[llvm] [InstCombine] Fold `(icmp eq/ne (xor x, y), C1)` even if multiuse (PR #87275)
Nikita Popov via llvm-commits
llvm-commits at lists.llvm.org
Tue Apr 9 23:44:51 PDT 2024
================
@@ -1285,21 +1285,47 @@ Instruction *InstCombinerImpl::foldSelectValueEquivalence(SelectInst &Sel,
Swapped = true;
}
- // In X == Y ? f(X) : Z, try to evaluate f(Y) and replace the operand.
- // Make sure Y cannot be undef though, as we might pick different values for
- // undef in the icmp and in f(Y). Additionally, take care to avoid replacing
- // X == Y ? X : Z with X == Y ? Y : Z, as that would lead to an infinite
- // replacement cycle.
Value *CmpLHS = Cmp.getOperand(0), *CmpRHS = Cmp.getOperand(1);
- if (TrueVal != CmpLHS &&
- isGuaranteedNotToBeUndefOrPoison(CmpRHS, SQ.AC, &Sel, &DT)) {
- if (Value *V = simplifyWithOpReplaced(TrueVal, CmpLHS, CmpRHS, SQ,
- /* AllowRefinement */ true))
- // Require either the replacement or the simplification result to be a
- // constant to avoid infinite loops.
- // FIXME: Make this check more precise.
- if (isa<Constant>(CmpRHS) || isa<Constant>(V))
+ auto ReplaceLHSOpWithRHSOp = [&](Value *OldOp,
+ Value *NewOp) -> Instruction * {
+ // In X == Y ? f(X) : Z, try to evaluate f(Y) and replace the operand.
+ // Take care to avoid replacing X == Y ? X : Z with X == Y ? Y : Z, as that
+ // would lead to an infinite replacement cycle.
+ // If we will be able to evaluate f(Y) to a constant, we can allow undef,
+ // otherwise Y cannot be undef as we might pick different values for undef
+ // in the icmp and in f(Y). Additionally
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nikic wrote:
Cut off sentence.
https://github.com/llvm/llvm-project/pull/87275
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