lib/Transforms/Scalar/Reg2Mem.cpp

   1 //===- Reg2Mem.cpp - Convert registers to allocas -------------------------===//
   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 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/LLVMContext.h"
  25 #include "llvm/Module.h"
  26 #include "llvm/BasicBlock.h"
  27 #include "llvm/Instructions.h"
  28 #include "llvm/ADT/Statistic.h"
  29 #include "llvm/Support/CFG.h"
  30 #include <list>
  31 using namespace llvm;
  32
  33 STATISTIC(NumRegsDemoted, "Number of registers demoted");
  34 STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
  35
  36 namespace {
  37   struct RegToMem : public FunctionPass {
  38     static char ID; // Pass identification, replacement for typeid
  39     RegToMem() : FunctionPass(ID) {
  40       initializeRegToMemPass(*PassRegistry::getPassRegistry());
  41     }
  42
  43     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  44       AU.addRequiredID(BreakCriticalEdgesID);
  45       AU.addPreservedID(BreakCriticalEdgesID);
  46     }
  47
  48    bool valueEscapes(const Instruction *Inst) const {
  49      const BasicBlock *BB = Inst->getParent();
  50       for (Value::const_use_iterator UI = Inst->use_begin(),E = Inst->use_end();
  51            UI != E; ++UI) {
  52         const Instruction *I = cast<Instruction>(*UI);
  53         if (I->getParent() != BB || isa<PHINode>(I))
  54           return true;
  55       }
  56       return false;
  57     }
  58
  59     virtual bool runOnFunction(Function &F);
  60   };
  61 }
  62
  63 char RegToMem::ID = 0;
  64 INITIALIZE_PASS_BEGIN(RegToMem, "reg2mem", "Demote all values to stack slots",
  65                 false, false)
  66 INITIALIZE_PASS_DEPENDENCY(BreakCriticalEdges)
  67 INITIALIZE_PASS_END(RegToMem, "reg2mem", "Demote all values to stack slots",
  68                 false, false)
  69
  70 bool RegToMem::runOnFunction(Function &F) {
  71   if (F.isDeclaration())
  72     return false;
  73
  74   // Insert all new allocas into entry block.
  75   BasicBlock *BBEntry = &F.getEntryBlock();
  76   assert(pred_begin(BBEntry) == pred_end(BBEntry) &&
  77          "Entry block to function must not have predecessors!");
  78
  79   // Find first non-alloca instruction and create insertion point. This is
  80   // safe if block is well-formed: it always have terminator, otherwise
  81   // we'll get and assertion.
  82   BasicBlock::iterator I = BBEntry->begin();
  83   while (isa<AllocaInst>(I)) ++I;
  84
  85   CastInst *AllocaInsertionPoint =
  86     new BitCastInst(Constant::getNullValue(Type::getInt32Ty(F.getContext())),
  87                     Type::getInt32Ty(F.getContext()),
  88                     "reg2mem alloca point", I);
  89
  90   // Find the escaped instructions. But don't create stack slots for
  91   // allocas in entry block.
  92   std::list<Instruction*> WorkList;
  93   for (Function::iterator ibb = F.begin(), ibe = F.end();
  94        ibb != ibe; ++ibb)
  95     for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
  96          iib != iie; ++iib) {
  97       if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
  98           valueEscapes(iib)) {
  99         WorkList.push_front(&*iib);
 100       }
 101     }
 102
 103   // Demote escaped instructions
 104   NumRegsDemoted += WorkList.size();
 105   for (std::list<Instruction*>::iterator ilb = WorkList.begin(),
 106        ile = WorkList.end(); ilb != ile; ++ilb)
 107     DemoteRegToStack(**ilb, false, AllocaInsertionPoint);
 108
 109   WorkList.clear();
 110
 111   // Find all phi's
 112   for (Function::iterator ibb = F.begin(), ibe = F.end();
 113        ibb != ibe; ++ibb)
 114     for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
 115          iib != iie; ++iib)
 116       if (isa<PHINode>(iib))
 117         WorkList.push_front(&*iib);
 118
 119   // Demote phi nodes
 120   NumPhisDemoted += WorkList.size();
 121   for (std::list<Instruction*>::iterator ilb = WorkList.begin(),
 122        ile = WorkList.end(); ilb != ile; ++ilb)
 123     DemotePHIToStack(cast<PHINode>(*ilb), AllocaInsertionPoint);
 124
 125   return true;
 126 }
 127
 128
 129 // createDemoteRegisterToMemory - Provide an entry point to create this pass.
 130 //
 131 char &llvm::DemoteRegisterToMemoryID = RegToMem::ID;
 132 FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
 133   return new RegToMem();
 134 }