lib/Transforms/Scalar/Reg2Mem.cpp

   1 //===- Reg2Mem.cpp - Convert registers to allocas -------------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file was developed by the LLVM research group and is distributed under
   6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file demotes all registers to memory references.  It is intented to be
  11 // the inverse of PromoteMemoryToRegister.  By converting to loads, the only
  12 // values live accross basic blocks are allocas and loads before phi nodes.
  13 // It is intended that this should make CFG hacking much easier.
  14 // To make later hacking easier, the entry block is split into two, such that
  15 // all introduced allocas and nothing else are in the entry block.
  16 //
  17 //===----------------------------------------------------------------------===//
  18
  19 #include "llvm/Transforms/Scalar.h"
  20 #include "llvm/Transforms/Utils/Local.h"
  21 #include "llvm/Pass.h"
  22 #include "llvm/Function.h"
  23 #include "llvm/Module.h"
  24 #include "llvm/BasicBlock.h"
  25 #include "llvm/Instructions.h"
  26 #include "llvm/ADT/Statistic.h"
  27
  28 #include <list>
  29
  30 using namespace llvm;
  31
  32 namespace {
  33   Statistic<> NumDemoted("reg2mem", "Number of registers demoted");
  34
  35   struct RegToMem : public FunctionPass {
  36
  37     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  38       AU.addRequiredID(BreakCriticalEdgesID);
  39       AU.addPreservedID(BreakCriticalEdgesID);
  40     }
  41
  42    bool valueEscapes(Instruction* i) {
  43       BasicBlock* bb = i->getParent();
  44       for(Value::use_iterator ii = i->use_begin(), ie = i->use_end();
  45           ii != ie; ++ii)
  46         if (cast<Instruction>(*ii)->getParent() != bb ||
  47             isa<PHINode>(*ii))
  48           return true;
  49       return false;
  50     }
  51
  52     virtual bool runOnFunction(Function &F) {
  53       if (!F.isExternal()) {
  54         //give us a clean block
  55         BasicBlock* bbold = &F.getEntryBlock();
  56         BasicBlock* bbnew = new BasicBlock("allocablock", &F, &F.getEntryBlock());
  57         new BranchInst(bbold, bbnew);
  58
  59         //find the instructions
  60         std::list<Instruction*> worklist;
  61         for (Function::iterator ibb = F.begin(), ibe = F.end();
  62              ibb != ibe; ++ibb)
  63           for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
  64                iib != iie; ++iib) {
  65             if(valueEscapes(iib))
  66               worklist.push_front(&*iib);
  67           }
  68         //demote escaped instructions
  69         NumDemoted += worklist.size();
  70         for (std::list<Instruction*>::iterator ilb = worklist.begin(),
  71                ile = worklist.end(); ilb != ile; ++ilb)
  72           DemoteRegToStack(**ilb, false);
  73         return true;
  74       }
  75       return false;
  76     }
  77   };
  78
  79   RegisterOpt<RegToMem> X("reg2mem", "Demote all values to stack slots");
  80 }
  81
  82 // createDemoteRegisterToMemory - Provide an entry point to create this pass.
  83 //
  84 const PassInfo *llvm::DemoteRegisterToMemoryID = X.getPassInfo();
  85 FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
  86   return new RegToMem();
  87 }