Reg2Mem.cpp revision 1997473cf72957d0e70322e2fe6fe2ab141c58a6 
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#define DEBUG_TYPE "reg2mem"
20#include "llvm/Transforms/Scalar.h"
21#include "llvm/Transforms/Utils/Local.h"
22#include "llvm/Pass.h"
23#include "llvm/Function.h"
24#include "llvm/Module.h"
25#include "llvm/BasicBlock.h"
26#include "llvm/Instructions.h"
27#include "llvm/ADT/Statistic.h"
28#include "llvm/Support/Compiler.h"
29#include <list>
30using namespace llvm;
31
32STATISTIC(NumDemoted, "Number of registers demoted");
33
34namespace {
35  struct VISIBILITY_HIDDEN RegToMem : public FunctionPass {
36    static char ID; // Pass identifcation, replacement for typeid
37    RegToMem() : FunctionPass((intptr_t)&ID) {}
38
39    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
40      AU.addRequiredID(BreakCriticalEdgesID);
41      AU.addPreservedID(BreakCriticalEdgesID);
42    }
43
44   bool valueEscapes(Instruction* i) {
45      BasicBlock* bb = i->getParent();
46      for(Value::use_iterator ii = i->use_begin(), ie = i->use_end();
47          ii != ie; ++ii)
48        if (cast<Instruction>(*ii)->getParent() != bb ||
49            isa<PHINode>(*ii))
50          return true;
51      return false;
52    }
53
54    virtual bool runOnFunction(Function &F) {
55      if (!F.isDeclaration()) {
56        //give us a clean block
57        BasicBlock* bbold = &F.getEntryBlock();
58        BasicBlock* bbnew = new BasicBlock("allocablock", &F, &F.getEntryBlock());
59        new BranchInst(bbold, bbnew);
60
61        //find the instructions
62        std::list<Instruction*> worklist;
63        for (Function::iterator ibb = F.begin(), ibe = F.end();
64             ibb != ibe; ++ibb)
65          for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
66               iib != iie; ++iib) {
67            if(valueEscapes(iib))
68              worklist.push_front(&*iib);
69          }
70        //demote escaped instructions
71        NumDemoted += worklist.size();
72        for (std::list<Instruction*>::iterator ilb = worklist.begin(),
73               ile = worklist.end(); ilb != ile; ++ilb)
74          DemoteRegToStack(**ilb, false);
75        return true;
76      }
77      return false;
78    }
79  };
80
81  char RegToMem::ID = 0;
82  RegisterPass<RegToMem> X("reg2mem", "Demote all values to stack slots");
83}
84
85// createDemoteRegisterToMemory - Provide an entry point to create this pass.
86//
87const PassInfo *llvm::DemoteRegisterToMemoryID = X.getPassInfo();
88FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
89  return new RegToMem();
90}
91