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merged 2 commits into from
Sep 27, 2023
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PR for llvm/llvm-project#66868 #705

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a2bc1c4
[SimpleLoopUnswitch] Fix reversed branch during condition injection
nikic Sep 20, 2023
33a141c
[SimpleLoopUnswitch] Fix exponential unswitch
nikic Sep 20, 2023
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61 changes: 34 additions & 27 deletions llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2126,9 +2126,10 @@ static void unswitchNontrivialInvariants(
Loop &L, Instruction &TI, ArrayRef<Value *> Invariants,
IVConditionInfo &PartialIVInfo, DominatorTree &DT, LoopInfo &LI,
AssumptionCache &AC,
function_ref<void(bool, bool, ArrayRef<Loop *>)> UnswitchCB,
function_ref<void(bool, bool, bool, ArrayRef<Loop *>)> UnswitchCB,
ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
function_ref<void(Loop &, StringRef)> DestroyLoopCB, bool InsertFreeze) {
function_ref<void(Loop &, StringRef)> DestroyLoopCB, bool InsertFreeze,
bool InjectedCondition) {
auto *ParentBB = TI.getParent();
BranchInst *BI = dyn_cast<BranchInst>(&TI);
SwitchInst *SI = BI ? nullptr : cast<SwitchInst>(&TI);
Expand Down Expand Up @@ -2581,7 +2582,7 @@ static void unswitchNontrivialInvariants(
for (Loop *UpdatedL : llvm::concat<Loop *>(NonChildClonedLoops, HoistedLoops))
if (UpdatedL->getParentLoop() == ParentL)
SibLoops.push_back(UpdatedL);
UnswitchCB(IsStillLoop, PartiallyInvariant, SibLoops);
UnswitchCB(IsStillLoop, PartiallyInvariant, InjectedCondition, SibLoops);

if (MSSAU && VerifyMemorySSA)
MSSAU->getMemorySSA()->verifyMemorySSA();
Expand Down Expand Up @@ -2979,13 +2980,6 @@ static bool shouldTryInjectInvariantCondition(
/// the metadata.
bool shouldTryInjectBasingOnMetadata(const BranchInst *BI,
const BasicBlock *TakenSucc) {
// Skip branches that have already been unswithed this way. After successful
// unswitching of injected condition, we will still have a copy of this loop
// which looks exactly the same as original one. To prevent the 2nd attempt
// of unswitching it in the same pass, mark this branch as "nothing to do
// here".
if (BI->hasMetadata("llvm.invariant.condition.injection.disabled"))
return false;
SmallVector<uint32_t> Weights;
if (!extractBranchWeights(*BI, Weights))
return false;
Expand Down Expand Up @@ -3060,7 +3054,6 @@ injectPendingInvariantConditions(NonTrivialUnswitchCandidate Candidate, Loop &L,
auto *InjectedCond =
ICmpInst::Create(Instruction::ICmp, Pred, LHS, RHS, "injected.cond",
Preheader->getTerminator());
auto *OldCond = TI->getCondition();

BasicBlock *CheckBlock = BasicBlock::Create(Ctx, BB->getName() + ".check",
BB->getParent(), InLoopSucc);
Expand All @@ -3069,12 +3062,9 @@ injectPendingInvariantConditions(NonTrivialUnswitchCandidate Candidate, Loop &L,
Builder.CreateCondBr(InjectedCond, InLoopSucc, CheckBlock);

Builder.SetInsertPoint(CheckBlock);
auto *NewTerm = Builder.CreateCondBr(OldCond, InLoopSucc, OutOfLoopSucc);

Builder.CreateCondBr(TI->getCondition(), TI->getSuccessor(0),
TI->getSuccessor(1));
TI->eraseFromParent();
// Prevent infinite unswitching.
NewTerm->setMetadata("llvm.invariant.condition.injection.disabled",
MDNode::get(BB->getContext(), {}));

// Fixup phis.
for (auto &I : *InLoopSucc) {
Expand Down Expand Up @@ -3442,7 +3432,7 @@ static bool shouldInsertFreeze(Loop &L, Instruction &TI, DominatorTree &DT,
static bool unswitchBestCondition(
Loop &L, DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC,
AAResults &AA, TargetTransformInfo &TTI,
function_ref<void(bool, bool, ArrayRef<Loop *>)> UnswitchCB,
function_ref<void(bool, bool, bool, ArrayRef<Loop *>)> UnswitchCB,
ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
function_ref<void(Loop &, StringRef)> DestroyLoopCB) {
// Collect all invariant conditions within this loop (as opposed to an inner
Expand All @@ -3452,9 +3442,10 @@ static bool unswitchBestCondition(
Instruction *PartialIVCondBranch = nullptr;
collectUnswitchCandidates(UnswitchCandidates, PartialIVInfo,
PartialIVCondBranch, L, LI, AA, MSSAU);
collectUnswitchCandidatesWithInjections(UnswitchCandidates, PartialIVInfo,
PartialIVCondBranch, L, DT, LI, AA,
MSSAU);
if (!findOptionMDForLoop(&L, "llvm.loop.unswitch.injection.disable"))
collectUnswitchCandidatesWithInjections(UnswitchCandidates, PartialIVInfo,
PartialIVCondBranch, L, DT, LI, AA,
MSSAU);
// If we didn't find any candidates, we're done.
if (UnswitchCandidates.empty())
return false;
Expand All @@ -3475,8 +3466,11 @@ static bool unswitchBestCondition(
return false;
}

if (Best.hasPendingInjection())
bool InjectedCondition = false;
if (Best.hasPendingInjection()) {
Best = injectPendingInvariantConditions(Best, L, DT, LI, AC, MSSAU);
InjectedCondition = true;
}
assert(!Best.hasPendingInjection() &&
"All injections should have been done by now!");

Expand Down Expand Up @@ -3504,7 +3498,7 @@ static bool unswitchBestCondition(
<< ") terminator: " << *Best.TI << "\n");
unswitchNontrivialInvariants(L, *Best.TI, Best.Invariants, PartialIVInfo, DT,
LI, AC, UnswitchCB, SE, MSSAU, DestroyLoopCB,
InsertFreeze);
InsertFreeze, InjectedCondition);
return true;
}

Expand Down Expand Up @@ -3533,7 +3527,7 @@ static bool
unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC,
AAResults &AA, TargetTransformInfo &TTI, bool Trivial,
bool NonTrivial,
function_ref<void(bool, bool, ArrayRef<Loop *>)> UnswitchCB,
function_ref<void(bool, bool, bool, ArrayRef<Loop *>)> UnswitchCB,
ScalarEvolution *SE, MemorySSAUpdater *MSSAU,
ProfileSummaryInfo *PSI, BlockFrequencyInfo *BFI,
function_ref<void(Loop &, StringRef)> DestroyLoopCB) {
Expand All @@ -3548,7 +3542,8 @@ unswitchLoop(Loop &L, DominatorTree &DT, LoopInfo &LI, AssumptionCache &AC,
if (Trivial && unswitchAllTrivialConditions(L, DT, LI, SE, MSSAU)) {
// If we unswitched successfully we will want to clean up the loop before
// processing it further so just mark it as unswitched and return.
UnswitchCB(/*CurrentLoopValid*/ true, false, {});
UnswitchCB(/*CurrentLoopValid*/ true, /*PartiallyInvariant*/ false,
/*InjectedCondition*/ false, {});
return true;
}

Expand Down Expand Up @@ -3644,6 +3639,7 @@ PreservedAnalyses SimpleLoopUnswitchPass::run(Loop &L, LoopAnalysisManager &AM,

auto UnswitchCB = [&L, &U, &LoopName](bool CurrentLoopValid,
bool PartiallyInvariant,
bool InjectedCondition,
ArrayRef<Loop *> NewLoops) {
// If we did a non-trivial unswitch, we have added new (cloned) loops.
if (!NewLoops.empty())
Expand All @@ -3663,6 +3659,16 @@ PreservedAnalyses SimpleLoopUnswitchPass::run(Loop &L, LoopAnalysisManager &AM,
Context, L.getLoopID(), {"llvm.loop.unswitch.partial"},
{DisableUnswitchMD});
L.setLoopID(NewLoopID);
} else if (InjectedCondition) {
// Do the same for injection of invariant conditions.
auto &Context = L.getHeader()->getContext();
MDNode *DisableUnswitchMD = MDNode::get(
Context,
MDString::get(Context, "llvm.loop.unswitch.injection.disable"));
MDNode *NewLoopID = makePostTransformationMetadata(
Context, L.getLoopID(), {"llvm.loop.unswitch.injection"},
{DisableUnswitchMD});
L.setLoopID(NewLoopID);
} else
U.revisitCurrentLoop();
} else
Expand Down Expand Up @@ -3755,6 +3761,7 @@ bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
auto *SE = SEWP ? &SEWP->getSE() : nullptr;

auto UnswitchCB = [&L, &LPM](bool CurrentLoopValid, bool PartiallyInvariant,
bool InjectedCondition,
ArrayRef<Loop *> NewLoops) {
// If we did a non-trivial unswitch, we have added new (cloned) loops.
for (auto *NewL : NewLoops)
Expand All @@ -3765,9 +3772,9 @@ bool SimpleLoopUnswitchLegacyPass::runOnLoop(Loop *L, LPPassManager &LPM) {
// but it is the best we can do in the old PM.
if (CurrentLoopValid) {
// If the current loop has been unswitched using a partially invariant
// condition, we should not re-add the current loop to avoid unswitching
// on the same condition again.
if (!PartiallyInvariant)
// condition or injected invariant condition, we should not re-add the
// current loop to avoid unswitching on the same condition again.
if (!PartiallyInvariant && !InjectedCondition)
LPM.addLoop(*L);
} else
LPM.markLoopAsDeleted(*L);
Expand Down
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