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[LV] Restructure handling of -prefer-predicate-over-epilogue option [NFC] 

This should be purely non-functional.  When touching this code for another reason, I found the handling of the PredicateOrDontVectorize piece here very confusing.  Let's make it an explicit state (instead of an implicit combination of two variables), and use early return for options/hint processing.
This commit is contained in:
Philip Reames 2020-12-15 12:33:51 -08:00
parent c103f9ef5a
commit a81db8b315
1 changed files with 31 additions and 18 deletions
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49
llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -1201,7 +1201,10 @@ enum ScalarEpilogueLowering {
CM_ScalarEpilogueNotAllowedLowTripLoop,
// Loop hint predicate indicating an epilogue is undesired.
CM_ScalarEpilogueNotNeededUsePredicate
CM_ScalarEpilogueNotNeededUsePredicate,
// Directive indicating we must either tail fold or not vectorize
CM_ScalarEpilogueNotAllowedUsePredicate
};
/// LoopVectorizationCostModel - estimates the expected speedups due to
@ -5463,6 +5466,8 @@ LoopVectorizationCostModel::computeMaxVF(ElementCount UserVF, unsigned UserIC) {
switch (ScalarEpilogueStatus) {
case CM_ScalarEpilogueAllowed:
return MaxVF;
case CM_ScalarEpilogueNotAllowedUsePredicate:
LLVM_FALLTHROUGH;
case CM_ScalarEpilogueNotNeededUsePredicate:
LLVM_DEBUG(
dbgs() << "LV: vector predicate hint/switch found.\n"
@ -5522,16 +5527,17 @@ LoopVectorizationCostModel::computeMaxVF(ElementCount UserVF, unsigned UserIC) {
// If there was a tail-folding hint/switch, but we can't fold the tail by
// masking, fallback to a vectorization with a scalar epilogue.
if (ScalarEpilogueStatus == CM_ScalarEpilogueNotNeededUsePredicate) {
if (PreferPredicateOverEpilogue == PreferPredicateTy::PredicateOrDontVectorize) {
LLVM_DEBUG(dbgs() << "LV: Can't fold tail by masking: don't vectorize\n");
return None;
}
LLVM_DEBUG(dbgs() << "LV: Cannot fold tail by masking: vectorize with a "
"scalar epilogue instead.\n");
ScalarEpilogueStatus = CM_ScalarEpilogueAllowed;
return MaxVF;
}
if (ScalarEpilogueStatus == CM_ScalarEpilogueNotAllowedUsePredicate) {
LLVM_DEBUG(dbgs() << "LV: Can't fold tail by masking: don't vectorize\n");
return None;
}
if (TC == 0) {
reportVectorizationFailure(
"Unable to calculate the loop count due to complex control flow",
@ -8855,22 +8861,29 @@ static ScalarEpilogueLowering getScalarEpilogueLowering(
Hints.getForce() != LoopVectorizeHints::FK_Enabled))
return CM_ScalarEpilogueNotAllowedOptSize;
bool PredicateOptDisabled = PreferPredicateOverEpilogue.getNumOccurrences() &&
!PreferPredicateOverEpilogue;
// 2) If set, obey the directives
if (PreferPredicateOverEpilogue.getNumOccurrences()) {
switch (PreferPredicateOverEpilogue) {
case PreferPredicateTy::ScalarEpilogue:
return CM_ScalarEpilogueAllowed;
case PreferPredicateTy::PredicateElseScalarEpilogue:
return CM_ScalarEpilogueNotNeededUsePredicate;
case PreferPredicateTy::PredicateOrDontVectorize:
return CM_ScalarEpilogueNotAllowedUsePredicate;
};
}
// 2) Next, if disabling predication is requested on the command line, honour
// this and request a scalar epilogue.
if (PredicateOptDisabled)
// 3) If set, obey the hints
switch (Hints.getPredicate()) {
case LoopVectorizeHints::FK_Enabled:
return CM_ScalarEpilogueNotNeededUsePredicate;
case LoopVectorizeHints::FK_Disabled:
return CM_ScalarEpilogueAllowed;
};
// 3) and 4) look if enabling predication is requested on the command line,
// with a loop hint, or if the TTI hook indicates this is profitable, request
// predication.
if (PreferPredicateOverEpilogue ||
Hints.getPredicate() == LoopVectorizeHints::FK_Enabled ||
(TTI->preferPredicateOverEpilogue(L, LI, *SE, *AC, TLI, DT,
LVL.getLAI()) &&
Hints.getPredicate() != LoopVectorizeHints::FK_Disabled))
// 4) if the TTI hook indicates this is profitable, request predication.
if (TTI->preferPredicateOverEpilogue(L, LI, *SE, *AC, TLI, DT,
LVL.getLAI()))
return CM_ScalarEpilogueNotNeededUsePredicate;
return CM_ScalarEpilogueAllowed;