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      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 
     78   PromoteLegacyPass() : FunctionPass(ID) {
     79     initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
     80   }
     81 
     82   // runOnFunction - To run this pass, first we calculate the alloca
     83   // instructions that are safe for promotion, then we promote each one.
     84   bool runOnFunction(Function &F) override {
     85     if (skipFunction(F))
     86       return false;
     87 
     88     DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
     89     AssumptionCache &AC =
     90         getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
     91     return promoteMemoryToRegister(F, DT, AC);
     92   }
     93 
     94   void getAnalysisUsage(AnalysisUsage &AU) const override {
     95     AU.addRequired<AssumptionCacheTracker>();
     96     AU.addRequired<DominatorTreeWrapperPass>();
     97     AU.setPreservesCFG();
     98   }
     99 };
    100 
    101 } // end anonymous namespace
    102 
    103 char PromoteLegacyPass::ID = 0;
    104 
    105 INITIALIZE_PASS_BEGIN(PromoteLegacyPass, "mem2reg", "Promote Memory to "
    106                                                     "Register",
    107                       false, false)
    108 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
    109 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
    110 INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register",
    111                     false, false)
    112 
    113 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
    114 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
    115   return new PromoteLegacyPass();
    116 }
    117