LLVM API Documentation

Mem2Reg.cpp

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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/Transforms/Utils/UnifyFunctionExitNodes.h"
00018 #include "llvm/Analysis/Dominators.h"
00019 #include "llvm/Instructions.h"
00020 #include "llvm/Function.h"
00021 #include "llvm/Target/TargetData.h"
00022 #include "llvm/ADT/Statistic.h"
00023 #include "llvm/Support/Visibility.h"
00024 using namespace llvm;
00025 
00026 namespace {
00027   Statistic<> NumPromoted("mem2reg", "Number of alloca's promoted");
00028 
00029   struct VISIBILITY_HIDDEN PromotePass : public FunctionPass {
00030     // runOnFunction - To run this pass, first we calculate the alloca
00031     // instructions that are safe for promotion, then we promote each one.
00032     //
00033     virtual bool runOnFunction(Function &F);
00034 
00035     // getAnalysisUsage - We need dominance frontiers
00036     //
00037     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
00038       AU.addRequired<DominatorTree>();
00039       AU.addRequired<DominanceFrontier>();
00040       AU.addRequired<TargetData>();
00041       AU.setPreservesCFG();
00042       // This is a cluster of orthogonal Transforms 
00043       AU.addPreserved<UnifyFunctionExitNodes>();
00044       AU.addPreservedID(LowerSelectID);
00045       AU.addPreservedID(LowerSwitchID);
00046       AU.addPreservedID(LowerInvokePassID);
00047       AU.addPreservedID(LowerAllocationsID);
00048     }
00049   };
00050 
00051   RegisterOpt<PromotePass> X("mem2reg", "Promote Memory to Register");
00052 }  // end of anonymous namespace
00053 
00054 bool PromotePass::runOnFunction(Function &F) {
00055   std::vector<AllocaInst*> Allocas;
00056   const TargetData &TD = getAnalysis<TargetData>();
00057 
00058   BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function
00059 
00060   bool Changed  = false;
00061 
00062   DominatorTree     &DT = getAnalysis<DominatorTree>();
00063   DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
00064 
00065   while (1) {
00066     Allocas.clear();
00067 
00068     // Find allocas that are safe to promote, by looking at all instructions in
00069     // the entry node
00070     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
00071       if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
00072         if (isAllocaPromotable(AI, TD))
00073           Allocas.push_back(AI);
00074 
00075     if (Allocas.empty()) break;
00076 
00077     PromoteMemToReg(Allocas, DT, DF, TD);
00078     NumPromoted += Allocas.size();
00079     Changed = true;
00080   }
00081 
00082   return Changed;
00083 }
00084 
00085 // Publically exposed interface to pass...
00086 const PassInfo *llvm::PromoteMemoryToRegisterID = X.getPassInfo();
00087 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
00088 //
00089 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
00090   return new PromotePass();
00091 }