#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "sink"
STATISTIC(NumSunk, "Number of instructions sunk");
STATISTIC(NumSinkIter, "Number of sinking iterations");
namespace {
class Sinking : public FunctionPass {
DominatorTree *DT;
LoopInfo *LI;
AliasAnalysis *AA;
const DataLayout *DL;
public:
static char ID; Sinking() : FunctionPass(ID) {
initializeSinkingPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
FunctionPass::getAnalysisUsage(AU);
AU.addRequired<AliasAnalysis>();
AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<LoopInfo>();
AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<LoopInfo>();
}
private:
bool ProcessBlock(BasicBlock &BB);
bool SinkInstruction(Instruction *I, SmallPtrSet<Instruction *, 8> &Stores);
bool AllUsesDominatedByBlock(Instruction *Inst, BasicBlock *BB) const;
bool IsAcceptableTarget(Instruction *Inst, BasicBlock *SuccToSinkTo) const;
};
}
char Sinking::ID = 0;
INITIALIZE_PASS_BEGIN(Sinking, "sink", "Code sinking", false, false)
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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 (Use &U : Inst->uses()) {
Instruction *UseInst = cast<Instruction>(U.getUser());
BasicBlock *UseBlock = UseInst->getParent();
if (PHINode *PN = dyn_cast<PHINode>(UseInst)) {
unsigned Num = PHINode::getIncomingValueNumForOperand(U.getOperandNo());
UseBlock = PN->getIncomingBlock(Num);
}
if (!DT->dominates(BB, UseBlock))
return false;
}
return true;
}
bool Sinking::runOnFunction(Function &F) {
DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LI = &getAnalysis<LoopInfo>();
AA = &getAnalysis<AliasAnalysis>();
DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
DL = DLP ? &DLP->getDataLayout() : nullptr;
bool MadeChange, EverMadeChange = false;
do {
MadeChange = false;
DEBUG(dbgs() << "Sinking iteration " << NumSinkIter << "\n");
for (Function::iterator I = F.begin(), E = F.end();
I != E; ++I)
MadeChange |= ProcessBlock(*I);
EverMadeChange |= MadeChange;
NumSinkIter++;
} while (MadeChange);
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::IsAcceptableTarget(Instruction *Inst,
BasicBlock *SuccToSinkTo) const {
assert(Inst && "Instruction to be sunk is null");
assert(SuccToSinkTo && "Candidate sink target is null");
if (Inst->getParent() == SuccToSinkTo)
return false;
if (SuccToSinkTo->getUniquePredecessor() != Inst->getParent()) {
if (!isSafeToSpeculativelyExecute(Inst, DL))
return false;
if (!DT->dominates(Inst->getParent(), SuccToSinkTo))
return false;
Loop *succ = LI->getLoopFor(SuccToSinkTo);
Loop *cur = LI->getLoopFor(Inst->getParent());
if (succ != nullptr && succ != cur)
return false;
}
return AllUsesDominatedByBlock(Inst, SuccToSinkTo);
}
bool Sinking::SinkInstruction(Instruction *Inst,
SmallPtrSet<Instruction *, 8> &Stores) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(Inst))
if (AI->isStaticAlloca())
return false;
if (!isSafeToMove(Inst, AA, Stores))
return false;
BasicBlock *SuccToSinkTo = nullptr;
DomTreeNode *DTN = DT->getNode(Inst->getParent());
for (DomTreeNode::iterator I = DTN->begin(), E = DTN->end();
I != E && SuccToSinkTo == nullptr; ++I) {
BasicBlock *Candidate = (*I)->getBlock();
if ((*I)->getIDom()->getBlock() == Inst->getParent() &&
IsAcceptableTarget(Inst, Candidate))
SuccToSinkTo = Candidate;
}
for (succ_iterator I = succ_begin(Inst->getParent()),
E = succ_end(Inst->getParent()); I != E && !SuccToSinkTo; ++I) {
if (IsAcceptableTarget(Inst, *I))
SuccToSinkTo = *I;
}
if (!SuccToSinkTo)
return false;
DEBUG(dbgs() << "Sink" << *Inst << " (";
Inst->getParent()->printAsOperand(dbgs(), false);
dbgs() << " -> ";
SuccToSinkTo->printAsOperand(dbgs(), false);
dbgs() << ")\n");
Inst->moveBefore(SuccToSinkTo->getFirstInsertionPt());
return true;
}