llvm/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/InitializePasses.h"
  23 #include "llvm/Pass.h"
  24 #include "llvm/Support/Casting.h"
  25 #include "llvm/Transforms/Utils.h"
  26 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
  27 #include <vector>
  28
  29 using namespace llvm;
  30
  31 #define DEBUG_TYPE "mem2reg"
  32
  33 STATISTIC(NumPromoted, "Number of alloca's promoted");
  34
  35 static bool promoteMemoryToRegister(Function &F, DominatorTree &DT,
  36                                     AssumptionCache &AC) {
  37   std::vector<AllocaInst *> Allocas;
  38   BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
  39   bool Changed = false;
  40
  41   while (true) {
  42     Allocas.clear();
  43
  44     // Find allocas that are safe to promote, by looking at all instructions in
  45     // the entry node
  46     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
  47       if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
  48         if (isAllocaPromotable(AI))
  49           Allocas.push_back(AI);
  50
  51     if (Allocas.empty())
  52       break;
  53
  54     PromoteMemToReg(Allocas, DT, &AC);
  55     NumPromoted += Allocas.size();
  56     Changed = true;
  57   }
  58   return Changed;
  59 }
  60
  61 PreservedAnalyses PromotePass::run(Function &F, FunctionAnalysisManager &AM) {
  62   auto &DT = AM.getResult<DominatorTreeAnalysis>(F);
  63   auto &AC = AM.getResult<AssumptionAnalysis>(F);
  64   if (!promoteMemoryToRegister(F, DT, AC))
  65     return PreservedAnalyses::all();
  66
  67   PreservedAnalyses PA;
  68   PA.preserveSet<CFGAnalyses>();
  69   return PA;
  70 }
  71
  72 namespace {
  73
  74 struct PromoteLegacyPass : public FunctionPass {
  75   // Pass identification, replacement for typeid
  76   static char ID;
  77   bool ForcePass; /// If true, forces pass to execute, instead of skipping.
  78
  79   PromoteLegacyPass() : FunctionPass(ID), ForcePass(false) {
  80     initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
  81   }
  82   PromoteLegacyPass(bool IsForced) : FunctionPass(ID), ForcePass(IsForced) {
  83     initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
  84   }
  85
  86   // runOnFunction - To run this pass, first we calculate the alloca
  87   // instructions that are safe for promotion, then we promote each one.
  88   bool runOnFunction(Function &F) override {
  89     if (!ForcePass && skipFunction(F))
  90       return false;
  91
  92     DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
  93     AssumptionCache &AC =
  94         getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
  95     return promoteMemoryToRegister(F, DT, AC);
  96   }
  97
  98   void getAnalysisUsage(AnalysisUsage &AU) const override {
  99     AU.addRequired<AssumptionCacheTracker>();
 100     AU.addRequired<DominatorTreeWrapperPass>();
 101     AU.setPreservesCFG();
 102   }
 103 };
 104
 105 } // end anonymous namespace
 106
 107 char PromoteLegacyPass::ID = 0;
 108
 109 INITIALIZE_PASS_BEGIN(PromoteLegacyPass, "mem2reg", "Promote Memory to "
 110                                                     "Register",
 111                       false, false)
 112 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
 113 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
 114 INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register",
 115                     false, false)
 116
 117 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
 118 FunctionPass *llvm::createPromoteMemoryToRegisterPass(bool IsForced) {
 119   return new PromoteLegacyPass(IsForced);
 120 }