| //===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This transformation implements the well known scalar replacement of |
| // aggregates transformation. This xform breaks up alloca instructions of |
| // aggregate type (structure or array) into individual alloca instructions for |
| // each member (if possible). Then, if possible, it transforms the individual |
| // alloca instructions into nice clean scalar SSA form. |
| // |
| // This combines a simple SRoA algorithm with the Mem2Reg algorithm because |
| // often interact, especially for C++ programs. As such, iterating between |
| // SRoA, then Mem2Reg until we run out of things to promote works well. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Constants.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Function.h" |
| #include "llvm/Pass.h" |
| #include "llvm/iMemory.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Transforms/Utils/PromoteMemToReg.h" |
| #include "Support/Debug.h" |
| #include "Support/Statistic.h" |
| #include "Support/StringExtras.h" |
| |
| namespace llvm { |
| |
| namespace { |
| Statistic<> NumReplaced("scalarrepl", "Number of allocas broken up"); |
| Statistic<> NumPromoted("scalarrepl", "Number of allocas promoted"); |
| |
| struct SROA : public FunctionPass { |
| bool runOnFunction(Function &F); |
| |
| bool performScalarRepl(Function &F); |
| bool performPromotion(Function &F); |
| |
| // getAnalysisUsage - This pass does not require any passes, but we know it |
| // will not alter the CFG, so say so. |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<DominatorTree>(); |
| AU.addRequired<DominanceFrontier>(); |
| AU.addRequired<TargetData>(); |
| AU.setPreservesCFG(); |
| } |
| |
| private: |
| bool isSafeElementUse(Value *Ptr); |
| bool isSafeUseOfAllocation(Instruction *User); |
| bool isSafeAllocaToPromote(AllocationInst *AI); |
| AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocationInst *Base); |
| }; |
| |
| RegisterOpt<SROA> X("scalarrepl", "Scalar Replacement of Aggregates"); |
| } |
| |
| // Public interface to the ScalarReplAggregates pass |
| Pass *createScalarReplAggregatesPass() { return new SROA(); } |
| |
| |
| bool SROA::runOnFunction(Function &F) { |
| bool Changed = performPromotion(F); |
| while (1) { |
| bool LocalChange = performScalarRepl(F); |
| if (!LocalChange) break; // No need to repromote if no scalarrepl |
| Changed = true; |
| LocalChange = performPromotion(F); |
| if (!LocalChange) break; // No need to re-scalarrepl if no promotion |
| } |
| |
| return Changed; |
| } |
| |
| |
| bool SROA::performPromotion(Function &F) { |
| std::vector<AllocaInst*> Allocas; |
| const TargetData &TD = getAnalysis<TargetData>(); |
| DominatorTree &DT = getAnalysis<DominatorTree>(); |
| DominanceFrontier &DF = getAnalysis<DominanceFrontier>(); |
| |
| BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function |
| |
| bool Changed = false; |
| |
| while (1) { |
| Allocas.clear(); |
| |
| // Find allocas that are safe to promote, by looking at all instructions in |
| // the entry node |
| for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) |
| if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? |
| if (isAllocaPromotable(AI, TD)) |
| Allocas.push_back(AI); |
| |
| if (Allocas.empty()) break; |
| |
| PromoteMemToReg(Allocas, DT, DF, TD); |
| NumPromoted += Allocas.size(); |
| Changed = true; |
| } |
| |
| return Changed; |
| } |
| |
| |
| // performScalarRepl - This algorithm is a simple worklist driven algorithm, |
| // which runs on all of the malloc/alloca instructions in the function, removing |
| // them if they are only used by getelementptr instructions. |
| // |
| bool SROA::performScalarRepl(Function &F) { |
| std::vector<AllocationInst*> WorkList; |
| |
| // Scan the entry basic block, adding any alloca's and mallocs to the worklist |
| BasicBlock &BB = F.getEntryBlock(); |
| for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I) |
| if (AllocationInst *A = dyn_cast<AllocationInst>(I)) |
| WorkList.push_back(A); |
| |
| // Process the worklist |
| bool Changed = false; |
| while (!WorkList.empty()) { |
| AllocationInst *AI = WorkList.back(); |
| WorkList.pop_back(); |
| |
| // We cannot transform the allocation instruction if it is an array |
| // allocation (allocations OF arrays are ok though), and an allocation of a |
| // scalar value cannot be decomposed at all. |
| // |
| if (AI->isArrayAllocation() || |
| (!isa<StructType>(AI->getAllocatedType()) && |
| !isa<ArrayType>(AI->getAllocatedType()))) continue; |
| |
| // Check that all of the users of the allocation are capable of being |
| // transformed. |
| if (!isSafeAllocaToPromote(AI)) |
| continue; |
| |
| DEBUG(std::cerr << "Found inst to xform: " << *AI); |
| Changed = true; |
| |
| std::vector<AllocaInst*> ElementAllocas; |
| if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) { |
| ElementAllocas.reserve(ST->getNumContainedTypes()); |
| for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) { |
| AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0, |
| AI->getName() + "." + utostr(i), AI); |
| ElementAllocas.push_back(NA); |
| WorkList.push_back(NA); // Add to worklist for recursive processing |
| } |
| } else { |
| const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType()); |
| ElementAllocas.reserve(AT->getNumElements()); |
| const Type *ElTy = AT->getElementType(); |
| for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) { |
| AllocaInst *NA = new AllocaInst(ElTy, 0, |
| AI->getName() + "." + utostr(i), AI); |
| ElementAllocas.push_back(NA); |
| WorkList.push_back(NA); // Add to worklist for recursive processing |
| } |
| } |
| |
| // Now that we have created the alloca instructions that we want to use, |
| // expand the getelementptr instructions to use them. |
| // |
| for (Value::use_iterator I = AI->use_begin(), E = AI->use_end(); |
| I != E; ++I) { |
| Instruction *User = cast<Instruction>(*I); |
| if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { |
| // We now know that the GEP is of the form: GEP <ptr>, 0, <cst> |
| uint64_t Idx = cast<ConstantInt>(GEPI->getOperand(2))->getRawValue(); |
| |
| assert(Idx < ElementAllocas.size() && "Index out of range?"); |
| AllocaInst *AllocaToUse = ElementAllocas[Idx]; |
| |
| Value *RepValue; |
| if (GEPI->getNumOperands() == 3) { |
| // Do not insert a new getelementptr instruction with zero indices, |
| // only to have it optimized out later. |
| RepValue = AllocaToUse; |
| } else { |
| // We are indexing deeply into the structure, so we still need a |
| // getelement ptr instruction to finish the indexing. This may be |
| // expanded itself once the worklist is rerun. |
| // |
| std::string OldName = GEPI->getName(); // Steal the old name... |
| std::vector<Value*> NewArgs; |
| NewArgs.push_back(Constant::getNullValue(Type::LongTy)); |
| NewArgs.insert(NewArgs.end(), GEPI->op_begin()+3, GEPI->op_end()); |
| GEPI->setName(""); |
| RepValue = |
| new GetElementPtrInst(AllocaToUse, NewArgs, OldName, GEPI); |
| } |
| |
| // Move all of the users over to the new GEP. |
| GEPI->replaceAllUsesWith(RepValue); |
| // Delete the old GEP |
| GEPI->getParent()->getInstList().erase(GEPI); |
| } else { |
| assert(0 && "Unexpected instruction type!"); |
| } |
| } |
| |
| // Finally, delete the Alloca instruction |
| AI->getParent()->getInstList().erase(AI); |
| NumReplaced++; |
| } |
| |
| return Changed; |
| } |
| |
| |
| /// isSafeUseOfAllocation - Check to see if this user is an allowed use for an |
| /// aggregate allocation. |
| /// |
| bool SROA::isSafeUseOfAllocation(Instruction *User) { |
| if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) { |
| // The GEP is safe to transform if it is of the form GEP <ptr>, 0, <cst> |
| if (GEPI->getNumOperands() <= 2 || |
| GEPI->getOperand(1) != Constant::getNullValue(Type::LongTy) || |
| !isa<Constant>(GEPI->getOperand(2)) || |
| isa<ConstantExpr>(GEPI->getOperand(2))) |
| return false; |
| |
| // If this is a use of an array allocation, do a bit more checking for |
| // sanity. |
| if (GEPI->getOperand(2)->getType() == Type::LongTy) { |
| const PointerType *PTy =cast<PointerType>(GEPI->getOperand(0)->getType()); |
| const ArrayType *AT = cast<ArrayType>(PTy->getElementType()); |
| int64_t NumElements = AT->getNumElements(); |
| |
| // Check to make sure that index falls within the array. If not, |
| // something funny is going on, so we won't do the optimization. |
| // |
| if (cast<ConstantSInt>(GEPI->getOperand(2))->getValue() >= NumElements || |
| cast<ConstantSInt>(GEPI->getOperand(2))->getValue() < 0) |
| return false; |
| } |
| |
| // If there are any non-simple uses of this getelementptr, make sure to |
| // reject them. |
| if (isSafeElementUse(GEPI)) |
| return true; |
| } |
| return false; |
| } |
| |
| /// isSafeElementUse - Check to see if this use is an allowed use for a |
| /// getelementptr instruction of an array aggregate allocation. |
| /// |
| bool SROA::isSafeElementUse(Value *Ptr) { |
| for (Value::use_iterator I = Ptr->use_begin(), E = Ptr->use_end(); |
| I != E; ++I) { |
| Instruction *User = cast<Instruction>(*I); |
| switch (User->getOpcode()) { |
| case Instruction::Load: break; |
| case Instruction::Store: |
| // Store is ok if storing INTO the pointer, not storing the pointer |
| if (User->getOperand(0) == Ptr) return false; |
| break; |
| case Instruction::GetElementPtr: { |
| GetElementPtrInst *GEP = cast<GetElementPtrInst>(User); |
| if (GEP->getNumOperands() > 1) { |
| if (!isa<Constant>(GEP->getOperand(1)) || |
| !cast<Constant>(GEP->getOperand(1))->isNullValue()) |
| return false; // Using pointer arithmetic to navigate the array... |
| } |
| if (!isSafeElementUse(GEP)) return false; |
| break; |
| } |
| default: |
| DEBUG(std::cerr << " Transformation preventing inst: " << *User); |
| return false; |
| } |
| } |
| return true; // All users look ok :) |
| } |
| |
| |
| /// isSafeStructAllocaToPromote - Check to see if the specified allocation of a |
| /// structure can be broken down into elements. |
| /// |
| bool SROA::isSafeAllocaToPromote(AllocationInst *AI) { |
| // Loop over the use list of the alloca. We can only transform it if all of |
| // the users are safe to transform. |
| // |
| for (Value::use_iterator I = AI->use_begin(), E = AI->use_end(); |
| I != E; ++I) |
| if (!isSafeUseOfAllocation(cast<Instruction>(*I))) { |
| DEBUG(std::cerr << "Cannot transform: " << *AI << " due to user: " |
| << *I); |
| return false; |
| } |
| return true; |
| } |
| |
| } // End llvm namespace |