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      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 should also 'preserve the CFG'.
     63   return PreservedAnalyses::none();
     64 }
     65 
     66 namespace {
     67 struct PromoteLegacyPass : public FunctionPass {
     68   static char ID; // Pass identification, replacement for typeid
     69   PromoteLegacyPass() : FunctionPass(ID) {
     70     initializePromoteLegacyPassPass(*PassRegistry::getPassRegistry());
     71   }
     72 
     73   // runOnFunction - To run this pass, first we calculate the alloca
     74   // instructions that are safe for promotion, then we promote each one.
     75   //
     76   bool runOnFunction(Function &F) override {
     77     if (skipFunction(F))
     78       return false;
     79 
     80     DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
     81     AssumptionCache &AC =
     82         getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
     83     return promoteMemoryToRegister(F, DT, AC);
     84   }
     85 
     86   void getAnalysisUsage(AnalysisUsage &AU) const override {
     87     AU.addRequired<AssumptionCacheTracker>();
     88     AU.addRequired<DominatorTreeWrapperPass>();
     89     AU.setPreservesCFG();
     90   }
     91   };
     92 }  // end of anonymous namespace
     93 
     94 char PromoteLegacyPass::ID = 0;
     95 INITIALIZE_PASS_BEGIN(PromoteLegacyPass, "mem2reg", "Promote Memory to "
     96                                                     "Register",
     97                       false, false)
     98 INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
     99 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
    100 INITIALIZE_PASS_END(PromoteLegacyPass, "mem2reg", "Promote Memory to Register",
    101                     false, false)
    102 
    103 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
    104 //
    105 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
    106   return new PromoteLegacyPass();
    107 }
    108