1 //===- Reg2Mem.cpp - Convert registers to allocas -------------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file demotes all registers to memory references. It is intended to be 10 // the inverse of PromoteMemoryToRegister. By converting to loads, the only 11 // values live across basic blocks are allocas and loads before phi nodes. 12 // It is intended that this should make CFG hacking much easier. 13 // To make later hacking easier, the entry block is split into two, such that 14 // all introduced allocas and nothing else are in the entry block. 15 // 16 //===----------------------------------------------------------------------===// 17 18 #include "llvm/Transforms/Scalar/Reg2Mem.h" 19 #include "llvm/ADT/Statistic.h" 20 #include "llvm/Analysis/LoopInfo.h" 21 #include "llvm/IR/BasicBlock.h" 22 #include "llvm/IR/CFG.h" 23 #include "llvm/IR/Dominators.h" 24 #include "llvm/IR/Function.h" 25 #include "llvm/IR/InstIterator.h" 26 #include "llvm/IR/Instructions.h" 27 #include "llvm/IR/PassManager.h" 28 #include "llvm/InitializePasses.h" 29 #include "llvm/Pass.h" 30 #include "llvm/Transforms/Scalar.h" 31 #include "llvm/Transforms/Utils.h" 32 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 33 #include "llvm/Transforms/Utils/Local.h" 34 #include <list> 35 using namespace llvm; 36 37 #define DEBUG_TYPE "reg2mem" 38 39 STATISTIC(NumRegsDemoted, "Number of registers demoted"); 40 STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted"); 41 42 static bool valueEscapes(const Instruction &Inst) { 43 if (!Inst.getType()->isSized()) 44 return false; 45 46 const BasicBlock *BB = Inst.getParent(); 47 for (const User *U : Inst.users()) { 48 const Instruction *UI = cast<Instruction>(U); 49 if (UI->getParent() != BB || isa<PHINode>(UI)) 50 return true; 51 } 52 return false; 53 } 54 55 static bool runPass(Function &F) { 56 // Insert all new allocas into entry block. 57 BasicBlock *BBEntry = &F.getEntryBlock(); 58 assert(pred_empty(BBEntry) && 59 "Entry block to function must not have predecessors!"); 60 61 // Find first non-alloca instruction and create insertion point. This is 62 // safe if block is well-formed: it always have terminator, otherwise 63 // we'll get and assertion. 64 BasicBlock::iterator I = BBEntry->begin(); 65 while (isa<AllocaInst>(I)) ++I; 66 67 CastInst *AllocaInsertionPoint = new BitCastInst( 68 Constant::getNullValue(Type::getInt32Ty(F.getContext())), 69 Type::getInt32Ty(F.getContext()), "reg2mem alloca point", &*I); 70 71 // Find the escaped instructions. But don't create stack slots for 72 // allocas in entry block. 73 std::list<Instruction*> WorkList; 74 for (Instruction &I : instructions(F)) 75 if (!(isa<AllocaInst>(I) && I.getParent() == BBEntry) && valueEscapes(I)) 76 WorkList.push_front(&I); 77 78 // Demote escaped instructions 79 NumRegsDemoted += WorkList.size(); 80 for (Instruction *I : WorkList) 81 DemoteRegToStack(*I, false, AllocaInsertionPoint); 82 83 WorkList.clear(); 84 85 // Find all phi's 86 for (BasicBlock &BB : F) 87 for (auto &Phi : BB.phis()) 88 WorkList.push_front(&Phi); 89 90 // Demote phi nodes 91 NumPhisDemoted += WorkList.size(); 92 for (Instruction *I : WorkList) 93 DemotePHIToStack(cast<PHINode>(I), AllocaInsertionPoint); 94 95 return true; 96 } 97 98 PreservedAnalyses RegToMemPass::run(Function &F, FunctionAnalysisManager &AM) { 99 auto *DT = &AM.getResult<DominatorTreeAnalysis>(F); 100 auto *LI = &AM.getResult<LoopAnalysis>(F); 101 unsigned N = SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions(DT, LI)); 102 bool Changed = runPass(F); 103 if (N == 0 && !Changed) 104 return PreservedAnalyses::all(); 105 PreservedAnalyses PA; 106 PA.preserve<DominatorTreeAnalysis>(); 107 PA.preserve<LoopAnalysis>(); 108 return PA; 109 } 110 111 namespace { 112 struct RegToMemLegacy : public FunctionPass { 113 static char ID; // Pass identification, replacement for typeid 114 RegToMemLegacy() : FunctionPass(ID) { 115 initializeRegToMemLegacyPass(*PassRegistry::getPassRegistry()); 116 } 117 118 void getAnalysisUsage(AnalysisUsage &AU) const override { 119 AU.addRequiredID(BreakCriticalEdgesID); 120 AU.addPreservedID(BreakCriticalEdgesID); 121 } 122 123 bool runOnFunction(Function &F) override { 124 if (F.isDeclaration() || skipFunction(F)) 125 return false; 126 return runPass(F); 127 } 128 }; 129 } // namespace 130 131 char RegToMemLegacy::ID = 0; 132 INITIALIZE_PASS_BEGIN(RegToMemLegacy, "reg2mem", 133 "Demote all values to stack slots", false, false) 134 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges) 135 INITIALIZE_PASS_END(RegToMemLegacy, "reg2mem", 136 "Demote all values to stack slots", false, false) 137 138 // createDemoteRegisterToMemory - Provide an entry point to create this pass. 139 char &llvm::DemoteRegisterToMemoryID = RegToMemLegacy::ID; 140 FunctionPass *llvm::createDemoteRegisterToMemoryPass() { 141 return new RegToMemLegacy(); 142 } 143