LLVM API Documentation

Mem2Reg.cpp

Go to the documentation of this file.
00001 //===- Mem2Reg.cpp - The -mem2reg pass, a wrapper around the Utils lib ----===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This pass is a simple pass wrapper around the PromoteMemToReg function call
00011 // exposed by the Utils library.
00012 //
00013 //===----------------------------------------------------------------------===//
00014 
00015 #include "llvm/Transforms/Scalar.h"
00016 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
00017 #include "llvm/Analysis/Dominators.h"
00018 #include "llvm/Instructions.h"
00019 #include "llvm/Function.h"
00020 #include "llvm/Target/TargetData.h"
00021 #include "llvm/ADT/Statistic.h"
00022 using namespace llvm;
00023 
00024 namespace {
00025   Statistic<> NumPromoted("mem2reg", "Number of alloca's promoted");
00026 
00027   struct PromotePass : public FunctionPass {
00028     // runOnFunction - To run this pass, first we calculate the alloca
00029     // instructions that are safe for promotion, then we promote each one.
00030     //
00031     virtual bool runOnFunction(Function &F);
00032 
00033     // getAnalysisUsage - We need dominance frontiers
00034     //
00035     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00036       AU.addRequired<DominatorTree>();
00037       AU.addRequired<DominanceFrontier>();
00038       AU.addRequired<TargetData>();
00039       AU.setPreservesCFG();
00040     }
00041   };
00042 
00043   RegisterOpt<PromotePass> X("mem2reg", "Promote Memory to Register");
00044 }  // end of anonymous namespace
00045 
00046 bool PromotePass::runOnFunction(Function &F) {
00047   std::vector<AllocaInst*> Allocas;
00048   const TargetData &TD = getAnalysis<TargetData>();
00049 
00050   BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function
00051 
00052   bool Changed  = false;
00053 
00054   DominatorTree     &DT = getAnalysis<DominatorTree>();
00055   DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
00056 
00057   while (1) {
00058     Allocas.clear();
00059 
00060     // Find allocas that are safe to promote, by looking at all instructions in
00061     // the entry node
00062     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
00063       if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
00064         if (isAllocaPromotable(AI, TD))
00065           Allocas.push_back(AI);
00066 
00067     if (Allocas.empty()) break;
00068 
00069     PromoteMemToReg(Allocas, DT, DF, TD);
00070     NumPromoted += Allocas.size();
00071     Changed = true;
00072   }
00073 
00074   return Changed;
00075 }
00076 
00077 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
00078 //
00079 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
00080   return new PromotePass();
00081 }