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[DAG] SimplifyDemandedVectorElts - if every and/mul element-pair has a zero/undef then just constant fold to zero

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This commit is contained in:
Simon Pilgrim 2022-07-24 12:00:31 +01:00
parent 69d1e805ce
commit a3e38b4a20
2 changed files with 7 additions and 4 deletions
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7
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
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@ -3364,6 +3364,12 @@ bool TargetLowering::SimplifyDemandedVectorElts(
TLO, Depth + 1))
return true;
// If every element pair has a zero/undef then just fold to zero.
// fold (and x, undef) -> 0 / (and x, 0) -> 0
// fold (mul x, undef) -> 0 / (mul x, 0) -> 0
if (DemandedElts.isSubsetOf(SrcZero | KnownZero | SrcUndef | KnownUndef))
return TLO.CombineTo(Op, TLO.DAG.getConstant(0, SDLoc(Op), VT));
// If either side has a zero element, then the result element is zero, even
// if the other is an UNDEF.
// TODO: Extend getKnownUndefForVectorBinop to also deal with known zeros
@ -3373,7 +3379,6 @@ bool TargetLowering::SimplifyDemandedVectorElts(
KnownUndef &= ~KnownZero;
// Attempt to avoid multi-use ops if we don't need anything from them.
// TODO - use KnownUndef to relax the demandedelts?
if (!DemandedElts.isAllOnes())
if (SimplifyDemandedVectorEltsBinOp(Op0, Op1))
return true;

4
llvm/test/CodeGen/X86/vector-partial-undef.ll
View file

@ -85,9 +85,7 @@ define <4 x i64> @and_undef_elts(<2 x i64> %x) {
;
; AVX-LABEL: and_undef_elts:
; AVX: # %bb.0:
; AVX-NEXT: # kill: def $xmm0 killed $xmm0 def $ymm0
; AVX-NEXT: vpermpd {{.*#+}} ymm0 = ymm0[3,0,1,2]
; AVX-NEXT: vandps {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %ymm0, %ymm0
; AVX-NEXT: vxorps %xmm0, %xmm0, %xmm0
; AVX-NEXT: retq
%extend = shufflevector <2 x i64> %x, <2 x i64> undef, <4 x i32> <i32 0, i32 1, i32 undef, i32 undef>
%bogus_bo = and <4 x i64> %extend, <i64 undef, i64 undef, i64 42, i64 43>