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[RISCV] Adjust unroll prefs for loops with vectors #151525

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Merged
merged 1 commit into from
Jul 31, 2025
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[RISCV] Adjust unroll prefs for loops with vectors #151525

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15 changes: 7 additions & 8 deletions llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2627,18 +2627,17 @@ void RISCVTTIImpl::getUnrollingPreferences(
if (L->getNumBlocks() > 4)
return;

// Don't unroll vectorized loops, including the remainder loop
if (getBooleanLoopAttribute(L, "llvm.loop.isvectorized"))
return;

// Scan the loop: don't unroll loops with calls as this could prevent
// inlining.
// inlining. Don't unroll auto-vectorized loops either, though do allow
// unrolling of the scalar remainder.
bool IsVectorized = getBooleanLoopAttribute(L, "llvm.loop.isvectorized");
InstructionCost Cost = 0;
for (auto *BB : L->getBlocks()) {
for (auto &I : *BB) {
// Initial setting - Don't unroll loops containing vectorized
// instructions.
if (I.getType()->isVectorTy())
// Both auto-vectorized loops and the scalar remainder have the
// isvectorized attribute, so differentiate between them by the presence
// of vector instructions.
if (IsVectorized && I.getType()->isVectorTy())
return;
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Thanks for introducing this enhancement!

It would help if the code would could add an attribute or a field to the Loop instance that this is actually the "remainder of a loop that has isvectorized attribute. This way any later-on check, for example in a target-specific tuning, would leverage the same without re-iterating over each and every instruction in the loop.

@fhahn


if (isa<CallInst>(I) || isa<InvokeInst>(I)) {
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