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