1 //===- Mem2Reg.cpp - The -mem2reg pass, a wrapper around the Utils lib ----===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This pass is a simple pass wrapper around the PromoteMemToReg function call 11 // exposed by the Utils library. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "llvm/Transforms/Utils/Mem2Reg.h" 16 #include "llvm/ADT/Statistic.h" 17 #include "llvm/Analysis/AssumptionCache.h" 18 #include "llvm/IR/Dominators.h" 19 #include "llvm/IR/Function.h" 20 #include "llvm/IR/Instructions.h" 21 #include "llvm/Transforms/Scalar.h" 22 #include "llvm/Transforms/Utils/PromoteMemToReg.h" 23 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h" 24 using namespace llvm; 25 26 #define DEBUG_TYPE "mem2reg" 27 28 STATISTIC(NumPromoted, "Number of alloca's promoted"); 29 30 static bool promoteMemoryToRegister(Function &F, DominatorTree &DT, 31 AssumptionCache &AC) { 32 std::vector<AllocaInst *> Allocas; 33 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function 34 bool Changed = false; 35 36 while (1) { 37 Allocas.clear(); 38 39 // Find allocas that are safe to promote, by looking at all instructions in 40 // the entry node 41 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I) 42 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca? 43 if (isAllocaPromotable(AI)) 44 Allocas.push_back(AI); 45 46 if (Allocas.empty()) 47 break; 48 49 PromoteMemToReg(Allocas, DT, nullptr, &AC); 50 NumPromoted += Allocas.size(); 51 Changed = true; 52 } 53 return Changed; 54 } 55 56 PreservedAnalyses PromotePass::run(Function &F, AnalysisManager<Function> &AM) { 57 auto &DT = AM.getResult<DominatorTreeAnalysis>(F); 58 auto &AC = AM.getResult<AssumptionAnalysis>(F); 59 if (!promoteMemoryToRegister(F, DT, AC)) 60 return PreservedAnalyses::all(); 61 62 // FIXME: This pass should preserve the CFG. 63 // There's currently no way to do it in the new PM. 64 // In the old PM this pass preserved a fair amount of "orthogonal" 65 // transformation passes. This concept has no sense in the new PM, 66 // therefore we don't preserve them here. 67 return PreservedAnalyses::none(); 68 } 69 70 namespace { 71 struct PromoteLegacyPass : public FunctionPass { 72 static char ID; // Pass identification, replacement for typeid 73 PromoteLegacyPass() : FunctionPass(ID) { 74 initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry()); 75 } 76 77 // runOnFunction - To run this pass, first we calculate the alloca 78 // instructions that are safe for promotion, then we promote each one. 79 // 80 bool runOnFunction(Function &F) override { 81 if (skipFunction(F)) 82 return false; 83 84 DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree(); 85 AssumptionCache &AC = 86 getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F); 87 return promoteMemoryToRegister(F, DT, AC); 88 } 89 90 void getAnalysisUsage(AnalysisUsage &AU) const override { 91 AU.addRequired<AssumptionCacheTracker>(); 92 AU.addRequired<DominatorTreeWrapperPass>(); 93 AU.setPreservesCFG(); 94 } 95 }; 96 } // end of anonymous namespace 97 98 char PromoteLegacyPass::ID = 0; 99 INITIALIZE_PASS_BEGIN(PromoteLegacyPass, "mem2reg", "Promote Memory to " 100 "Register", 101 false, false) 102 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) 103 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass) 104 INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register", 105 false, false) 106 107 // createPromoteMemoryToRegister - Provide an entry point to create this pass. 108 // 109 FunctionPass *llvm::createPromoteMemoryToRegisterPass() { 110 return new PromoteLegacyPass(); 111 } 112