the parameter
132 // attributes are lost
133 SmallVector<AttributeSet, 8> ArgAttrVec;
134 AttributeList PAL = F->getAttributes();
136 // First, determine the new argument list
138 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
140 if (ByValArgsToTransform.count(&*I)) {
141 // Simple byval argument? Just add all the struct element types.
142 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
143 StructType *STy = cast<StructType>(AgTy);
144 Params.insert(Params.end(), STy->element_begin(), STy->element_end());
145 ArgAttrVec.insert(ArgAttrVec.end(), STy->getNumElements(),
147 ++NumByValArgsPromoted;
148 } else if (!ArgsToPromote.count(&*I)) {
149 // Unchanged argument
150 Params.push_back(I->getType());
151 ArgAttrVec.push_back(PAL.getParamAttributes(ArgNo));
152 } else if (I->use_empty()) {
153 // Dead argument (which are always marked as promotable)
156 // There may be remaining metadata uses of the argument for things like
157 // llvm.dbg.value. Replace them with undef.
158 I->replaceAllUsesWith(UndefValue::get(I->getType()));
160 // Okay, this is being promoted. This means that the only uses are loads
161 // or GEPs which are only used by loads
163 // In this table, we will track which indices are loaded from the argument
164 // (where direct loads are tracked as no indices).
165 ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
166 for (User *U : I->users()) {
167 Instruction *UI = cast<Instruction>(U);
169 if (LoadInst *L = dyn_cast<LoadInst>(UI))
170 SrcTy = L->getType();
172 SrcTy = cast<GetElementPtrInst>(UI)->getSourceElementType();
173 IndicesVector Indices;
174 Indices.reserve(UI->getNumOperands() - 1);
175 // Since loads will only have a single operand, and GEPs only a single
176 // non-index operand, this will record direct loads without any indices,
177 // and gep+loads with the GEP indices.
178 for (User::op_iterator II = UI->op_begin() + 1, IE = UI->op_end();
180 Indices.push_back(cast<ConstantInt>(*II)->getSExtValue());
181 // GEPs with a single 0 index can be merged with direct loads
182 if (Indices.size() == 1 && Indices.front() == 0)
184 ArgIndices.insert(std::make_pair(SrcTy, Indices));
186 if (LoadInst *L = dyn_cast<LoadInst>(UI))
189 // Take any load, we will use it only to update Alias Analysis
190 OrigLoad = cast<LoadInst>(UI->user_back());
191 OriginalLoads[std::make_pair(&*I, Indices)] = OrigLoad;
194 // Add a parameter to the function for each element passed in.
195 for (const auto &ArgIndex : ArgIndices) {
196 // not allowed to dereference ->begin() if size() is 0
197 Params.push_back(GetElementPtrInst::getIndexedType(
198 cast<PointerType>(I->getType()->getScalarType())->getElementType(),
200 ArgAttrVec.push_back(AttributeSet());
201 assert(Params.back());
204 if (ArgIndices.size() == 1 && ArgIndices.begin()->second.empty())
205 ++NumArgumentsPromoted;
207 ++NumAggregatesPromoted;
211 Type *RetTy = FTy->getReturnType();
213 // Construct the new function type using the new arguments.
214 FunctionType *NFTy = FunctionType::get(RetTy, Params, FTy->isVarArg());
216 // Create the new function body and insert it into the module.
217 Function *NF = Function::Create(NFTy, F->getLinkage(), F->getAddressSpace(),
219 NF->copyAttributesFrom(F);
221 // Patch the pointer to LLVM function in debug info descriptor.
222 NF->setSubprogram(F->getSubprogram());
223 F->setSubprogram(nullptr);
225 LLVM_DEBUG(dbgs() << "ARG PROMOTION: Promoting to:" << *NF << "\n"
228 // Recompute the parameter attributes list based on the new arguments for
230 NF->setAttributes(AttributeList::get(F->getContext(), PAL.getFnAttributes(),
231 PAL.getRetAttributes(), ArgAttrVec));
234 F->getParent()->getFunctionList().insert(F->getIterator(), NF);
237 // Loop over all of the callers of the function, transforming the call sites
238 // to pass in the loaded pointers.
240 SmallVector<Value *, 16> Args;
241 while (!F->use_empty()) {
242 CallSite CS(F->user_back());
243 assert(CS.getCalledFunction() == F);
244 Instruction *Call = CS.getInstruction();
245 const AttributeList &CallPAL = CS.getAttributes();
247 // Loop over the operands, inserting GEP and loads in the caller as
249 CallSite::arg_iterator AI = CS.arg_begin();
251 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(); I != E;
253 if (!ArgsToPromote.count(&*I) && !ByValArgsToTransform.count(&*I)) {
254 Args.push_back(*AI); // Unmodified argument
255 ArgAttrVec.push_back(CallPAL.getParamAttributes(ArgNo));
256 } else if (ByValArgsToTransform.count(&*I)) {
257 // Emit a GEP and load for each element of the struct.
258 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
259 StructType *STy = cast<StructType>(AgTy);
261 ConstantInt::get(Type::getInt32Ty(F->getContext()), 0), nullptr};
262 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
263 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
264 Value *Idx = GetElementPtrInst::Create(
265 STy, *AI, Idxs, (*AI)->getName() + "." + Twine(i), Call);
266 // TODO: Tell AA about the new values?
267 Args.push_back(new LoadInst(Idx, Idx->getName() + ".val", Call));
268 ArgAttrVec.push_back(AttributeSet());
270 } else if (!I->use_empty()) {
271 // Non-dead argument: insert GEPs and loads as appropriate.
272 ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
273 // Store the Value* version of the indices in here, but declare it now
275 std::vector<Value *> Ops;
276 for (const auto &ArgIndex : ArgIndices) {
279 OriginalLoads[std::make_pair(&*I, ArgIndex.second)];
280 if (!ArgIndex.second.empty()) {
281 Ops.reserve(ArgIndex.second.size());
282 Type *ElTy = V->getType();
283 for (auto II : ArgIndex.second) {
284 // Use i32 to index structs, and i64 for others (pointers/arrays).
285 // This satisfies GEP constraints.
287 (ElTy->isStructTy() ? Type::getInt32Ty(F->getContext())
288 : Type::getInt64Ty(F->getContext()));
289 Ops.push_back(ConstantInt::get(IdxTy, II));
290 // Keep track of the type we're currently indexing.
291 if (auto *ElPTy = dyn_cast<PointerType>(ElTy))
292 ElTy = ElPTy->getElementType();
294 ElTy = cast<CompositeType>(ElTy)->getTypeAtIndex(II);
296 // And create a GEP to extract those indices.
297 V = GetElementPtrInst::Create(ArgIndex.first, V, Ops,
298 V->getName() + ".idx", Call);
301 // Since we're replacing a load make sure we take the alignment
302 // of the previous load.
303 LoadInst *newLoad = new LoadInst(V, V->getName() + ".val", Call);
304 newLoad->setAlignment(OrigLoad->getAlignment());
305 // Transfer the AA info too.
307 OrigLoad->getAAMetadata(AAInfo);
308 newLoad->setAAMetadata(AAInfo);
310 Args.push_back(newLoad);
311 ArgAttrVec.push_back(AttributeSet());
315 // Push any varargs arguments on the list.
316 for (; AI != CS.arg_end(); ++AI, ++ArgNo) {
318 ArgAttrVec.push_back(CallPAL.getParamAttributes(ArgNo));
321 SmallVector<OperandBundleDef, 1> OpBundles;
322 CS.getOperandBundlesAsDefs(OpBundles);
325 if (InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
326 NewCS = InvokeInst::Create(NF, II->getNormalDest(), II->getUnwindDest(),
327 Args, OpBundles, "", Call);
329 auto *NewCall = CallInst::Create(NF, Args, OpBundles, "", Call);
330 NewCall->setTailCallKind(cast<CallInst>(Call)->getTailCallKind());
333 NewCS.setCallingConv(CS.getCallingConv());
335 AttributeList::get(F->getContext(), CallPAL.getFnAttributes(),
336 CallPAL.getRetAttributes(), ArgAttrVec));
337 NewCS->setDebugLoc(Call->getDebugLoc());
339 if (Call->extractProfTotalWeight(W))
340 NewCS->setProfWeight(W);
344 // Update the callgraph to know that the callsite has been transformed.
346 (*ReplaceCallSite)(CS, NewCS);
348 if (!Call->use_empty()) {
349 Call->replaceAllUsesWith(NewCS.getInstruction());
350 NewCS->takeName(Call);
353 // Finally, remove the old call from the program, reducing the use-count of
355 Call->eraseFromParent();
358 const DataLayout &DL = F->getParent()->getDataLayout();
360 // Since we have now created the new function, splice the body of the old
361 // function right into the new function, leaving the old rotting hulk of the
363 NF->getBasicBlockList().splice(NF->begin(), F->getBasicBlockList());
365 // Loop over the argument list, transferring uses of the old arguments over to
366 // the new arguments, also transferring over the names as well.
367 for (Function::arg_iterator I = F->arg_begin(), E = F->arg_end(),
368 I2 = NF->arg_begin();
370 if (!ArgsToPromote.count(&*I) && !ByValArgsToTransform.count(&*I)) {
371 // If this is an unmodified argument, move the name and users over to the
373 I->replaceAllUsesWith(&*I2);
379 if (ByValArgsToTransform.count(&*I)) {
380 // In the callee, we create an alloca, and store each of the new incoming
381 // arguments into the alloca.
382 Instruction *InsertPt = &NF->begin()->front();
384 // Just add all the struct element types.
385 Type *AgTy = cast<PointerType>(I->getType())->getElementType();
386 Value *TheAlloca = new AllocaInst(AgTy, DL.getAllocaAddrSpace(), nullptr,
387 I->getParamAlignment(), "", InsertPt);
388 StructType *STy = cast<StructType>(AgTy);
389 Value *Idxs[2] = {ConstantInt::get(Type::getInt32Ty(F->getContext()), 0),
392 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
393 Idxs[1] = ConstantInt::get(Type::getInt32Ty(F->getContext()), i);
394 Value *Idx = GetElementPtrInst::Create(
395 AgTy, TheAlloca, Idxs, TheAlloca->getName() + "." + Twine(i),
397 I2->setName(I->getName() + "." + Twine(i));
398 new StoreInst(&*I2++, Idx, InsertPt);
401 // Anything that used the arg should now use the alloca.
402 I->replaceAllUsesWith(TheAlloca);
403 TheAlloca->takeName(&*I);
405 // If the alloca is used in a call, we must clear the tail flag since
406 // the callee now uses an alloca from the caller.
407 for (User *U : TheAlloca->users()) {
408 CallInst *Call = dyn_cast<CallInst>(U);
411 Call->setTailCall(false);
419 // Otherwise, if we promoted this argument, then all users are load
420 // instructions (or GEPs with only load users), and all loads should be
421 // using the new argument that we added.
422 ScalarizeTable &ArgIndices = ScalarizedElements[&*I];
424 while (!I->use_empty()) {
425 if (LoadInst *LI = dyn_cast<LoadInst>(I->user_back())) {
426 assert(ArgIndices.begin()->second.empty() &&
427 "Load element should sort to front!");
428 I2->setName(I->getName() + ".val");
429 LI->replaceAllUsesWith(&*I2);
430 LI->eraseFromParent();
431 LLVM_DEBUG(dbgs() << "*** Promoted load of argument '" << I->getName()
432 << "' in function '" << F->getName() << "'\n");
434 GetElementPtrInst *GEP = cast<GetElementPtrInst>(I->user_back());
435 IndicesVector Operands;
436 Operands.reserve(GEP->getNumIndices());
437 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
439 Operands.push_back(cast<ConstantInt>(*II)->getSExtValue());
441 // GEPs with a single 0 index can be merged with direct loads
442 if (Operands.size() == 1 && Operands.front() == 0)
445 Function::arg_iterator TheArg = I2;
446 for (ScalarizeTable::iterator It = ArgIndices.begin();
447 It->second != Operands; ++It, ++TheArg) {
448 assert(It != ArgIndices.end() && "GEP not handled??");
451 std::string NewName = I->getName();
452 for (unsigned i = 0, e = Operands.size(); i != e; ++i) {
453 NewName += "." + utostr(Operands[i]);
456 TheArg->setName(NewName);
458 LLVM_DEBUG(dbgs() << "*** Promoted agg argument '" << TheArg->getName()
459 << "' of function '" << NF->getName() << "'\n");
461 // All of the uses must be load instructions. Replace them all with
462 // the argument specified by ArgNo.
463 while (!GEP->use_empty()) {
464 LoadInst *L = cast<LoadInst>(GEP->user_back());
465 L->replaceAllUsesWith(&*TheArg);
466 L->eraseFromParent();
468 GEP->eraseFromParent();
472 // Increment I2 past all of the arguments added for this promoted pointer.
473 std::advance(I2, ArgIndices.size());
479 /// AllCallersPassInValidPointerForArgument - Return true if we can prove that
480 /// all callees pass in a valid pointer for the specified function argument.
481 static bool allCallersPassInValidPointerForArgument(Argument *Arg) {
482 Function *Callee = Arg->getParent();
483 const DataLayout &DL = Callee->getParent()->getDataLayout();
485 unsigned ArgNo = Arg->getArgNo();
487 // Look at all call sites of the function. At this point we know we only have
489 for (User *U : Callee->users()) {
491 assert(CS && "Should only have direct calls!");
493 if (!isDereferenceablePointer(CS.getArgument(ArgNo), DL))
499 /// Returns true if Prefix is a prefix of longer. That means, Longer has a size
500 /// that is greater than or equal to the size of prefix, and each of the
501 /// elements in Prefix is the same as the corresponding elements in Longer.
503 /// This means it also returns true when Prefix and Longer are equal!
504 static bool isPrefix(const IndicesVector &Prefix, const IndicesVector &Longer) {
505 if (Prefix.size() > Longer.size())
507 return std::equal(Prefix.begin(), Prefix.end(), Longer.begin());
510 /// Checks if Indices, or a prefix of Indices, is in Set.
511 static bool prefixIn(const IndicesVector &Indices,
512 std::set<IndicesVector> &Set) {
513 std::set<IndicesVector>::iterator Low;
514 Low = Set.upper_bound(Indices);
515 if (Low != Set.begin())
517 // Low is now the last element smaller than or equal to Indices. This means
518 // it points to a prefix of Indices (possibly Indices itself), if such
521 // This load is safe if any prefix of its operands is safe to load.
522 return Low != Set.end() && isPrefix(*Low, Indices);
525 /// Mark the given indices (ToMark) as safe in the given set of indices
526 /// (Safe). Marking safe usually means adding ToMark to Safe. However, if there
527 /// is already a prefix of Indices in Safe, Indices are implicitely marked safe
528 /// already. Furthermore, any indices that Indices is itself a prefix of, are
529 /// removed from Safe (since they are implicitely safe because of Indices now).
530 static void markIndicesSafe(const IndicesVector &ToMark,
531 std::set<IndicesVector> &Safe) {
532 std::set<IndicesVector>::iterator Low;
533 Low = Safe.upper_bound(ToMark);
534 // Guard against the case where Safe is empty
535 if (Low != Safe.begin())
537 // Low is now the last element smaller than or equal to Indices. This
538 // means it points to a prefix of Indices (possibly Indices itself), if
539 // such prefix exists.
540 if (Low != Safe.end()) {
541 if (isPrefix(*Low, ToMark))
542 // If there is already a prefix of these indices (or exactly these
543 // indices) marked a safe, don't bother adding these indices
546 // Increment Low, so we can use it as a "insert before" hint
550 Low = Safe.insert(Low, ToMark);
552 // If there we're a prefix of longer index list(s), remove those
553 std::set<IndicesVector>::iterator End = Safe.end();
554 while (Low != End && isPrefix(ToMark, *Low)) {
555 std::set<IndicesVector>::iterator Remove = Low;
561 /// isSafeToPromoteArgument - As you might guess from the name of this method,
562 /// it checks to see if it is both safe and useful to promote the argument.
563 /// This method limits promotion of aggregates to only promote up to three
564 /// elements of the aggregate in order to avoid exploding the number of
565 /// arguments passed in.
566 static bool isSafeToPromoteArgument(Argument *Arg, bool isByValOrInAlloca,
567 AAResults &AAR, unsigned MaxElements) {
568 using GEPIndicesSet = std::set<IndicesVector>;
570 // Quick exit for unused arguments
571 if (Arg->use_empty())
574 // We can only promote this argument if all of the uses are loads, or are GEP
575 // instructions (with constant indices) that are subsequently loaded.
577 // Promoting the argument causes it to be loaded in the caller
578 // unconditionally. This is only safe if we can prove that either the load
579 // would have happened in the callee anyway (ie, there is a load in the entry
580 // block) or the pointer passed in at every call site is guaranteed to be
582 // In the former case, invalid loads can happen, but would have happened
583 // anyway, in the latter case, invalid loads won't happen. This prevents us
584 // from introducing an invalid load that wouldn't have happened in the
587 // This set will contain all sets of indices that are loaded in the entry
588 // block, and thus are safe to unconditionally load in the caller.
590 // This optimization is also safe for InAlloca parameters, because it verifies
591 // that the address isn't captured.
592 GEPIndicesSet SafeToUnconditionallyLoad;
594 // This set contains all the sets of indices that we are planning to promote.
595 // This makes it possible to limit the number of arguments added.
596 GEPIndicesSet ToPromote;
598 // If the pointer is always valid, any load with first index 0 is valid.
599 if (isByValOrInAlloca || allCallersPassInValidPointerForArgument(Arg))
600 SafeToUnconditionallyLoad.insert(IndicesVector(1, 0));
602 // First, iterate the entry block and mark loads of (geps of) arguments as
604 BasicBlock &EntryBlock = Arg->getParent()->front();
605 // Declare this here so we can reuse it
606 IndicesVector Indices;
607 for (Instruction &I : EntryBlock)
608 if (LoadInst *LI = dyn_cast<LoadInst>(&I)) {
609 Value *V = LI->getPointerOperand();
610 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
611 V = GEP->getPointerOperand();
613 // This load actually loads (part of) Arg? Check the indices then.
614 Indices.reserve(GEP->getNumIndices());
615 for (User::op_iterator II = GEP->idx_begin(), IE = GEP->idx_end();
617 if (ConstantInt *CI = dyn_cast<ConstantInt>(*II))
618 Indices.push_back(CI->getSExtValue());
620 // We found a non-constant GEP index for this argument? Bail out
621 // right away, can't promote this argument at all.
624 // Indices checked out, mark them as safe
625 markIndicesSafe(Indices, SafeToUnconditionallyLoad);
628 } else if (V == Arg) {
629 // Direct loads are equivalent to a GEP with a single 0 index.
630 markIndicesSafe(IndicesVector(1, 0), SafeToUnconditionallyLoad);
634 // Now, iterate all uses of the argument to see if there are any uses that are
635 // not (GEP+)loads, or any (GEP+)loads that are not safe to promote.
636 SmallVector<LoadInst *, 16> Loads;
637 IndicesVector Operands;
638 for (Use &U : Arg->uses()) {
639 User *UR = U.getUser();
641 if (LoadInst *LI = dyn_cast<LoadInst>(UR)) {
642 // Don't hack volatile/atomic loads
646 // Direct loads are equivalent to a GEP with a zero index and then a load.
647 Operands.push_back(0);
648 } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(UR)) {
649 if (GEP->use_empty()) {
650 // Dead GEP's cause trouble later. Just remove them if we run into
652 GEP->eraseFromParent();
653 // TODO: This runs the above loop over and over again for dead GEPs
654 // Couldn't we just do increment the UI iterator earlier and erase the
656 return isSafeToPromoteArgument(Arg, isByValOrInAlloca, AAR,
660 // Ensure that all of the indices are constants.
661 for (User::op_iterator i = GEP->idx_begin(), e = GEP->idx_end(); i != e;
663 if (ConstantInt *C = dyn_cast<ConstantInt>(*i))
664 Operands.push_back(C->getSExtValue());
666 return false; // Not a constant operand GEP!
668 // Ensure that the only users of the GEP are load instructions.
669 for (User *GEPU : GEP->users())
670 if (LoadInst *LI = dyn_cast<LoadInst>(GEPU)) {
671 // Don't hack volatile/atomic loads
676 // Other uses than load?
680 return false; // Not a load or a GEP.
683 // Now, see if it is safe to promote this load / loads of this GEP. Loading
684 // is safe if Operands, or a prefix of Operands, is marked as safe.
685 if (!prefixIn(Operands, SafeToUnconditionallyLoad))
688 // See if we are already promoting a load with these indices. If not, check
689 // to make sure that we aren't promoting too many elements. If so, nothing
691 if (ToPromote.find(Operands) == ToPromote.end()) {
692 if (MaxElements > 0 && ToPromote.size() == MaxElements) {
693 LLVM_DEBUG(dbgs() << "argpromotion not promoting argument '"
695 << "' because it would require adding more "
696 << "than " << MaxElements
697 << " arguments to the function.\n");
698 // We limit aggregate promotion to only promoting up to a fixed number
699 // of elements of the aggregate.
702 ToPromote.insert(std::move(Operands));
707 return true; // No users, this is a dead argument.
709 // Okay, now we know that the argument is only used by load instructions and
710 // it is safe to unconditionally perform all of them. Use alias analysis to
711 // check to see if the pointer is guaranteed to not be modified from entry of
712 // the function to each of the load instructions.
714 // Because there could be several/many load instructions, remember which
715 // blocks we know to be transparent to the load.
716 df_iterator_default_set<BasicBlock *, 16> TranspBlocks;
718 for (LoadInst *Load : Loads) {
719 // Check to see if the load is invalidated from the start of the block to
721 BasicBlock *BB = Load->getParent();
723 MemoryLocation Loc = MemoryLocation::get(Load);
724 if (AAR.canInstructionRangeModRef(BB->front(), *Load, Loc, ModRefInfo::Mod))
725 return false; // Pointer is invalidated!
727 // Now check every path from the entry block to the load for transparency.
728 // To do this, we perform a depth first search on the inverse CFG from the
730 for (BasicBlock *P : predecessors(BB)) {
731 for (BasicBlock *TranspBB : inverse_depth_first_ext(P, TranspBlocks))
732 if (AAR.canBasicBlockModify(*TranspBB, Loc))
737 // If the path from the entry of the function to each load is free of
738 // instructions that potentially invalidate the load, we can make the
743 /// Checks if a type could have padding bytes.
744 static bool isDenselyPacked(Type *type, const DataLayout &DL) {
745 // There is no size information, so be conservative.
746 if (!type->isSized())
749 // If the alloc size is not equal to the storage size, then there are padding
750 // bytes. For x86_fp80 on x86-64, size: 80 alloc size: 128.
751 if (DL.getTypeSizeInBits(type) != DL.getTypeAllocSizeInBits(type))
754 if (!isa<CompositeType>(type))
757 // For homogenous sequential types, check for padding within members.
758 if (SequentialType *seqTy = dyn_cast<SequentialType>(type))
759 return isDenselyPacked(seqTy->getElementType(), DL);
761 // Check for padding within and between elements of a struct.
762 StructType *StructTy = cast<StructType>(type);
763 const StructLayout *Layout = DL.getStructLayout(StructTy);
764 uint64_t StartPos = 0;
765 for (unsigned i = 0, E = StructTy->getNumElements(); i < E; ++i) {
766 Type *ElTy = StructTy->getElementType(i);
767 if (!isDenselyPacked(ElTy, DL))
769 if (StartPos != Layout->getElementOffsetInBits(i))
771 StartPos += DL.getTypeAllocSizeInBits(ElTy);
777 /// Checks if the padding bytes of an argument could be accessed.
778 static bool canPaddingBeAccessed(Argument *arg) {
779 assert(arg->hasByValAttr());
781 // Track all the pointers to the argument to make sure they are not captured.
782 SmallPtrSet<Value *, 16> PtrValues;
783 PtrValues.insert(arg);
785 // Track all of the stores.
786 SmallVector<StoreInst *, 16> Stores;
788 // Scan through the uses recursively to make sure the pointer is always used
790 SmallVector<Value *, 16> WorkList;
791 WorkList.insert(WorkList.end(), arg->user_begin(), arg->user_end());
792 while (!WorkList.empty()) {
793 Value *V = WorkList.back();
795 if (isa<GetElementPtrInst>(V) || isa<PHINode>(V)) {
796 if (PtrValues.insert(V).second)
797 WorkList.insert(WorkList.end(), V->user_begin(), V->user_end());
798 } else if (StoreInst *Store = dyn_cast<StoreInst>(V)) {
799 Stores.push_back(Store);
800 } else if (!isa<LoadInst>(V)) {
805 // Check to make sure the pointers aren't captured
806 for (StoreInst *Store : Stores)
807 if (PtrValues.count(Store->getValueOperand()))
813 static bool areFunctionArgsABICompatible(
814 const Function &F, const TargetTransformInfo &TTI,
815 SmallPtrSetImpl<Argument *> &ArgsToPromote,
816 SmallPtrSetImpl<Argument *> &ByValArgsToTransform) {
817 for (const Use &U : F.uses()) {
818 CallSite CS(U.getUser());
819 const Function *Caller = CS.getCaller();
820 const Function *Callee = CS.getCalledFunction();
821 if (!TTI.areFunctionArgsABICompatible(Caller, Callee, ArgsToPromote) ||
822 !TTI.areFunctionArgsABICompatible(Caller, Callee, ByValArgsToTransform))
828 /// PromoteArguments - This method checks the specified function to see if there
829 /// are any promotable arguments and if it is safe to promote the function (for
830 /// example, all callers are direct). If safe to promote some arguments, it
831 /// calls the DoPromotion method.
833 promoteArguments(Function *F, function_ref<AAResults &(Function &F)> AARGetter,
834 unsigned MaxElements,
835 Optional<function_ref<void(CallSite OldCS, CallSite NewCS)>>
837 const TargetTransformInfo &TTI) {
838 // Don't perform argument promotion for naked functions; otherwise we can end
839 // up removing parameters that are seemingly 'not used' as they are referred
840 // to in the assembly.
841 if(F->hasFnAttribute(Attribute::Naked))
844 // Make sure that it is local to this module.
845 if (!F->hasLocalLinkage())
848 // Don't promote arguments for variadic functions. Adding, removing, or
849 // changing non-pack parameters can change the classification of pack
850 // parameters. Frontends encode that classification at the call site in the
851 // IR, while in the callee the classification is determined dynamically based
852 // on the number of registers consumed so far.
856 // First check: see if there are any pointer arguments! If not, quick exit.
857 SmallVector<Argument *, 16> PointerArgs;
858 for (Argument &I : F->args())
859 if (I.getType()->isPointerTy())
860 PointerArgs.push_back(&I);
861 if (PointerArgs.empty())
864 // Second check: make sure that all callers are direct callers. We can't
865 // transform functions that have indirect callers. Also see if the function
866 // is self-recursive and check that target features are compatible.
867 bool isSelfRecursive = false;
868 for (Use &U : F->uses()) {
869 CallSite CS(U.getUser());
870 // Must be a direct call.
871 if (CS.getInstruction() == nullptr || !CS.isCallee(&U))
874 // Can't change signature of musttail callee
875 if (CS.isMustTailCall())
878 if (CS.getInstruction()->getParent()->getParent() == F)
879 isSelfRecursive = true;
882 // Can't change signature of musttail caller
883 // FIXME: Support promoting whole chain of musttail functions
884 for (BasicBlock &BB : *F)
885 if (BB.getTerminatingMustTailCall())
888 const DataLayout &DL = F->getParent()->getDataLayout();
890 AAResults &AAR = AARGetter(*F);
892 // Check to see which arguments are promotable. If an argument is promotable,
893 // add it to ArgsToPromote.
894 SmallPtrSet<Argument *, 8> ArgsToPromote;
895 SmallPtrSet<Argument *, 8> ByValArgsToTransform;
896 for (Argument *PtrArg : PointerArgs) {
897 Type *AgTy = cast<PointerType>(PtrArg->getType())->getElementType();
899 // Replace sret attribute with noalias. This reduces register pressure by
900 // avoiding a register copy.
901 if (PtrArg->hasStructRetAttr()) {
902 unsigned ArgNo = PtrArg->getArgNo();
903 F->removeParamAttr(ArgNo, Attribute::StructRet);
904 F->addParamAttr(ArgNo, Attribute::NoAlias);
905 for (Use &U : F->uses()) {
906 CallSite CS(U.getUser());
907 CS.removeParamAttr(ArgNo, Attribute::StructRet);
908 CS.addParamAttr(ArgNo, Attribute::NoAlias);
912 // If this is a byval argument, and if the aggregate type is small, just
913 // pass the elements, which is always safe, if the passed value is densely
914 // packed or if we can prove the padding bytes are never accessed. This does
915 // not apply to inalloca.
916 bool isSafeToPromote =
917 PtrArg->hasByValAttr() &&
918 (isDenselyPacked(AgTy, DL) || !canPaddingBeAccessed(PtrArg));
919 if (isSafeToPromote) {
920 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
921 if (MaxElements > 0 && STy->getNumElements() > MaxElements) {
922 LLVM_DEBUG(dbgs() << "argpromotion disable promoting argument '"
924 << "' because it would require adding more"
925 << " than " << MaxElements
926 << " arguments to the function.\n");
930 // If all the elements are single-value types, we can promote it.
931 bool AllSimple = true;
932 for (const auto *EltTy : STy->elements()) {
933 if (!EltTy->isSingleValueType()) {
939 // Safe to transform, don't even bother trying to "promote" it.
940 // Passing the elements as a scalar will allow sroa to hack on
941 // the new alloca we introduce.
943 ByValArgsToTransform.insert(PtrArg);
949 // If the argument is a recursive type and we're in a recursive
950 // function, we could end up infinitely peeling the function argument.
951 if (isSelfRecursive) {
952 if (StructType *STy = dyn_cast<StructType>(AgTy)) {
953 bool RecursiveType = false;
954 for (const auto *EltTy : STy->elements()) {
955 if (EltTy == PtrArg->getType()) {
956 RecursiveType = true;
965 // Otherwise, see if we can promote the pointer to its value.
966 if (isSafeToPromoteArgument(PtrArg, PtrArg->hasByValOrInAllocaAttr(), AAR,
968 ArgsToPromote.insert(PtrArg);
971 // No promotable pointer arguments.
972 if (ArgsToPromote.empty() && ByValArgsToTransform.empty())
975 if (!areFunctionArgsABICompatible(*F, TTI, ArgsToPromote,
976 ByValArgsToTransform))
979 return doPromotion(F, ArgsToPromote, ByValArgsToTransform, ReplaceCallSite);
982 PreservedAnalyses ArgumentPromotionPass::run(LazyCallGraph::SCC &C,
983 CGSCCAnalysisManager &AM,
985 CGSCCUpdateResult &UR) {
986 bool Changed = false, LocalChange;
988 // Iterate until we stop promoting from this SCC.
992 for (LazyCallGraph::Node &N : C) {
993 Function &OldF = N.getFunction();
995 FunctionAnalysisManager &FAM =
996 AM.getResult<FunctionAnalysisManagerCGSCCProxy>(C, CG).getManager();
997 // FIXME: This lambda must only be used with this function. We should
998 // skip the lambda and just get the AA results directly.
999 auto AARGetter = [&](Function &F) -> AAResults & {
1000 assert(&F == &OldF && "Called with an unexpected function!");
1001 return FAM.getResult<AAManager>(F);
1004 const TargetTransformInfo &TTI = FAM.getResult<TargetIRAnalysis>(OldF);
1006 promoteArguments(&OldF, AARGetter, MaxElements, None, TTI);
1011 // Directly substitute the functions in the call graph. Note that this
1012 // requires the old function to be completely dead and completely
1013 // replaced by the new function. It does no call graph updates, it merely
1014 // swaps out the particular function mapped to a particular node in the
1016 C.getOuterRefSCC().replaceNodeFunction(N, *NewF);
1017 OldF.eraseFromParent();
1020 Changed |= LocalChange;
1021 } while (LocalChange);
1024 return PreservedAnalyses::all();
1026 return PreservedAnalyses::none();
1031 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
1032 struct ArgPromotion : public CallGraphSCCPass {
1033 // Pass identification, replacement for typeid
1036 explicit ArgPromotion(unsigned MaxElements = 3)
1037 : CallGraphSCCPass(ID), MaxElements(MaxElements) {
1038 initializeArgPromotionPass(*PassRegistry::getPassRegistry());
1041 void getAnalysisUsage(AnalysisUsage &AU) const override {
1042 AU.addRequired<AssumptionCacheTracker>();
1043 AU.addRequired<TargetLibraryInfoWrapperPass>();
1044 AU.addRequired<TargetTransformInfoWrapperPass>();
1045 getAAResultsAnalysisUsage(AU);
1046 CallGraphSCCPass::getAnalysisUsage(AU);
1049 bool runOnSCC(CallGraphSCC &SCC) override;
1052 using llvm::Pass::doInitialization;
1054 bool doInitialization(CallGraph &CG) override;
1056 /// The maximum number of elements to expand, or 0 for unlimited.
1057 unsigned MaxElements;
1060 } // end anonymous namespace
1062 char ArgPromotion::ID = 0;
1064 INITIALIZE_PASS_BEGIN(ArgPromotion, "argpromotion",
1065 "Promote 'by reference' arguments to scalars", false,
1067 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
1068 INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
1069 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
1070 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
1071 INITIALIZE_PASS_END(ArgPromotion, "argpromotion",
1072 "Promote 'by reference' arguments to scalars", false, false)
1074 Pass *llvm::createArgumentPromotionPass(unsigned MaxElements) {
1075 return new ArgPromotion(MaxElements);
1078 bool ArgPromotion::runOnSCC(CallGraphSCC &SCC) {
1082 // Get the callgraph information that we need to update to reflect our
1084 CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
1086 LegacyAARGetter AARGetter(*this);
1088 bool Changed = false, LocalChange;
1090 // Iterate until we stop promoting from this SCC.
1092 LocalChange = false;
1093 // Attempt to promote arguments from all functions in this SCC.
1094 for (CallGraphNode *OldNode : SCC) {
1095 Function *OldF = OldNode->getFunction();
1099 auto ReplaceCallSite = [&](CallSite OldCS, CallSite NewCS) {
1100 Function *Caller = OldCS.getInstruction()->getParent()->getParent();
1101 CallGraphNode *NewCalleeNode =
1102 CG.getOrInsertFunction(NewCS.getCalledFunction());
1103 CallGraphNode *CallerNode = CG[Caller];
1104 CallerNode->replaceCallEdge(OldCS, NewCS, NewCalleeNode);
1107 const TargetTransformInfo &TTI =
1108 getAnalysis<TargetTransformInfoWrapperPass>().getTTI(*OldF);
1109 if (Function *NewF = promoteArguments(OldF, AARGetter, MaxElements,
1110 {ReplaceCallSite}, TTI)) {
1113 // Update the call graph for the newly promoted function.
1114 CallGraphNode *NewNode = CG.getOrInsertFunction(NewF);
1115 NewNode->stealCalledFunctionsFrom(OldNode);
1116 if (OldNode->getNumReferences() == 0)
1117 delete CG.removeFunctionFromModule(OldNode);
1119 OldF->setLinkage(Function::ExternalLinkage);
1121 // And updat ethe SCC we're iterating as well.
1122 SCC.ReplaceNode(OldNode, NewNode);
1125 // Remember that we changed something.
1126 Changed |= LocalChange;
1127 } while (LocalChange);
1132 bool ArgPromotion::doInitialization(CallGraph &CG) {
1133 return CallGraphSCCPass::doInitialization(CG);