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 #include "llvm/Support/Compiler.h"
  24 using namespace llvm;
  25
  26 STATISTIC(NumPromoted, "Number of alloca's promoted");
  27
  28 namespace {
  29   struct VISIBILITY_HIDDEN PromotePass : public FunctionPass {
  30     static char ID; // Pass identification, replacement for typeid
  31     PromotePass() : FunctionPass(&ID) {}
  32
  33     // runOnFunction - To run this pass, first we calculate the alloca
  34     // instructions that are safe for promotion, then we promote each one.
  35     //
  36     virtual bool runOnFunction(Function &F);
  37
  38     // getAnalysisUsage - We need dominance frontiers
  39     //
  40     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  41       AU.addRequired<DominatorTree>();
  42       AU.addRequired<DominanceFrontier>();
  43       AU.setPreservesCFG();
  44       // This is a cluster of orthogonal Transforms
  45       AU.addPreserved<UnifyFunctionExitNodes>();
  46       AU.addPreservedID(LowerSwitchID);
  47       AU.addPreservedID(LowerInvokePassID);
  48       AU.addPreservedID(LowerAllocationsID);
  49     }
  50   };
  51 }  // end of anonymous namespace
  52
  53 char PromotePass::ID = 0;
  54 static RegisterPass<PromotePass> X("mem2reg", "Promote Memory to Register");
  55
  56 bool PromotePass::runOnFunction(Function &F) {
  57   std::vector<AllocaInst*> Allocas;
  58
  59   BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function
  60
  61   bool Changed  = false;
  62
  63   DominatorTree &DT = getAnalysis<DominatorTree>();
  64   DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
  65
  66   while (1) {
  67     Allocas.clear();
  68
  69     // Find allocas that are safe to promote, by looking at all instructions in
  70     // the entry node
  71     for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
  72       if (AllocaInst *AI = dyn_cast<AllocaInst>(I))       // Is it an alloca?
  73         if (isAllocaPromotable(AI))
  74           Allocas.push_back(AI);
  75
  76     if (Allocas.empty()) break;
  77
  78     PromoteMemToReg(Allocas, DT, DF, F.getContext());
  79     NumPromoted += Allocas.size();
  80     Changed = true;
  81   }
  82
  83   return Changed;
  84 }
  85
  86 // Publically exposed interface to pass...
  87 const PassInfo *const llvm::PromoteMemoryToRegisterID = &X;
  88 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
  89 //
  90 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
  91   return new PromotePass();
  92 }