Reg2Mem.cpp revision 99b8e26b84033b5932cfe2a1d1542ea33cb21a8a 
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
30using namespace llvm;
31
32namespace {
33  Statistic<> NumDemoted("reg2mem", "Number of registers demoted");
34
35  struct RegToMem : public FunctionPass {
36
37   bool valueEscapes(Instruction* i) {
38      BasicBlock* bb = i->getParent();
39      for(Value::use_iterator ii = i->use_begin(), ie = i->use_end();
40          ii != ie; ++ii)
41        if (cast<Instruction>(*ii)->getParent() != bb)
42          return true;
43      return false;
44    }
45
46    virtual bool runOnFunction(Function &F) {
47      if (!F.isExternal()) {
48        //give us a clean block
49	BasicBlock* bbold = &F.getEntryBlock();
50	BasicBlock* bbnew = new BasicBlock("allocablock", &F, &F.getEntryBlock());
51	new BranchInst(bbold, bbnew);
52
53        //find the instructions
54        std::list<Instruction*> worklist;
55        for (Function::iterator ibb = F.begin(), ibe = F.end();
56             ibb != ibe; ++ibb)
57          for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
58               iib != iie; ++iib) {
59            if(valueEscapes(iib))
60              worklist.push_front(&*iib);
61          }
62        //demote escaped instructions
63        NumDemoted += worklist.size();
64        for (std::list<Instruction*>::iterator ilb = worklist.begin(),
65               ile = worklist.end(); ilb != ile; ++ilb)
66          DemoteRegToStack(**ilb, false);
67        return true;
68      }
69      return false;
70    }
71  };
72
73  RegisterOpt<RegToMem> X("reg2mem", "Demote all values to stack slots");
74}
75
76// createDemoteRegisterToMemory - Provide an entry point to create this pass.
77//
78FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
79  return new RegToMem();
80}
81