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[SCEV] Revert two speculative compile time optimizations which made no difference 

Revert "[SCEV] Defer all work from ea12c2cb as late as possible"
Revert "[SCEV] Defer loop property checks from ea12c2cb as late as possible"

This reverts commit 734abbad79 and  1a5666acb2.

Both of these changes were speculative attempts to address a compile time regression.  Neither worked, and both complicated the code in undesirable ways.
This commit is contained in:
Philip Reames 2021-11-19 08:40:24 -08:00
parent af57a71d18
commit 28000587e1
1 changed files with 10 additions and 18 deletions
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28
llvm/lib/Analysis/ScalarEvolution.cpp
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@ -8321,14 +8321,8 @@ ScalarEvolution::computeExitLimitFromICmp(const Loop *L,
// the same values on self-wrap of the IV, then we can infer that IV
// doesn't self wrap because if it did, we'd have an infinite (undefined)
// loop.
if (ControlsExit) {
auto deferredLoopProperties = [&]() {
// Conceptually, these two checks should be in the immediately guarding
// if clause, but we defer their actual execution to after the cheaper
// checks have all been done.
return isLoopInvariant(RHS, L) && loopHasNoAbnormalExits(L) &&
loopIsFiniteByAssumption(L);
};
if (ControlsExit && isLoopInvariant(RHS, L) && loopHasNoAbnormalExits(L) &&
loopIsFiniteByAssumption(L)) {
// TODO: We can peel off any functions which are invertible *in L*. Loop
// invariant terms are effectively constants for our purposes here.
@ -8336,16 +8330,14 @@ ScalarEvolution::computeExitLimitFromICmp(const Loop *L,
if (auto *ZExt = dyn_cast<SCEVZeroExtendExpr>(LHS))
InnerLHS = ZExt->getOperand();
if (const SCEVAddRecExpr *AR = dyn_cast<SCEVAddRecExpr>(InnerLHS)) {
if (!AR->hasNoSelfWrap() && AR->getLoop() == L && AR->isAffine()) {
auto *StrideC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this));
if (StrideC && StrideC->getAPInt().isPowerOf2() &&
deferredLoopProperties()) {
auto Flags = AR->getNoWrapFlags();
Flags = setFlags(Flags, SCEV::FlagNW);
SmallVector<const SCEV*> Operands{AR->operands()};
Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
}
auto *StrideC = dyn_cast<SCEVConstant>(AR->getStepRecurrence(*this));
if (!AR->hasNoSelfWrap() && AR->getLoop() == L && AR->isAffine() &&
StrideC && StrideC->getAPInt().isPowerOf2()) {
auto Flags = AR->getNoWrapFlags();
Flags = setFlags(Flags, SCEV::FlagNW);
SmallVector<const SCEV*> Operands{AR->operands()};
Flags = StrengthenNoWrapFlags(this, scAddRecExpr, Operands, Flags);
setNoWrapFlags(const_cast<SCEVAddRecExpr *>(AR), Flags);
}
}
}