| //===- Reg2Mem.cpp - Convert registers to allocas -------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file demotes all registers to memory references. It is intended to be |
| // the inverse of PromoteMemoryToRegister. By converting to loads, the only |
| // values live across basic blocks are allocas and loads before phi nodes. |
| // It is intended that this should make CFG hacking much easier. |
| // To make later hacking easier, the entry block is split into two, such that |
| // all introduced allocas and nothing else are in the entry block. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar/Reg2Mem.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/IR/BasicBlock.h" |
| #include "llvm/IR/CFG.h" |
| #include "llvm/IR/Dominators.h" |
| #include "llvm/IR/Function.h" |
| #include "llvm/IR/InstIterator.h" |
| #include "llvm/IR/Instructions.h" |
| #include "llvm/IR/PassManager.h" |
| #include "llvm/InitializePasses.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Transforms/Utils.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include <list> |
| using namespace llvm; |
| |
| #define DEBUG_TYPE "reg2mem" |
| |
| STATISTIC(NumRegsDemoted, "Number of registers demoted"); |
| STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted"); |
| |
| static bool valueEscapes(const Instruction &Inst) { |
| if (!Inst.getType()->isSized()) |
| return false; |
| |
| const BasicBlock *BB = Inst.getParent(); |
| for (const User *U : Inst.users()) { |
| const Instruction *UI = cast<Instruction>(U); |
| if (UI->getParent() != BB || isa<PHINode>(UI)) |
| return true; |
| } |
| return false; |
| } |
| |
| static bool runPass(Function &F) { |
| // Insert all new allocas into entry block. |
| BasicBlock *BBEntry = &F.getEntryBlock(); |
| assert(pred_empty(BBEntry) && |
| "Entry block to function must not have predecessors!"); |
| |
| // Find first non-alloca instruction and create insertion point. This is |
| // safe if block is well-formed: it always have terminator, otherwise |
| // we'll get and assertion. |
| BasicBlock::iterator I = BBEntry->begin(); |
| while (isa<AllocaInst>(I)) ++I; |
| |
| CastInst *AllocaInsertionPoint = new BitCastInst( |
| Constant::getNullValue(Type::getInt32Ty(F.getContext())), |
| Type::getInt32Ty(F.getContext()), "reg2mem alloca point", &*I); |
| |
| // Find the escaped instructions. But don't create stack slots for |
| // allocas in entry block. |
| std::list<Instruction*> WorkList; |
| for (Instruction &I : instructions(F)) |
| if (!(isa<AllocaInst>(I) && I.getParent() == BBEntry) && valueEscapes(I)) |
| WorkList.push_front(&I); |
| |
| // Demote escaped instructions |
| NumRegsDemoted += WorkList.size(); |
| for (Instruction *I : WorkList) |
| DemoteRegToStack(*I, false, AllocaInsertionPoint); |
| |
| WorkList.clear(); |
| |
| // Find all phi's |
| for (BasicBlock &BB : F) |
| for (auto &Phi : BB.phis()) |
| WorkList.push_front(&Phi); |
| |
| // Demote phi nodes |
| NumPhisDemoted += WorkList.size(); |
| for (Instruction *I : WorkList) |
| DemotePHIToStack(cast<PHINode>(I), AllocaInsertionPoint); |
| |
| return true; |
| } |
| |
| PreservedAnalyses RegToMemPass::run(Function &F, FunctionAnalysisManager &AM) { |
| auto *DT = &AM.getResult<DominatorTreeAnalysis>(F); |
| auto *LI = &AM.getResult<LoopAnalysis>(F); |
| unsigned N = SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions(DT, LI)); |
| bool Changed = runPass(F); |
| if (N == 0 && !Changed) |
| return PreservedAnalyses::all(); |
| PreservedAnalyses PA; |
| PA.preserve<DominatorTreeAnalysis>(); |
| PA.preserve<LoopAnalysis>(); |
| return PA; |
| } |
| |
| namespace { |
| struct RegToMemLegacy : public FunctionPass { |
| static char ID; // Pass identification, replacement for typeid |
| RegToMemLegacy() : FunctionPass(ID) { |
| initializeRegToMemLegacyPass(*PassRegistry::getPassRegistry()); |
| } |
| |
| void getAnalysisUsage(AnalysisUsage &AU) const override { |
| AU.addRequiredID(BreakCriticalEdgesID); |
| AU.addPreservedID(BreakCriticalEdgesID); |
| } |
| |
| bool runOnFunction(Function &F) override { |
| if (F.isDeclaration() || skipFunction(F)) |
| return false; |
| return runPass(F); |
| } |
| }; |
| } // namespace |
| |
| char RegToMemLegacy::ID = 0; |
| INITIALIZE_PASS_BEGIN(RegToMemLegacy, "reg2mem", |
| "Demote all values to stack slots", false, false) |
| INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges) |
| INITIALIZE_PASS_END(RegToMemLegacy, "reg2mem", |
| "Demote all values to stack slots", false, false) |
| |
| // createDemoteRegisterToMemory - Provide an entry point to create this pass. |
| char &llvm::DemoteRegisterToMemoryID = RegToMemLegacy::ID; |
| FunctionPass *llvm::createDemoteRegisterToMemoryPass() { |
| return new RegToMemLegacy(); |
| } |