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