lib/Transforms/Utils/Mem2Reg.cpp

   1 //===- Mem2Reg.cpp - The -mem2reg pass, a wrapper around the Utils lib ----===//
   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 pass is a simple pass wrapper around the PromoteMemToReg function call
  10 // exposed by the Utils library.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/Transforms/Utils/Mem2Reg.h"
  15 #include "llvm/ADT/Statistic.h"
  16 #include "llvm/Analysis/AssumptionCache.h"
  17 #include "llvm/IR/BasicBlock.h"
  18 #include "llvm/IR/Dominators.h"
  19 #include "llvm/IR/Function.h"
  20 #include "llvm/IR/Instructions.h"
  21 #include "llvm/IR/PassManager.h"
  22 #include "llvm/Pass.h"
  23 #include "llvm/Support/Casting.h"
  24 #include "llvm/Transforms/Utils.h"
  25 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
  26 #include <vector>
  27
  28 using namespace llvm;
  29
  30 #define DEBUG_TYPE "mem2reg"
  31
  32 STATISTIC(NumPromoted, "Number of alloca's promoted");
  33
  34 static bool promoteMemoryToRegister(Function &F, DominatorTree &DT,
  35                                     AssumptionCache &AC) {
  36   std::vector<AllocaInst *> Allocas;
  37   BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
  38   bool Changed = false;
  39
  40   while (true) {
  41     Allocas.clear();
  42
  43     // Find allocas that are safe to promote, by looking at all instructions in
  44     // the entry node
  45     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
  46       if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
  47         if (isAllocaPromotable(AI))
  48           Allocas.push_back(AI);
  49
  50     if (Allocas.empty())
  51       break;
  52
  53     PromoteMemToReg(Allocas, DT, &AC);
  54     NumPromoted += Allocas.size();
  55     Changed = true;
  56   }
  57   return Changed;
  58 }
  59
  60 PreservedAnalyses PromotePass::run(Function &F, FunctionAnalysisManager &AM) {
  61   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
  62   auto &AC = AM.getResult<AssumptionAnalysis>(F);
  63   if (!promoteMemoryToRegister(F, DT, AC))
  64     return PreservedAnalyses::all();
  65
  66   PreservedAnalyses PA;
  67   PA.preserveSet<CFGAnalyses>();
  68   return PA;
  69 }
  70
  71 namespace {
  72
  73 struct PromoteLegacyPass : public FunctionPass {
  74   // Pass identification, replacement for typeid
  75   static char ID;
  76
  77   PromoteLegacyPass() : FunctionPass(ID) {
  78     initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
  79   }
  80
  81   // runOnFunction - To run this pass, first we calculate the alloca
  82   // instructions that are safe for promotion, then we promote each one.
  83   bool runOnFunction(Function &F) override {
  84     if (skipFunction(F))
  85       return false;
  86
  87     DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  88     AssumptionCache &AC =
  89         getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
  90     return promoteMemoryToRegister(F, DT, AC);
  91   }
  92
  93   void getAnalysisUsage(AnalysisUsage &AU) const override {
  94     AU.addRequired<AssumptionCacheTracker>();
  95     AU.addRequired<DominatorTreeWrapperPass>();
  96     AU.setPreservesCFG();
  97   }
  98 };
  99
 100 } // end anonymous namespace
 101
 102 char PromoteLegacyPass::ID = 0;
 103
 104 INITIALIZE_PASS_BEGIN(PromoteLegacyPass, "mem2reg", "Promote Memory to "
 105                                                     "Register",
 106                       false, false)
 107 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 108 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 109 INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register",
 110                     false, false)
 111
 112 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
 113 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
 114   return new PromoteLegacyPass();
 115 }