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[SCEV] Match both (-1)b + a and a + (-1)b as a - b #84247

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Merged
merged 1 commit into from
Mar 6, 2024
Merged

[SCEV] Match both (-1)b + a and a + (-1)b as a - b #84247

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32 changes: 21 additions & 11 deletions llvm/lib/Analysis/ScalarEvolution.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -10577,6 +10577,25 @@ static bool HasSameValue(const SCEV *A, const SCEV *B) {
return false;
}

static bool MatchBinarySub(const SCEV *S, const SCEV *&LHS, const SCEV *&RHS) {
const SCEVAddExpr *Add = dyn_cast<SCEVAddExpr>(S);
if (!Add || Add->getNumOperands() != 2)
return false;
if (auto *ME = dyn_cast<SCEVMulExpr>(Add->getOperand(0));
ME && ME->getNumOperands() == 2 && ME->getOperand(0)->isAllOnesValue()) {
LHS = Add->getOperand(1);
RHS = ME->getOperand(1);
return true;
}
if (auto *ME = dyn_cast<SCEVMulExpr>(Add->getOperand(1));
ME && ME->getNumOperands() == 2 && ME->getOperand(0)->isAllOnesValue()) {
LHS = Add->getOperand(0);
RHS = ME->getOperand(1);
return true;
}
return false;
}

bool ScalarEvolution::SimplifyICmpOperands(ICmpInst::Predicate &Pred,
const SCEV *&LHS, const SCEV *&RHS,
unsigned Depth) {
Expand Down Expand Up @@ -10652,19 +10671,10 @@ bool ScalarEvolution::SimplifyICmpOperands(ICmpInst::Predicate &Pred,
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE:
// Fold ((-1) * %a) + %b == 0 (equivalent to %b-%a == 0) into %a == %b.
if (!RA)
if (const SCEVAddExpr *AE = dyn_cast<SCEVAddExpr>(LHS))
if (const SCEVMulExpr *ME =
dyn_cast<SCEVMulExpr>(AE->getOperand(0)))
if (AE->getNumOperands() == 2 && ME->getNumOperands() == 2 &&
ME->getOperand(0)->isAllOnesValue()) {
RHS = AE->getOperand(1);
LHS = ME->getOperand(1);
Changed = true;
}
if (RA.isZero() && MatchBinarySub(LHS, LHS, RHS))
Changed = true;
break;


// The "Should have been caught earlier!" messages refer to the fact
// that the ExactCR.isFullSet() or ExactCR.isEmptySet() check above
// should have fired on the corresponding cases, and canonicalized the
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Analysis/ScalarEvolution/trip-count.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -145,7 +145,7 @@ define void @dual_sext_ne_with_slt_guard(i8 %s, i8 %n) {
; CHECK-LABEL: 'dual_sext_ne_with_slt_guard'
; CHECK-NEXT: Determining loop execution counts for: @dual_sext_ne_with_slt_guard
; CHECK-NEXT: Loop %for.body: backedge-taken count is (-1 + (sext i8 %n to i64) + (-1 * (sext i8 %s to i64))<nsw>)
; CHECK-NEXT: Loop %for.body: constant max backedge-taken count is i64 -1
; CHECK-NEXT: Loop %for.body: constant max backedge-taken count is i64 -2
; CHECK-NEXT: Loop %for.body: symbolic max backedge-taken count is (-1 + (sext i8 %n to i64) + (-1 * (sext i8 %s to i64))<nsw>)
; CHECK-NEXT: Loop %for.body: Trip multiple is 1
;
Expand Down