Reg2Mem.cpp revision ac0b6ae358944ae8b2b5a11dc08f52c3ed89f2da 
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    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  RegisterPass<RegToMem> X("reg2mem", "Demote all values to stack slots");
80}
81
82// createDemoteRegisterToMemory - Provide an entry point to create this pass.
83//
84const PassInfo *llvm::DemoteRegisterToMemoryID = X.getPassInfo();
85FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
86  return new RegToMem();
87}
88