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       initializePromotePassPass(*PassRegistry::getPassRegistry());
  32     }
  33
  34     // runOnFunction - To run this pass, first we calculate the alloca
  35     // instructions that are safe for promotion, then we promote each one.
  36     //
  37     virtual bool runOnFunction(Function &F);
  38
  39     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  40       AU.addRequired<DominatorTree>();
  41       AU.setPreservesCFG();
  42       // This is a cluster of orthogonal Transforms
  43       AU.addPreserved<UnifyFunctionExitNodes>();
  44       AU.addPreservedID(LowerSwitchID);
  45       AU.addPreservedID(LowerInvokePassID);
  46     }
  47   };
  48 }  // end of anonymous namespace
  49
  50 char PromotePass::ID = 0;
  51 INITIALIZE_PASS_BEGIN(PromotePass, "mem2reg", "Promote Memory to Register",
  52                 false, false)
  53 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
  54 INITIALIZE_PASS_END(PromotePass, "mem2reg", "Promote Memory to Register",
  55                 false, false)
  56
  57 bool PromotePass::runOnFunction(Function &F) {
  58   std::vector<AllocaInst*> Allocas;
  59
  60   BasicBlock &BB = F.getEntryBlock();  // Get the entry node for the function
  61
  62   bool Changed  = false;
  63
  64   DominatorTree &DT = getAnalysis<DominatorTree>();
  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);
  79     NumPromoted += Allocas.size();
  80     Changed = true;
  81   }
  82
  83   return Changed;
  84 }
  85
  86 // createPromoteMemoryToRegister - Provide an entry point to create this pass.
  87 //
  88 FunctionPass *llvm::createPromoteMemoryToRegisterPass() {
  89   return new PromotePass();
  90 }