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/Transforms/Scalar.h" 30 #include "llvm/Transforms/Utils.h" 31 #include "llvm/Transforms/Utils/BasicBlockUtils.h" 32 #include "llvm/Transforms/Utils/Local.h" 33 #include <list> 34 using namespace llvm; 35 36 #define DEBUG_TYPE "reg2mem" 37 38 STATISTIC(NumRegsDemoted, "Number of registers demoted"); 39 STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted"); 40 41 static bool valueEscapes(const Instruction &Inst) { 42 if (!Inst.getType()->isSized()) 43 return false; 44 45 const BasicBlock *BB = Inst.getParent(); 46 for (const User *U : Inst.users()) { 47 const Instruction *UI = cast<Instruction>(U); 48 if (UI->getParent() != BB || isa<PHINode>(UI)) 49 return true; 50 } 51 return false; 52 } 53 54 static bool runPass(Function &F) { 55 // Insert all new allocas into entry block. 56 BasicBlock *BBEntry = &F.getEntryBlock(); 57 assert(pred_empty(BBEntry) && 58 "Entry block to function must not have predecessors!"); 59 60 // Find first non-alloca instruction and create insertion point. This is 61 // safe if block is well-formed: it always have terminator, otherwise 62 // we'll get and assertion. 63 BasicBlock::iterator I = BBEntry->begin(); 64 while (isa<AllocaInst>(I)) ++I; 65 66 CastInst *AllocaInsertionPoint = new BitCastInst( 67 Constant::getNullValue(Type::getInt32Ty(F.getContext())), 68 Type::getInt32Ty(F.getContext()), "reg2mem alloca point", I); 69 70 // Find the escaped instructions. But don't create stack slots for 71 // allocas in entry block. 72 std::list<Instruction*> WorkList; 73 for (Instruction &I : instructions(F)) 74 if (!(isa<AllocaInst>(I) && I.getParent() == BBEntry) && valueEscapes(I)) 75 WorkList.push_front(&I); 76 77 // Demote escaped instructions 78 NumRegsDemoted += WorkList.size(); 79 for (Instruction *I : WorkList) 80 DemoteRegToStack(*I, false, AllocaInsertionPoint->getIterator()); 81 82 WorkList.clear(); 83 84 // Find all phi's 85 for (BasicBlock &BB : F) 86 for (auto &Phi : BB.phis()) 87 WorkList.push_front(&Phi); 88 89 // Demote phi nodes 90 NumPhisDemoted += WorkList.size(); 91 for (Instruction *I : WorkList) 92 DemotePHIToStack(cast<PHINode>(I), AllocaInsertionPoint->getIterator()); 93 94 return true; 95 } 96 97 PreservedAnalyses RegToMemPass::run(Function &F, FunctionAnalysisManager &AM) { 98 auto *DT = &AM.getResult<DominatorTreeAnalysis>(F); 99 auto *LI = &AM.getResult<LoopAnalysis>(F); 100 unsigned N = SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions(DT, LI)); 101 bool Changed = runPass(F); 102 if (N == 0 && !Changed) 103 return PreservedAnalyses::all(); 104 PreservedAnalyses PA; 105 PA.preserve<DominatorTreeAnalysis>(); 106 PA.preserve<LoopAnalysis>(); 107 return PA; 108 } 109 110 namespace llvm { 111 112 void initializeRegToMemWrapperPassPass(PassRegistry &); 113 114 class RegToMemWrapperPass : public FunctionPass { 115 public: 116 static char ID; 117 118 RegToMemWrapperPass() : FunctionPass(ID) {} 119 120 void getAnalysisUsage(AnalysisUsage &AU) const override { 121 AU.setPreservesAll(); 122 123 AU.addPreserved<DominatorTreeWrapperPass>(); 124 AU.addRequired<DominatorTreeWrapperPass>(); 125 126 AU.addPreserved<LoopInfoWrapperPass>(); 127 AU.addRequired<LoopInfoWrapperPass>(); 128 } 129 130 bool runOnFunction(Function &F) override { 131 DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 132 LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo(); 133 134 unsigned N = SplitAllCriticalEdges(F, CriticalEdgeSplittingOptions(DT, LI)); 135 bool Changed = runPass(F); 136 return N != 0 || Changed; 137 } 138 }; 139 } // namespace llvm 140 141 INITIALIZE_PASS_BEGIN(RegToMemWrapperPass, "reg2mem", "", true, true) 142 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass); 143 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass); 144 INITIALIZE_PASS_END(RegToMemWrapperPass, "reg2mem", "", true, true) 145 146 char RegToMemWrapperPass::ID = 0; 147 148 FunctionPass *llvm::createRegToMemWrapperPass() { 149 return new RegToMemWrapperPass(); 150 } 151