#define DEBUG_TYPE "sink"
#include "llvm/Transforms/Scalar.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Assembly/Writer.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
STATISTIC(NumSunk, "Number of instructions sunk");
namespace {
class Sinking : public FunctionPass {
DominatorTree *DT;
LoopInfo *LI;
AliasAnalysis *AA;
public:
static char ID; Sinking() : FunctionPass(ID) {
initializeSinkingPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
FunctionPass::getAnalysisUsage(AU);
AU.addRequired<AliasAnalysis>();
AU.addRequired<DominatorTree>();
AU.addRequired<LoopInfo>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<LoopInfo>();
}
private:
bool ProcessBlock(BasicBlock &BB);
bool SinkInstruction(Instruction *I, SmallPtrSet<Instruction *, 8> &Stores);
bool AllUsesDominatedByBlock(Instruction *Inst, BasicBlock *BB) const;
};
}
char Sinking::ID = 0;
INITIALIZE_PASS_BEGIN(Sinking, "sink", "Code sinking", false, false)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_END(Sinking, "sink", "Code sinking", false, false)
FunctionPass *llvm::createSinkingPass() { return new Sinking(); }
bool Sinking::AllUsesDominatedByBlock(Instruction *Inst,
BasicBlock *BB) const {
for (Value::use_iterator I = Inst->use_begin(),
E = Inst->use_end(); I != E; ++I) {
Instruction *UseInst = cast<Instruction>(*I);
BasicBlock *UseBlock = UseInst->getParent();
if (PHINode *PN = dyn_cast<PHINode>(UseInst)) {
unsigned Num = PHINode::getIncomingValueNumForOperand(I.getOperandNo());
UseBlock = PN->getIncomingBlock(Num);
}
if (!DT->dominates(BB, UseBlock))
return false;
}
return true;
}
bool Sinking::runOnFunction(Function &F) {
DT = &getAnalysis<DominatorTree>();
LI = &getAnalysis<LoopInfo>();
AA = &getAnalysis<AliasAnalysis>();
bool EverMadeChange = false;
while (1) {
bool MadeChange = false;
for (Function::iterator I = F.begin(), E = F.end();
I != E; ++I)
MadeChange |= ProcessBlock(*I);
if (!MadeChange) break;
EverMadeChange = true;
}
return EverMadeChange;
}
bool Sinking::ProcessBlock(BasicBlock &BB) {
if (BB.getTerminator()->getNumSuccessors() <= 1 || BB.empty()) return false;
if (!DT->isReachableFromEntry(&BB)) return false;
bool MadeChange = false;
BasicBlock::iterator I = BB.end();
--I;
bool ProcessedBegin = false;
SmallPtrSet<Instruction *, 8> Stores;
do {
Instruction *Inst = I;
ProcessedBegin = I == BB.begin();
if (!ProcessedBegin)
--I;
if (isa<DbgInfoIntrinsic>(Inst))
continue;
if (SinkInstruction(Inst, Stores))
++NumSunk, MadeChange = true;
} while (!ProcessedBegin);
return MadeChange;
}
static bool isSafeToMove(Instruction *Inst, AliasAnalysis *AA,
SmallPtrSet<Instruction *, 8> &Stores) {
if (Inst->mayWriteToMemory()) {
Stores.insert(Inst);
return false;
}
if (LoadInst *L = dyn_cast<LoadInst>(Inst)) {
AliasAnalysis::Location Loc = AA->getLocation(L);
for (SmallPtrSet<Instruction *, 8>::iterator I = Stores.begin(),
E = Stores.end(); I != E; ++I)
if (AA->getModRefInfo(*I, Loc) & AliasAnalysis::Mod)
return false;
}
if (isa<TerminatorInst>(Inst) || isa<PHINode>(Inst))
return false;
return true;
}
bool Sinking::SinkInstruction(Instruction *Inst,
SmallPtrSet<Instruction *, 8> &Stores) {
if (!isSafeToMove(Inst, AA, Stores))
return false;
BasicBlock *ParentBlock = Inst->getParent();
BasicBlock *SuccToSinkTo = 0;
for (succ_iterator SI = succ_begin(ParentBlock),
E = succ_end(ParentBlock); SI != E; ++SI) {
if (AllUsesDominatedByBlock(Inst, *SI)) {
SuccToSinkTo = *SI;
break;
}
}
if (SuccToSinkTo == 0)
return false;
if (Inst->getParent() == SuccToSinkTo)
return false;
DEBUG(dbgs() << "Sink instr " << *Inst);
DEBUG(dbgs() << "to block ";
WriteAsOperand(dbgs(), SuccToSinkTo, false));
if (SuccToSinkTo->getUniquePredecessor() != ParentBlock) {
if (!isSafeToSpeculativelyExecute(Inst)) {
DEBUG(dbgs() << " *** PUNTING: Wont sink load along critical edge.\n");
return false;
}
if (!DT->dominates(ParentBlock, SuccToSinkTo)) {
DEBUG(dbgs() << " *** PUNTING: Critical edge found\n");
return false;
}
if (LI->isLoopHeader(SuccToSinkTo)) {
DEBUG(dbgs() << " *** PUNTING: Loop header found\n");
return false;
}
DEBUG(dbgs() << "Sinking along critical edge.\n");
}
BasicBlock::iterator InsertPos = SuccToSinkTo->begin();
while (InsertPos != SuccToSinkTo->end() && isa<PHINode>(InsertPos))
++InsertPos;
Inst->moveBefore(InsertPos);
return true;
}