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/Compiler.h"
  30 #include "llvm/Support/CFG.h"
  31 #include <list>
  32 using namespace llvm;
  33
  34 STATISTIC(NumRegsDemoted, "Number of registers demoted");
  35 STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
  36
  37 namespace {
  38   struct VISIBILITY_HIDDEN RegToMem : public FunctionPass {
  39     static char ID; // Pass identification, replacement for typeid
  40     RegToMem() : FunctionPass(&ID) {}
  41
  42     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  43       AU.addRequiredID(BreakCriticalEdgesID);
  44       AU.addPreservedID(BreakCriticalEdgesID);
  45     }
  46
  47    bool valueEscapes(Instruction* i) {
  48       BasicBlock* bb = i->getParent();
  49       for (Value::use_iterator ii = i->use_begin(), ie = i->use_end();
  50            ii != ie; ++ii)
  51         if (cast<Instruction>(*ii)->getParent() != bb ||
  52             isa<PHINode>(*ii))
  53           return true;
  54       return false;
  55     }
  56
  57     virtual bool runOnFunction(Function &F) {
  58       if (!F.isDeclaration()) {
  59         // Insert all new allocas into entry block.
  60         BasicBlock* BBEntry = &F.getEntryBlock();
  61         assert(pred_begin(BBEntry) == pred_end(BBEntry) &&
  62                "Entry block to function must not have predecessors!");
  63
  64         // Find first non-alloca instruction and create insertion point. This is
  65         // safe if block is well-formed: it always have terminator, otherwise
  66         // we'll get and assertion.
  67         BasicBlock::iterator I = BBEntry->begin();
  68         while (isa<AllocaInst>(I)) ++I;
  69
  70         CastInst *AllocaInsertionPoint =
  71           CastInst::Create(Instruction::BitCast,
  72                       Constant::getNullValue(Type::Int32Ty), Type::Int32Ty,
  73                            "reg2mem alloca point", I);
  74
  75         // Find the escaped instructions. But don't create stack slots for
  76         // allocas in entry block.
  77         std::list<Instruction*> worklist;
  78         for (Function::iterator ibb = F.begin(), ibe = F.end();
  79              ibb != ibe; ++ibb)
  80           for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
  81                iib != iie; ++iib) {
  82             if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
  83                 valueEscapes(iib)) {
  84               worklist.push_front(&*iib);
  85             }
  86           }
  87
  88         // Demote escaped instructions
  89         NumRegsDemoted += worklist.size();
  90         for (std::list<Instruction*>::iterator ilb = worklist.begin(),
  91                ile = worklist.end(); ilb != ile; ++ilb)
  92           DemoteRegToStack(**ilb, false, AllocaInsertionPoint);
  93
  94         worklist.clear();
  95
  96         // Find all phi's
  97         for (Function::iterator ibb = F.begin(), ibe = F.end();
  98              ibb != ibe; ++ibb)
  99           for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
 100                iib != iie; ++iib)
 101             if (isa<PHINode>(iib))
 102               worklist.push_front(&*iib);
 103
 104         // Demote phi nodes
 105         NumPhisDemoted += worklist.size();
 106         for (std::list<Instruction*>::iterator ilb = worklist.begin(),
 107                ile = worklist.end(); ilb != ile; ++ilb)
 108           DemotePHIToStack(cast<PHINode>(*ilb), AllocaInsertionPoint);
 109
 110         return true;
 111       }
 112       return false;
 113     }
 114   };
 115 }
 116
 117 char RegToMem::ID = 0;
 118 static RegisterPass<RegToMem>
 119 X("reg2mem", "Demote all values to stack slots");
 120
 121 // createDemoteRegisterToMemory - Provide an entry point to create this pass.
 122 //
 123 const PassInfo *const llvm::DemoteRegisterToMemoryID = &X;
 124 FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
 125   return new RegToMem();
 126 }