lib/Transforms/Utils/Mem2Reg.cpp

   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 #define DEBUG_TYPE "mem2reg"
  16 #include "llvm/Transforms/Scalar.h"
  17 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
  18 #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h"
  19 #include "llvm/Analysis/Dominators.h"
  20 #include "llvm/Instructions.h"
  21 #include "llvm/Function.h"
  22 #include "llvm/ADT/Statistic.h"
  23 using namespace llvm;
  24
  25 STATISTIC(NumPromoted, "Number of alloca's promoted");
  26
  27 namespace {
  28   struct PromotePass : public FunctionPass {
  29     static char ID; // Pass identification, replacement for typeid
  30     PromotePass() : FunctionPass(&ID) {}
  31
  32     // runOnFunction - To run this pass, first we calculate the alloca
  33     // instructions that are safe for promotion, then we promote each one.
  34     //
  35     virtual bool runOnFunction(Function &F);
  36
  37     // getAnalysisUsage - We need dominance frontiers
  38     //
  39     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  40       AU.addRequired<DominatorTree>();
  41       AU.addRequired<DominanceFrontier>();
  42       AU.setPreservesCFG();
  43       // This is a cluster of orthogonal Transforms
  44       AU.addPreserved<UnifyFunctionExitNodes>();
  45       AU.addPreservedID(LowerSwitchID);
  46       AU.addPreservedID(LowerInvokePassID);
  47     }
  48   };
  49 }  // end of anonymous namespace
  50
  51 char PromotePass::ID = 0;
  52 static RegisterPass<PromotePass> X("mem2reg", "Promote Memory to Register");
  53
  54 bool PromotePass::runOnFunction(Function &F) {
  55   std::vector<AllocaInst*> Allocas;
  56
  57   BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function
  58
  59   bool Changed  = false;
  60
  61   DominatorTree &DT = getAnalysis<DominatorTree>();
  62   DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
  63
  64   while (1) {
  65     Allocas.clear();
  66
  67     // Find allocas that are safe to promote, by looking at all instructions in
  68     // the entry node
  69     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
  70       if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
  71         if (isAllocaPromotable(AI))
  72           Allocas.push_back(AI);
  73
  74     if (Allocas.empty()) break;
  75
  76     PromoteMemToReg(Allocas, DT, DF);
  77     NumPromoted += Allocas.size();
  78     Changed = true;
  79   }
  80
  81   return Changed;
  82 }
  83
  84 // Publically exposed interface to pass...
  85 const PassInfo *const llvm::PromoteMemoryToRegisterID = &X;
  86 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
  87 //
  88 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
  89   return new PromotePass();
  90 }