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//===- Reg2Mem.cpp - Convert registers to allocas -------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file demotes all registers to memory references. It is intented to be
// the inverse of PromoteMemoryToRegister. By converting to loads, the only
// values live accross basic blocks are allocas and loads before phi nodes.
// It is intended that this should make CFG hacking much easier.
// To make later hacking easier, the entry block is split into two, such that
// all introduced allocas and nothing else are in the entry block.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "reg2mem"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Pass.h"
#include "llvm/Function.h"
#include "llvm/LLVMContext.h"
#include "llvm/Module.h"
#include "llvm/BasicBlock.h"
#include "llvm/Instructions.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/CFG.h"
#include <list>
using namespace llvm;
STATISTIC(NumRegsDemoted, "Number of registers demoted");
STATISTIC(NumPhisDemoted, "Number of phi-nodes demoted");
namespace {
struct VISIBILITY_HIDDEN RegToMem : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
RegToMem() : FunctionPass(&ID) {}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequiredID(BreakCriticalEdgesID);
AU.addPreservedID(BreakCriticalEdgesID);
}
bool valueEscapes(Instruction* i) {
BasicBlock* bb = i->getParent();
for (Value::use_iterator ii = i->use_begin(), ie = i->use_end();
ii != ie; ++ii)
if (cast<Instruction>(*ii)->getParent() != bb ||
isa<PHINode>(*ii))
return true;
return false;
}
virtual bool runOnFunction(Function &F) {
if (!F.isDeclaration()) {
// Insert all new allocas into entry block.
BasicBlock* BBEntry = &F.getEntryBlock();
assert(pred_begin(BBEntry) == pred_end(BBEntry) &&
"Entry block to function must not have predecessors!");
// Find first non-alloca instruction and create insertion point. This is
// safe if block is well-formed: it always have terminator, otherwise
// we'll get and assertion.
BasicBlock::iterator I = BBEntry->begin();
while (isa<AllocaInst>(I)) ++I;
CastInst *AllocaInsertionPoint =
CastInst::Create(Instruction::BitCast,
F.getContext().getNullValue(Type::Int32Ty), Type::Int32Ty,
"reg2mem alloca point", I);
// Find the escaped instructions. But don't create stack slots for
// allocas in entry block.
std::list<Instruction*> worklist;
for (Function::iterator ibb = F.begin(), ibe = F.end();
ibb != ibe; ++ibb)
for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
iib != iie; ++iib) {
if (!(isa<AllocaInst>(iib) && iib->getParent() == BBEntry) &&
valueEscapes(iib)) {
worklist.push_front(&*iib);
}
}
// Demote escaped instructions
NumRegsDemoted += worklist.size();
for (std::list<Instruction*>::iterator ilb = worklist.begin(),
ile = worklist.end(); ilb != ile; ++ilb)
DemoteRegToStack(**ilb, false, AllocaInsertionPoint);
worklist.clear();
// Find all phi's
for (Function::iterator ibb = F.begin(), ibe = F.end();
ibb != ibe; ++ibb)
for (BasicBlock::iterator iib = ibb->begin(), iie = ibb->end();
iib != iie; ++iib)
if (isa<PHINode>(iib))
worklist.push_front(&*iib);
// Demote phi nodes
NumPhisDemoted += worklist.size();
for (std::list<Instruction*>::iterator ilb = worklist.begin(),
ile = worklist.end(); ilb != ile; ++ilb)
DemotePHIToStack(cast<PHINode>(*ilb), AllocaInsertionPoint);
return true;
}
return false;
}
};
}
char RegToMem::ID = 0;
static RegisterPass<RegToMem>
X("reg2mem", "Demote all values to stack slots");
// createDemoteRegisterToMemory - Provide an entry point to create this pass.
//
const PassInfo *const llvm::DemoteRegisterToMemoryID = &X;
FunctionPass *llvm::createDemoteRegisterToMemoryPass() {
return new RegToMem();
}
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