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[SCEV] Avoid unnecessary call to getExitingBlock() in computeExitLimit() #96188

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Merged
merged 2 commits into from
Jun 21, 2024
Merged

[SCEV] Avoid unnecessary call to getExitingBlock() in computeExitLimit() #96188

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ad57d93
[SCEV] Avoid unnecessary call to getExitingBlock() in computeExitLimit()
Enna1 Jun 20, 2024
c4a89de
address review comments
Enna1 Jun 20, 2024
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2 changes: 1 addition & 1 deletion llvm/include/llvm/Analysis/ScalarEvolution.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1766,7 +1766,7 @@ class ScalarEvolution {
/// this call will try to use a minimal set of SCEV predicates in order to
/// return an exact answer.
ExitLimit computeExitLimit(const Loop *L, BasicBlock *ExitingBlock,
bool AllowPredicates = false);
bool IsOnlyExit, bool AllowPredicates = false);

// Helper functions for computeExitLimitFromCond to avoid exponential time
// complexity.
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9 changes: 4 additions & 5 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Expand Up @@ -8775,6 +8775,7 @@ ScalarEvolution::computeBackedgeTakenCount(const Loop *L,
const SCEV *MustExitMaxBECount = nullptr;
const SCEV *MayExitMaxBECount = nullptr;
bool MustExitMaxOrZero = false;
bool IsOnlyExit = ExitingBlocks.size() == 1;

// Compute the ExitLimit for each loop exit. Use this to populate ExitCounts
// and compute maxBECount.
Expand All @@ -8792,7 +8793,7 @@ ScalarEvolution::computeBackedgeTakenCount(const Loop *L,
continue;
}

ExitLimit EL = computeExitLimit(L, ExitBB, AllowPredicates);
ExitLimit EL = computeExitLimit(L, ExitBB, IsOnlyExit, AllowPredicates);

assert((AllowPredicates || EL.Predicates.empty()) &&
"Predicated exit limit when predicates are not allowed!");
Expand Down Expand Up @@ -8867,15 +8868,14 @@ ScalarEvolution::computeBackedgeTakenCount(const Loop *L,

ScalarEvolution::ExitLimit
ScalarEvolution::computeExitLimit(const Loop *L, BasicBlock *ExitingBlock,
bool AllowPredicates) {
bool IsOnlyExit, bool AllowPredicates) {
assert(L->contains(ExitingBlock) && "Exit count for non-loop block?");
// If our exiting block does not dominate the latch, then its connection with
// loop's exit limit may be far from trivial.
const BasicBlock *Latch = L->getLoopLatch();
if (!Latch || !DT.dominates(ExitingBlock, Latch))
return getCouldNotCompute();

bool IsOnlyExit = (L->getExitingBlock() != nullptr);
Instruction *Term = ExitingBlock->getTerminator();
if (BranchInst *BI = dyn_cast<BranchInst>(Term)) {
assert(BI->isConditional() && "If unconditional, it can't be in loop!");
Expand All @@ -8899,8 +8899,7 @@ ScalarEvolution::computeExitLimit(const Loop *L, BasicBlock *ExitingBlock,
}
assert(Exit && "Exiting block must have at least one exit");
return computeExitLimitFromSingleExitSwitch(
L, SI, Exit,
/*ControlsOnlyExit=*/IsOnlyExit);
L, SI, Exit, /*ControlsOnlyExit=*/IsOnlyExit);
}

return getCouldNotCompute();
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