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[LV] Consider EVL legality for TTI tail folding preference #144790

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Merged
merged 2 commits into from
Jun 19, 2025
Merged

[LV] Consider EVL legality for TTI tail folding preference #144790

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fe476ab
[LV] Consider EVL legality for TTI tail folding preference
preames Jun 18, 2025
6c24b06
Merge branch 'main' into pr-lv-evl-check-after-tti
preames Jun 19, 2025
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43 changes: 20 additions & 23 deletions llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1364,36 +1364,33 @@ class LoopVectorizationCostModel {
return;
}

if (!ForceTailFoldingStyle.getNumOccurrences()) {
ChosenTailFoldingStyle = {
TTI.getPreferredTailFoldingStyle(/*IVUpdateMayOverflow=*/true),
TTI.getPreferredTailFoldingStyle(/*IVUpdateMayOverflow=*/false)};
return;
}
// Default to TTI preference, but allow command line override.
ChosenTailFoldingStyle = {
TTI.getPreferredTailFoldingStyle(/*IVUpdateMayOverflow=*/true),
TTI.getPreferredTailFoldingStyle(/*IVUpdateMayOverflow=*/false)};
Comment on lines +1368 to +1370
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Need a test for this change, I assume

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There is no way to test this with in tree backends.

if (ForceTailFoldingStyle.getNumOccurrences())
ChosenTailFoldingStyle = {ForceTailFoldingStyle.getValue(),
ForceTailFoldingStyle.getValue()};

// Set styles when forced.
ChosenTailFoldingStyle = {ForceTailFoldingStyle.getValue(),
ForceTailFoldingStyle.getValue()};
if (ForceTailFoldingStyle != TailFoldingStyle::DataWithEVL)
return;
// Override forced styles if needed.
// FIXME: Investigate opportunity for fixed vector factor.
bool EVLIsLegal = UserIC <= 1 && IsScalableVF &&
TTI.hasActiveVectorLength() && !EnableVPlanNativePath;
if (!EVLIsLegal) {
// If for some reason EVL mode is unsupported, fallback to
// DataWithoutLaneMask to try to vectorize the loop with folded tail
// in a generic way.
ChosenTailFoldingStyle = {TailFoldingStyle::DataWithoutLaneMask,
TailFoldingStyle::DataWithoutLaneMask};
LLVM_DEBUG(
dbgs()
<< "LV: Preference for VP intrinsics indicated. Will "
"not try to generate VP Intrinsics "
<< (UserIC > 1
? "since interleave count specified is greater than 1.\n"
: "due to non-interleaving reasons.\n"));
}
if (EVLIsLegal)
return;
// If for some reason EVL mode is unsupported, fallback to
// DataWithoutLaneMask to try to vectorize the loop with folded tail
// in a generic way.
ChosenTailFoldingStyle = {TailFoldingStyle::DataWithoutLaneMask,
TailFoldingStyle::DataWithoutLaneMask};
LLVM_DEBUG(
dbgs() << "LV: Preference for VP intrinsics indicated. Will "
"not try to generate VP Intrinsics "
<< (UserIC > 1
? "since interleave count specified is greater than 1.\n"
: "due to non-interleaving reasons.\n"));
}

/// Returns true if all loop blocks should be masked to fold tail loop.
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