mirror of
https://github.com/RPCS3/llvm-mirror.git
synced 2024-12-12 05:56:28 +00:00
Reimplement heuristic for estimating complete-unroll optimization effects.
Summary: This patch reimplements heuristic that tries to estimate optimization beneftis from complete loop unrolling. In this patch I kept the minimal changes - e.g. I removed code handling branches and folding compares. That's a promising area, but now there are too many questions to discuss before we can enable it. Test Plan: Tests are included in the patch. Reviewers: hfinkel, chandlerc Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D8816 llvm-svn: 237156
This commit is contained in:
Michael Zolotukhin
parent
bd0b851f88
commit
56e82e59ff
@ -186,33 +186,21 @@ namespace {
|
||||
void selectThresholds(const Loop *L, bool HasPragma,
|
||||
const TargetTransformInfo::UnrollingPreferences &UP,
|
||||
unsigned &Threshold, unsigned &PartialThreshold,
|
||||
unsigned NumberOfOptimizedInstructions) {
|
||||
unsigned &AbsoluteThreshold,
|
||||
unsigned &PercentOfOptimizedForCompleteUnroll) {
|
||||
// Determine the current unrolling threshold. While this is
|
||||
// normally set from UnrollThreshold, it is overridden to a
|
||||
// smaller value if the current function is marked as
|
||||
// optimize-for-size, and the unroll threshold was not user
|
||||
// specified.
|
||||
Threshold = UserThreshold ? CurrentThreshold : UP.Threshold;
|
||||
|
||||
// If we are allowed to completely unroll if we can remove M% of
|
||||
// instructions, and we know that with complete unrolling we'll be able
|
||||
// to kill N instructions, then we can afford to completely unroll loops
|
||||
// with unrolled size up to N*100/M.
|
||||
// Adjust the threshold according to that:
|
||||
unsigned PercentOfOptimizedForCompleteUnroll =
|
||||
UserPercentOfOptimized ? CurrentMinPercentOfOptimized
|
||||
: UP.MinPercentOfOptimized;
|
||||
unsigned AbsoluteThreshold = UserAbsoluteThreshold
|
||||
? CurrentAbsoluteThreshold
|
||||
: UP.AbsoluteThreshold;
|
||||
if (PercentOfOptimizedForCompleteUnroll)
|
||||
Threshold = std::max<unsigned>(Threshold,
|
||||
NumberOfOptimizedInstructions * 100 /
|
||||
PercentOfOptimizedForCompleteUnroll);
|
||||
// But don't allow unrolling loops bigger than absolute threshold.
|
||||
Threshold = std::min<unsigned>(Threshold, AbsoluteThreshold);
|
||||
|
||||
PartialThreshold = UserThreshold ? CurrentThreshold : UP.PartialThreshold;
|
||||
AbsoluteThreshold = UserAbsoluteThreshold ? CurrentAbsoluteThreshold
|
||||
: UP.AbsoluteThreshold;
|
||||
PercentOfOptimizedForCompleteUnroll = UserPercentOfOptimized
|
||||
? CurrentMinPercentOfOptimized
|
||||
: UP.MinPercentOfOptimized;
|
||||
|
||||
if (!UserThreshold &&
|
||||
L->getHeader()->getParent()->hasFnAttribute(
|
||||
Attribute::OptimizeForSize)) {
|
||||
@ -231,6 +219,10 @@ namespace {
|
||||
std::max<unsigned>(PartialThreshold, PragmaUnrollThreshold);
|
||||
}
|
||||
}
|
||||
bool canUnrollCompletely(Loop *L, unsigned Threshold,
|
||||
unsigned AbsoluteThreshold, uint64_t UnrolledSize,
|
||||
unsigned NumberOfOptimizedInstructions,
|
||||
unsigned PercentOfOptimizedForCompleteUnroll);
|
||||
};
|
||||
}
|
||||
|
||||
@ -253,57 +245,75 @@ Pass *llvm::createSimpleLoopUnrollPass() {
|
||||
return llvm::createLoopUnrollPass(-1, -1, 0, 0);
|
||||
}
|
||||
|
||||
static bool isLoadFromConstantInitializer(Value *V) {
|
||||
if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
|
||||
if (GV->isConstant() && GV->hasDefinitiveInitializer())
|
||||
return GV->getInitializer();
|
||||
return false;
|
||||
}
|
||||
|
||||
namespace {
|
||||
/// \brief SCEV expressions visitor used for finding expressions that would
|
||||
/// become constants if the loop L is unrolled.
|
||||
struct FindConstantPointers {
|
||||
bool LoadCanBeConstantFolded;
|
||||
/// \brief Shows whether the expression is ConstAddress+Constant or not.
|
||||
bool IndexIsConstant;
|
||||
APInt Step;
|
||||
APInt StartValue;
|
||||
Value *BaseAddress;
|
||||
const Loop *L;
|
||||
ScalarEvolution &SE;
|
||||
FindConstantPointers(const Loop *loop, ScalarEvolution &SE)
|
||||
: LoadCanBeConstantFolded(true), IndexIsConstant(true), L(loop), SE(SE) {}
|
||||
|
||||
/// \brief Used for filtering out SCEV expressions with two or more AddRec
|
||||
/// subexpressions.
|
||||
///
|
||||
/// Used to filter out complicated SCEV expressions, having several AddRec
|
||||
/// sub-expressions. We don't handle them, because unrolling one loop
|
||||
/// would help to replace only one of these inductions with a constant, and
|
||||
/// consequently, the expression would remain non-constant.
|
||||
bool HaveSeenAR;
|
||||
|
||||
/// \brief If the SCEV expression becomes ConstAddress+Constant, this value
|
||||
/// holds ConstAddress. Otherwise, it's nullptr.
|
||||
Value *BaseAddress;
|
||||
|
||||
/// \brief The loop, which we try to completely unroll.
|
||||
const Loop *L;
|
||||
|
||||
ScalarEvolution &SE;
|
||||
|
||||
FindConstantPointers(const Loop *L, ScalarEvolution &SE)
|
||||
: IndexIsConstant(true), HaveSeenAR(false), BaseAddress(nullptr),
|
||||
L(L), SE(SE) {}
|
||||
|
||||
/// Examine the given expression S and figure out, if it can be a part of an
|
||||
/// expression, that could become a constant after the loop is unrolled.
|
||||
/// The routine sets IndexIsConstant and HaveSeenAR according to the analysis
|
||||
/// results.
|
||||
/// \returns true if we need to examine subexpressions, and false otherwise.
|
||||
bool follow(const SCEV *S) {
|
||||
if (const SCEVUnknown *SC = dyn_cast<SCEVUnknown>(S)) {
|
||||
// We've reached the leaf node of SCEV, it's most probably just a
|
||||
// variable. Now it's time to see if it corresponds to a global constant
|
||||
// global (in which case we can eliminate the load), or not.
|
||||
// variable.
|
||||
// If it's the only one SCEV-subexpression, then it might be a base
|
||||
// address of an index expression.
|
||||
// If we've already recorded base address, then just give up on this SCEV
|
||||
// - it's too complicated.
|
||||
if (BaseAddress) {
|
||||
IndexIsConstant = false;
|
||||
return false;
|
||||
}
|
||||
BaseAddress = SC->getValue();
|
||||
LoadCanBeConstantFolded =
|
||||
IndexIsConstant && isLoadFromConstantInitializer(BaseAddress);
|
||||
return false;
|
||||
}
|
||||
if (isa<SCEVConstant>(S))
|
||||
return true;
|
||||
return false;
|
||||
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(S)) {
|
||||
// If the current SCEV expression is AddRec, and its loop isn't the loop
|
||||
// we are about to unroll, then we won't get a constant address after
|
||||
// unrolling, and thus, won't be able to eliminate the load.
|
||||
if (AR->getLoop() != L)
|
||||
return IndexIsConstant = false;
|
||||
// If the step isn't constant, we won't get constant addresses in unrolled
|
||||
// version. Bail out.
|
||||
if (const SCEVConstant *StepSE =
|
||||
dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
|
||||
Step = StepSE->getValue()->getValue();
|
||||
else
|
||||
return IndexIsConstant = false;
|
||||
|
||||
return IndexIsConstant;
|
||||
if (AR->getLoop() != L) {
|
||||
IndexIsConstant = false;
|
||||
return false;
|
||||
}
|
||||
// We don't handle multiple AddRecs here, so give up in this case.
|
||||
if (HaveSeenAR) {
|
||||
IndexIsConstant = false;
|
||||
return false;
|
||||
}
|
||||
HaveSeenAR = true;
|
||||
}
|
||||
// If Result is true, continue traversal.
|
||||
// Otherwise, we have found something that prevents us from (possible) load
|
||||
// elimination.
|
||||
return IndexIsConstant;
|
||||
|
||||
// Continue traversal.
|
||||
return true;
|
||||
}
|
||||
bool isDone() const { return !IndexIsConstant; }
|
||||
};
|
||||
@ -328,27 +338,54 @@ class UnrollAnalyzer : public InstVisitor<UnrollAnalyzer, bool> {
|
||||
typedef InstVisitor<UnrollAnalyzer, bool> Base;
|
||||
friend class InstVisitor<UnrollAnalyzer, bool>;
|
||||
|
||||
struct SCEVGEPDescriptor {
|
||||
Value *BaseAddr;
|
||||
APInt Start;
|
||||
APInt Step;
|
||||
};
|
||||
|
||||
/// \brief The loop we're going to analyze.
|
||||
const Loop *L;
|
||||
|
||||
/// \brief TripCount of the given loop.
|
||||
unsigned TripCount;
|
||||
|
||||
ScalarEvolution &SE;
|
||||
|
||||
const TargetTransformInfo &TTI;
|
||||
|
||||
// While we walk the loop instructions, we we build up and maintain a mapping
|
||||
// of simplified values specific to this iteration. The idea is to propagate
|
||||
// any special information we have about loads that can be replaced with
|
||||
// constants after complete unrolling, and account for likely simplifications
|
||||
// post-unrolling.
|
||||
DenseMap<Value *, Constant *> SimplifiedValues;
|
||||
DenseMap<LoadInst *, Value *> LoadBaseAddresses;
|
||||
SmallPtrSet<Instruction *, 32> CountedInstructions;
|
||||
|
||||
/// \brief Count the number of optimized instructions.
|
||||
unsigned NumberOfOptimizedInstructions;
|
||||
// To avoid requesting SCEV info on every iteration, request it once, and
|
||||
// for each value that would become ConstAddress+Constant after loop
|
||||
// unrolling, save the corresponding data.
|
||||
SmallDenseMap<Value *, SCEVGEPDescriptor> SCEVCache;
|
||||
|
||||
// Provide base case for our instruction visit.
|
||||
/// \brief Number of currently simulated iteration.
|
||||
///
|
||||
/// If an expression is ConstAddress+Constant, then the Constant is
|
||||
/// Start + Iteration*Step, where Start and Step could be obtained from
|
||||
/// SCEVCache.
|
||||
unsigned Iteration;
|
||||
|
||||
/// \brief Upper threshold for complete unrolling.
|
||||
unsigned MaxUnrolledLoopSize;
|
||||
|
||||
/// Base case for the instruction visitor.
|
||||
bool visitInstruction(Instruction &I) { return false; };
|
||||
// TODO: We should also visit ICmp, FCmp, GetElementPtr, Trunc, ZExt, SExt,
|
||||
// FPTrunc, FPExt, FPToUI, FPToSI, UIToFP, SIToFP, BitCast, Select,
|
||||
// ExtractElement, InsertElement, ShuffleVector, ExtractValue, InsertValue.
|
||||
//
|
||||
// Probaly it's worth to hoist the code for estimating the simplifications
|
||||
// effects to a separate class, since we have a very similar code in
|
||||
// InlineCost already.
|
||||
|
||||
/// TODO: Add visitors for other instruction types, e.g. ZExt, SExt.
|
||||
|
||||
/// Try to simplify binary operator I.
|
||||
///
|
||||
/// TODO: Probaly it's worth to hoist the code for estimating the
|
||||
/// simplifications effects to a separate class, since we have a very similar
|
||||
/// code in InlineCost already.
|
||||
bool visitBinaryOperator(BinaryOperator &I) {
|
||||
Value *LHS = I.getOperand(0), *RHS = I.getOperand(1);
|
||||
if (!isa<Constant>(LHS))
|
||||
@ -365,7 +402,7 @@ class UnrollAnalyzer : public InstVisitor<UnrollAnalyzer, bool> {
|
||||
else
|
||||
SimpleV = SimplifyBinOp(I.getOpcode(), LHS, RHS, DL);
|
||||
|
||||
if (SimpleV && CountedInstructions.insert(&I).second)
|
||||
if (SimpleV)
|
||||
NumberOfOptimizedInstructions += TTI.getUserCost(&I);
|
||||
|
||||
if (Constant *C = dyn_cast_or_null<Constant>(SimpleV)) {
|
||||
@ -375,207 +412,172 @@ class UnrollAnalyzer : public InstVisitor<UnrollAnalyzer, bool> {
|
||||
return false;
|
||||
}
|
||||
|
||||
Constant *computeLoadValue(LoadInst *LI, unsigned Iteration) {
|
||||
if (!LI)
|
||||
return nullptr;
|
||||
Value *BaseAddr = LoadBaseAddresses[LI];
|
||||
if (!BaseAddr)
|
||||
return nullptr;
|
||||
/// Try to fold load I.
|
||||
bool visitLoad(LoadInst &I) {
|
||||
Value *AddrOp = I.getPointerOperand();
|
||||
if (!isa<Constant>(AddrOp))
|
||||
if (Constant *SimplifiedAddrOp = SimplifiedValues.lookup(AddrOp))
|
||||
AddrOp = SimplifiedAddrOp;
|
||||
|
||||
auto GV = dyn_cast<GlobalVariable>(BaseAddr);
|
||||
if (!GV)
|
||||
return nullptr;
|
||||
auto It = SCEVCache.find(AddrOp);
|
||||
if (It == SCEVCache.end())
|
||||
return false;
|
||||
SCEVGEPDescriptor GEPDesc = It->second;
|
||||
|
||||
auto GV = dyn_cast<GlobalVariable>(GEPDesc.BaseAddr);
|
||||
// We're only interested in loads that can be completely folded to a
|
||||
// constant.
|
||||
if (!GV || !GV->hasInitializer())
|
||||
return false;
|
||||
|
||||
ConstantDataSequential *CDS =
|
||||
dyn_cast<ConstantDataSequential>(GV->getInitializer());
|
||||
if (!CDS)
|
||||
return nullptr;
|
||||
|
||||
const SCEV *BaseAddrSE = SE.getSCEV(BaseAddr);
|
||||
const SCEV *S = SE.getSCEV(LI->getPointerOperand());
|
||||
const SCEV *OffSE = SE.getMinusSCEV(S, BaseAddrSE);
|
||||
|
||||
APInt StepC, StartC;
|
||||
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(OffSE);
|
||||
if (!AR)
|
||||
return nullptr;
|
||||
|
||||
if (const SCEVConstant *StepSE =
|
||||
dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE)))
|
||||
StepC = StepSE->getValue()->getValue();
|
||||
else
|
||||
return nullptr;
|
||||
|
||||
if (const SCEVConstant *StartSE = dyn_cast<SCEVConstant>(AR->getStart()))
|
||||
StartC = StartSE->getValue()->getValue();
|
||||
else
|
||||
return nullptr;
|
||||
return false;
|
||||
|
||||
// Check possible overflow.
|
||||
if (GEPDesc.Start.getActiveBits() > 32 || GEPDesc.Step.getActiveBits() > 32)
|
||||
return false;
|
||||
unsigned ElemSize = CDS->getElementType()->getPrimitiveSizeInBits() / 8U;
|
||||
unsigned Start = StartC.getLimitedValue();
|
||||
unsigned Step = StepC.getLimitedValue();
|
||||
|
||||
unsigned Index = (Start + Step * Iteration) / ElemSize;
|
||||
if (Index >= CDS->getNumElements())
|
||||
return nullptr;
|
||||
uint64_t Index = (GEPDesc.Start.getLimitedValue() +
|
||||
GEPDesc.Step.getLimitedValue() * Iteration) /
|
||||
ElemSize;
|
||||
if (Index >= CDS->getNumElements()) {
|
||||
// FIXME: For now we conservatively ignore out of bound accesses, but
|
||||
// we're allowed to perform the optimization in this case.
|
||||
return false;
|
||||
}
|
||||
|
||||
Constant *CV = CDS->getElementAsConstant(Index);
|
||||
assert(CV && "Constant expected.");
|
||||
SimplifiedValues[&I] = CV;
|
||||
|
||||
return CV;
|
||||
NumberOfOptimizedInstructions += TTI.getUserCost(&I);
|
||||
return true;
|
||||
}
|
||||
|
||||
public:
|
||||
UnrollAnalyzer(const Loop *L, unsigned TripCount, ScalarEvolution &SE,
|
||||
const TargetTransformInfo &TTI)
|
||||
: L(L), TripCount(TripCount), SE(SE), TTI(TTI),
|
||||
NumberOfOptimizedInstructions(0) {}
|
||||
|
||||
// Visit all loads the loop L, and for those that, after complete loop
|
||||
// unrolling, would have a constant address and it will point to a known
|
||||
// constant initializer, record its base address for future use. It is used
|
||||
// when we estimate number of potentially simplified instructions.
|
||||
void findConstFoldableLoads() {
|
||||
/// Visit all GEPs in the loop and find those which after complete loop
|
||||
/// unrolling would become a constant, or BaseAddress+Constant.
|
||||
///
|
||||
/// Such GEPs could allow to evaluate a load to a constant later - for now we
|
||||
/// just store the corresponding BaseAddress and StartValue with StepValue in
|
||||
/// the SCEVCache.
|
||||
void cacheSCEVResults() {
|
||||
for (auto BB : L->getBlocks()) {
|
||||
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
|
||||
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
|
||||
if (!LI->isSimple())
|
||||
continue;
|
||||
Value *AddrOp = LI->getPointerOperand();
|
||||
const SCEV *S = SE.getSCEV(AddrOp);
|
||||
for (Instruction &I : *BB) {
|
||||
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(&I)) {
|
||||
Value *V = cast<Value>(GEP);
|
||||
if (!SE.isSCEVable(V->getType()))
|
||||
continue;
|
||||
const SCEV *S = SE.getSCEV(V);
|
||||
// FIXME: Hoist the initialization out of the loop.
|
||||
FindConstantPointers Visitor(L, SE);
|
||||
SCEVTraversal<FindConstantPointers> T(Visitor);
|
||||
// Try to find (BaseAddress+Step+Offset) tuple.
|
||||
// If succeeded, save it to the cache - it might help in folding
|
||||
// loads.
|
||||
T.visitAll(S);
|
||||
if (Visitor.IndexIsConstant && Visitor.LoadCanBeConstantFolded) {
|
||||
LoadBaseAddresses[LI] = Visitor.BaseAddress;
|
||||
}
|
||||
if (!Visitor.IndexIsConstant || !Visitor.BaseAddress)
|
||||
continue;
|
||||
|
||||
const SCEV *BaseAddrSE = SE.getSCEV(Visitor.BaseAddress);
|
||||
if (BaseAddrSE->getType() != S->getType())
|
||||
continue;
|
||||
const SCEV *OffSE = SE.getMinusSCEV(S, BaseAddrSE);
|
||||
const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(OffSE);
|
||||
|
||||
if (!AR)
|
||||
continue;
|
||||
|
||||
const SCEVConstant *StepSE =
|
||||
dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE));
|
||||
const SCEVConstant *StartSE = dyn_cast<SCEVConstant>(AR->getStart());
|
||||
if (!StepSE || !StartSE)
|
||||
continue;
|
||||
|
||||
SCEVCache[V] = {Visitor.BaseAddress, StartSE->getValue()->getValue(),
|
||||
StepSE->getValue()->getValue()};
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// Given a list of loads that could be constant-folded (LoadBaseAddresses),
|
||||
// estimate number of optimized instructions after substituting the concrete
|
||||
// values for the given Iteration. Also track how many instructions become
|
||||
// dead through this process.
|
||||
unsigned estimateNumberOfOptimizedInstructions(unsigned Iteration) {
|
||||
// We keep a set vector for the worklist so that we don't wast space in the
|
||||
// worklist queuing up the same instruction repeatedly. This can happen due
|
||||
// to multiple operands being the same instruction or due to the same
|
||||
// instruction being an operand of lots of things that end up dead or
|
||||
// simplified.
|
||||
SmallSetVector<Instruction *, 8> Worklist;
|
||||
public:
|
||||
UnrollAnalyzer(const Loop *L, unsigned TripCount, ScalarEvolution &SE,
|
||||
const TargetTransformInfo &TTI, unsigned MaxUnrolledLoopSize)
|
||||
: L(L), TripCount(TripCount), SE(SE), TTI(TTI),
|
||||
MaxUnrolledLoopSize(MaxUnrolledLoopSize),
|
||||
NumberOfOptimizedInstructions(0), UnrolledLoopSize(0) {}
|
||||
|
||||
// Clear the simplified values and counts for this iteration.
|
||||
SimplifiedValues.clear();
|
||||
CountedInstructions.clear();
|
||||
NumberOfOptimizedInstructions = 0;
|
||||
/// \brief Count the number of optimized instructions.
|
||||
unsigned NumberOfOptimizedInstructions;
|
||||
|
||||
// We start by adding all loads to the worklist.
|
||||
for (auto &LoadDescr : LoadBaseAddresses) {
|
||||
LoadInst *LI = LoadDescr.first;
|
||||
SimplifiedValues[LI] = computeLoadValue(LI, Iteration);
|
||||
if (CountedInstructions.insert(LI).second)
|
||||
NumberOfOptimizedInstructions += TTI.getUserCost(LI);
|
||||
/// \brief Count the total number of instructions.
|
||||
unsigned UnrolledLoopSize;
|
||||
|
||||
for (User *U : LI->users())
|
||||
Worklist.insert(cast<Instruction>(U));
|
||||
}
|
||||
/// \brief Figure out if the loop is worth full unrolling.
|
||||
///
|
||||
/// Complete loop unrolling can make some loads constant, and we need to know
|
||||
/// if that would expose any further optimization opportunities. This routine
|
||||
/// estimates this optimization. It assigns computed number of instructions,
|
||||
/// that potentially might be optimized away, to
|
||||
/// NumberOfOptimizedInstructions, and total number of instructions to
|
||||
/// UnrolledLoopSize (not counting blocks that won't be reached, if we were
|
||||
/// able to compute the condition).
|
||||
/// \returns false if we can't analyze the loop, or if we discovered that
|
||||
/// unrolling won't give anything. Otherwise, returns true.
|
||||
bool analyzeLoop() {
|
||||
SmallSetVector<BasicBlock *, 16> BBWorklist;
|
||||
|
||||
// And then we try to simplify every user of every instruction from the
|
||||
// worklist. If we do simplify a user, add it to the worklist to process
|
||||
// its users as well.
|
||||
while (!Worklist.empty()) {
|
||||
Instruction *I = Worklist.pop_back_val();
|
||||
if (!L->contains(I))
|
||||
continue;
|
||||
if (!visit(I))
|
||||
continue;
|
||||
for (User *U : I->users())
|
||||
Worklist.insert(cast<Instruction>(U));
|
||||
}
|
||||
// Don't simulate loops with a big or unknown tripcount
|
||||
if (!UnrollMaxIterationsCountToAnalyze || !TripCount ||
|
||||
TripCount > UnrollMaxIterationsCountToAnalyze)
|
||||
return false;
|
||||
|
||||
// Now that we know the potentially simplifed instructions, estimate number
|
||||
// of instructions that would become dead if we do perform the
|
||||
// simplification.
|
||||
// To avoid compute SCEV-expressions on every iteration, compute them once
|
||||
// and store interesting to us in SCEVCache.
|
||||
cacheSCEVResults();
|
||||
|
||||
// The dead instructions are held in a separate set. This is used to
|
||||
// prevent us from re-examining instructions and make sure we only count
|
||||
// the benifit once. The worklist's internal set handles insertion
|
||||
// deduplication.
|
||||
SmallPtrSet<Instruction *, 16> DeadInstructions;
|
||||
// Simulate execution of each iteration of the loop counting instructions,
|
||||
// which would be simplified.
|
||||
// Since the same load will take different values on different iterations,
|
||||
// we literally have to go through all loop's iterations.
|
||||
for (Iteration = 0; Iteration < TripCount; ++Iteration) {
|
||||
SimplifiedValues.clear();
|
||||
BBWorklist.clear();
|
||||
BBWorklist.insert(L->getHeader());
|
||||
// Note that we *must not* cache the size, this loop grows the worklist.
|
||||
for (unsigned Idx = 0; Idx != BBWorklist.size(); ++Idx) {
|
||||
BasicBlock *BB = BBWorklist[Idx];
|
||||
|
||||
// Lambda to enque operands onto the worklist.
|
||||
auto EnqueueOperands = [&](Instruction &I) {
|
||||
for (auto *Op : I.operand_values())
|
||||
if (auto *OpI = dyn_cast<Instruction>(Op))
|
||||
if (!OpI->use_empty())
|
||||
Worklist.insert(OpI);
|
||||
};
|
||||
// Visit all instructions in the given basic block and try to simplify
|
||||
// it. We don't change the actual IR, just count optimization
|
||||
// opportunities.
|
||||
for (Instruction &I : *BB) {
|
||||
UnrolledLoopSize += TTI.getUserCost(&I);
|
||||
Base::visit(I);
|
||||
// If unrolled body turns out to be too big, bail out.
|
||||
if (UnrolledLoopSize - NumberOfOptimizedInstructions >
|
||||
MaxUnrolledLoopSize)
|
||||
return false;
|
||||
}
|
||||
|
||||
// Start by initializing worklist with simplified instructions.
|
||||
for (auto &FoldedKeyValue : SimplifiedValues)
|
||||
if (auto *FoldedInst = dyn_cast<Instruction>(FoldedKeyValue.first)) {
|
||||
DeadInstructions.insert(FoldedInst);
|
||||
|
||||
// Add each instruction operand of this dead instruction to the
|
||||
// worklist.
|
||||
EnqueueOperands(*FoldedInst);
|
||||
// Add BB's successors to the worklist.
|
||||
for (BasicBlock *Succ : successors(BB))
|
||||
if (L->contains(Succ))
|
||||
BBWorklist.insert(Succ);
|
||||
}
|
||||
|
||||
// If a definition of an insn is only used by simplified or dead
|
||||
// instructions, it's also dead. Check defs of all instructions from the
|
||||
// worklist.
|
||||
while (!Worklist.empty()) {
|
||||
Instruction *I = Worklist.pop_back_val();
|
||||
if (!L->contains(I))
|
||||
continue;
|
||||
if (DeadInstructions.count(I))
|
||||
continue;
|
||||
|
||||
if (std::all_of(I->user_begin(), I->user_end(), [&](User *U) {
|
||||
return DeadInstructions.count(cast<Instruction>(U));
|
||||
})) {
|
||||
NumberOfOptimizedInstructions += TTI.getUserCost(I);
|
||||
DeadInstructions.insert(I);
|
||||
EnqueueOperands(*I);
|
||||
}
|
||||
// If we found no optimization opportunities on the first iteration, we
|
||||
// won't find them on later ones too.
|
||||
if (!NumberOfOptimizedInstructions)
|
||||
return false;
|
||||
}
|
||||
return NumberOfOptimizedInstructions;
|
||||
return true;
|
||||
}
|
||||
};
|
||||
} // namespace
|
||||
|
||||
// Complete loop unrolling can make some loads constant, and we need to know if
|
||||
// that would expose any further optimization opportunities.
|
||||
// This routine estimates this optimization effect and returns the number of
|
||||
// instructions, that potentially might be optimized away.
|
||||
static unsigned
|
||||
approximateNumberOfOptimizedInstructions(const Loop *L, ScalarEvolution &SE,
|
||||
unsigned TripCount,
|
||||
const TargetTransformInfo &TTI) {
|
||||
if (!TripCount || !UnrollMaxIterationsCountToAnalyze)
|
||||
return 0;
|
||||
|
||||
UnrollAnalyzer UA(L, TripCount, SE, TTI);
|
||||
UA.findConstFoldableLoads();
|
||||
|
||||
// Estimate number of instructions, that could be simplified if we replace a
|
||||
// load with the corresponding constant. Since the same load will take
|
||||
// different values on different iterations, we have to go through all loop's
|
||||
// iterations here. To limit ourselves here, we check only first N
|
||||
// iterations, and then scale the found number, if necessary.
|
||||
unsigned IterationsNumberForEstimate =
|
||||
std::min<unsigned>(UnrollMaxIterationsCountToAnalyze, TripCount);
|
||||
unsigned NumberOfOptimizedInstructions = 0;
|
||||
for (unsigned i = 0; i < IterationsNumberForEstimate; ++i)
|
||||
NumberOfOptimizedInstructions +=
|
||||
UA.estimateNumberOfOptimizedInstructions(i);
|
||||
|
||||
NumberOfOptimizedInstructions *= TripCount / IterationsNumberForEstimate;
|
||||
|
||||
return NumberOfOptimizedInstructions;
|
||||
}
|
||||
|
||||
/// ApproximateLoopSize - Approximate the size of the loop.
|
||||
static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls,
|
||||
bool &NotDuplicatable,
|
||||
@ -679,6 +681,49 @@ static void SetLoopAlreadyUnrolled(Loop *L) {
|
||||
L->setLoopID(NewLoopID);
|
||||
}
|
||||
|
||||
bool LoopUnroll::canUnrollCompletely(
|
||||
Loop *L, unsigned Threshold, unsigned AbsoluteThreshold,
|
||||
uint64_t UnrolledSize, unsigned NumberOfOptimizedInstructions,
|
||||
unsigned PercentOfOptimizedForCompleteUnroll) {
|
||||
|
||||
if (Threshold == NoThreshold) {
|
||||
DEBUG(dbgs() << " Can fully unroll, because no threshold is set.\n");
|
||||
return true;
|
||||
}
|
||||
|
||||
if (UnrolledSize <= Threshold) {
|
||||
DEBUG(dbgs() << " Can fully unroll, because unrolled size: "
|
||||
<< UnrolledSize << "<" << Threshold << "\n");
|
||||
return true;
|
||||
}
|
||||
|
||||
assert(UnrolledSize && "UnrolledSize can't be 0 at this point.");
|
||||
unsigned PercentOfOptimizedInstructions =
|
||||
(uint64_t)NumberOfOptimizedInstructions * 100ull / UnrolledSize;
|
||||
|
||||
if (UnrolledSize <= AbsoluteThreshold &&
|
||||
PercentOfOptimizedInstructions >= PercentOfOptimizedForCompleteUnroll) {
|
||||
DEBUG(dbgs() << " Can fully unroll, because unrolling will help removing "
|
||||
<< PercentOfOptimizedInstructions
|
||||
<< "% instructions (threshold: "
|
||||
<< PercentOfOptimizedForCompleteUnroll << "%)\n");
|
||||
DEBUG(dbgs() << " Unrolled size (" << UnrolledSize
|
||||
<< ") is less than the threshold (" << AbsoluteThreshold
|
||||
<< ").\n");
|
||||
return true;
|
||||
}
|
||||
|
||||
DEBUG(dbgs() << " Too large to fully unroll:\n");
|
||||
DEBUG(dbgs() << " Unrolled size: " << UnrolledSize << "\n");
|
||||
DEBUG(dbgs() << " Estimated number of optimized instructions: "
|
||||
<< NumberOfOptimizedInstructions << "\n");
|
||||
DEBUG(dbgs() << " Absolute threshold: " << AbsoluteThreshold << "\n");
|
||||
DEBUG(dbgs() << " Minimum percent of removed instructions: "
|
||||
<< PercentOfOptimizedForCompleteUnroll << "\n");
|
||||
DEBUG(dbgs() << " Threshold for small loops: " << Threshold << "\n");
|
||||
return false;
|
||||
}
|
||||
|
||||
unsigned LoopUnroll::selectUnrollCount(
|
||||
const Loop *L, unsigned TripCount, bool PragmaFullUnroll,
|
||||
unsigned PragmaCount, const TargetTransformInfo::UnrollingPreferences &UP,
|
||||
@ -785,27 +830,34 @@ bool LoopUnroll::runOnLoop(Loop *L, LPPassManager &LPM) {
|
||||
return false;
|
||||
}
|
||||
|
||||
unsigned NumberOfOptimizedInstructions =
|
||||
approximateNumberOfOptimizedInstructions(L, *SE, TripCount, TTI);
|
||||
DEBUG(dbgs() << " Complete unrolling could save: "
|
||||
<< NumberOfOptimizedInstructions << "\n");
|
||||
|
||||
unsigned Threshold, PartialThreshold;
|
||||
unsigned AbsoluteThreshold, PercentOfOptimizedForCompleteUnroll;
|
||||
selectThresholds(L, HasPragma, UP, Threshold, PartialThreshold,
|
||||
NumberOfOptimizedInstructions);
|
||||
AbsoluteThreshold, PercentOfOptimizedForCompleteUnroll);
|
||||
|
||||
// Given Count, TripCount and thresholds determine the type of
|
||||
// unrolling which is to be performed.
|
||||
enum { Full = 0, Partial = 1, Runtime = 2 };
|
||||
int Unrolling;
|
||||
if (TripCount && Count == TripCount) {
|
||||
if (Threshold != NoThreshold && UnrolledSize > Threshold) {
|
||||
DEBUG(dbgs() << " Too large to fully unroll with count: " << Count
|
||||
<< " because size: " << UnrolledSize << ">" << Threshold
|
||||
<< "\n");
|
||||
Unrolling = Partial;
|
||||
} else {
|
||||
Unrolling = Partial;
|
||||
// If the loop is really small, we don't need to run an expensive analysis.
|
||||
if (canUnrollCompletely(
|
||||
L, Threshold, AbsoluteThreshold,
|
||||
UnrolledSize, 0, 100)) {
|
||||
Unrolling = Full;
|
||||
} else {
|
||||
// The loop isn't that small, but we still can fully unroll it if that
|
||||
// helps to remove a significant number of instructions.
|
||||
// To check that, run additional analysis on the loop.
|
||||
UnrollAnalyzer UA(L, TripCount, *SE, TTI, AbsoluteThreshold);
|
||||
if (UA.analyzeLoop() &&
|
||||
canUnrollCompletely(L, Threshold, AbsoluteThreshold,
|
||||
UA.UnrolledLoopSize,
|
||||
UA.NumberOfOptimizedInstructions,
|
||||
PercentOfOptimizedForCompleteUnroll)) {
|
||||
Unrolling = Full;
|
||||
}
|
||||
}
|
||||
} else if (TripCount && Count < TripCount) {
|
||||
Unrolling = Partial;
|
||||
|
||||
34
test/Transforms/LoopUnroll/full-unroll-bad-geps.ll
Normal file
34
test/Transforms/LoopUnroll/full-unroll-bad-geps.ll
Normal file
@ -0,0 +1,34 @@
|
||||
; Check that we don't crash on corner cases.
|
||||
; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-absolute-threshold=10 -unroll-threshold=10 -unroll-percent-of-optimized-for-complete-unroll=20 -o /dev/null
|
||||
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
|
||||
|
||||
define void @foo1() {
|
||||
entry:
|
||||
br label %for.body
|
||||
|
||||
for.body:
|
||||
%phi = phi i64 [ 0, %entry ], [ %inc, %for.body ]
|
||||
%idx = zext i32 undef to i64
|
||||
%add.ptr = getelementptr inbounds i64, i64* null, i64 %idx
|
||||
%inc = add nuw nsw i64 %phi, 1
|
||||
%cmp = icmp ult i64 %inc, 999
|
||||
br i1 %cmp, label %for.body, label %for.exit
|
||||
|
||||
for.exit:
|
||||
ret void
|
||||
}
|
||||
|
||||
define void @foo2() {
|
||||
entry:
|
||||
br label %for.body
|
||||
|
||||
for.body:
|
||||
%phi = phi i64 [ 0, %entry ], [ %inc, %for.body ]
|
||||
%x = getelementptr i32, <4 x i32*> undef, <4 x i32> <i32 1, i32 1, i32 1, i32 1>
|
||||
%inc = add nuw nsw i64 %phi, 1
|
||||
%cmp = icmp ult i64 %inc, 999
|
||||
br i1 %cmp, label %for.body, label %for.exit
|
||||
|
||||
for.exit:
|
||||
ret void
|
||||
}
|
||||
@ -17,8 +17,8 @@
|
||||
; optimizations to remove ~55% of the instructions, the loop body size is 9,
|
||||
; and unrolled size is 65.
|
||||
|
||||
; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-absolute-threshold=10 -unroll-threshold=10 -unroll-percent-of-optimized-for-complete-unroll=30 | FileCheck %s -check-prefix=TEST1
|
||||
; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-absolute-threshold=100 -unroll-threshold=10 -unroll-percent-of-optimized-for-complete-unroll=30 | FileCheck %s -check-prefix=TEST2
|
||||
; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-absolute-threshold=10 -unroll-threshold=10 -unroll-percent-of-optimized-for-complete-unroll=20 | FileCheck %s -check-prefix=TEST1
|
||||
; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-absolute-threshold=100 -unroll-threshold=10 -unroll-percent-of-optimized-for-complete-unroll=20 | FileCheck %s -check-prefix=TEST2
|
||||
; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-absolute-threshold=100 -unroll-threshold=10 -unroll-percent-of-optimized-for-complete-unroll=80 | FileCheck %s -check-prefix=TEST3
|
||||
; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=1000 -unroll-absolute-threshold=100 -unroll-threshold=100 -unroll-percent-of-optimized-for-complete-unroll=80 | FileCheck %s -check-prefix=TEST4
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user