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[InstCombine] Remove dead poison check. NFCI #141264

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Merged
merged 1 commit into from
May 23, 2025
Merged

[InstCombine] Remove dead poison check. NFCI #141264

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19 changes: 0 additions & 19 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2254,25 +2254,6 @@ Instruction *InstCombinerImpl::foldVectorBinop(BinaryOperator &Inst) {
}
NewVecC[ShMask[I]] = CElt;
}
// If this is a widening shuffle, we must be able to extend with poison
// elements. If the original binop does not produce a poison in the high
// lanes, then this transform is not safe.
// Similarly for poison lanes due to the shuffle mask, we can only
// transform binops that preserve poison.
// TODO: We could shuffle those non-poison constant values into the
// result by using a constant vector (rather than an poison vector)
// as operand 1 of the new binop, but that might be too aggressive
// for target-independent shuffle creation.
if (I >= SrcVecNumElts || ShMask[I] < 0) {
Constant *MaybePoison =
ConstOp1
? ConstantFoldBinaryOpOperands(Opcode, PoisonScalar, CElt, DL)
: ConstantFoldBinaryOpOperands(Opcode, CElt, PoisonScalar, DL);
if (!MaybePoison || !isa<PoisonValue>(MaybePoison)) {
MayChange = false;
break;
}
}
}
if (MayChange) {
Constant *NewC = ConstantVector::get(NewVecC);
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7 changes: 5 additions & 2 deletions llvm/test/Transforms/InstCombine/vec_shuffle.ll
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Expand Up @@ -732,8 +732,11 @@ define <4 x i16> @widening_shuffle_shl_constant_op1_non0(<2 x i16> %v) {
ret <4 x i16> %bo
}

; A binop that does not produce undef in the high lanes can not be moved before the shuffle.
; This is not ok because 'or -1, undef --> -1' but moving the shuffle results in undef instead.
; Previously, a shufflevector would produce an undef element from an undef mask
; index, which meant that pulling the shuffle out wasn't correct if the original
; binary op produced a non-undef result, e.g. or -1, undef --> -1.
;
; However nowadays shufflevector produces poison, which is safe to propagate.

define <4 x i16> @widening_shuffle_or(<2 x i16> %v) {
; CHECK-LABEL: @widening_shuffle_or(
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