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[DAGCombiner] Fix PR25763 - vector comparison constant folding + sign-extension

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PR25763 demonstrated an issue with D14683 - vector comparison constant folding only works for i1 results, so we need to split off the sign-extension of the result to the required type. Luckily this can be done with the existing type legalization code.

llvm-svn: 255289
This commit is contained in:
Simon Pilgrim 2015-12-10 19:47:06 +00:00
parent f118529c0e
commit fcb5c2d030
2 changed files with 24 additions and 5 deletions
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13
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -3338,12 +3338,15 @@ SDValue SelectionDAG::FoldConstantVectorArithmetic(unsigned Opcode, SDLoc DL,
!std::all_of(Ops.begin(), Ops.end(), IsScalarOrSameVectorSize))
return SDValue();
// If we are comparing vectors, then the result needs to be a i1 boolean
// that is then sign-extended back to the legal result type.
EVT SVT = (Opcode == ISD::SETCC ? MVT::i1 : VT.getScalarType());
// Find legal integer scalar type for constant promotion and
// ensure that its scalar size is at least as large as source.
EVT SVT = VT.getScalarType();
EVT LegalSVT = SVT;
if (SVT.isInteger()) {
LegalSVT = TLI->getTypeToTransformTo(*getContext(), SVT);
EVT LegalSVT = VT.getScalarType();
if (LegalSVT.isInteger()) {
LegalSVT = TLI->getTypeToTransformTo(*getContext(), LegalSVT);
if (LegalSVT.bitsLT(SVT))
return SDValue();
}
@ -3380,7 +3383,7 @@ SDValue SelectionDAG::FoldConstantVectorArithmetic(unsigned Opcode, SDLoc DL,
// Legalize the (integer) scalar constant if necessary.
if (LegalSVT != SVT)
ScalarResult = getNode(ISD::ANY_EXTEND, DL, LegalSVT, ScalarResult);
ScalarResult = getNode(ISD::SIGN_EXTEND, DL, LegalSVT, ScalarResult);
// Scalar folding only succeeded if the result is a constant or UNDEF.
if (ScalarResult.getOpcode() != ISD::UNDEF &&

16
test/CodeGen/AArch64/fold-constants.ll
View File

@ -16,3 +16,19 @@ entry:
%vget_lane = extractelement <1 x i64> %4, i32 0
ret i64 %vget_lane
}
; PR25763 - folding constant vector comparisons with sign-extended result
define <8 x i16> @dotests_458() {
; CHECK-LABEL: dotests_458
; CHECK: movi d0, #0x00000000ff0000
; CHECK-NEXT: sshll v0.8h, v0.8b, #0
; CHECK-NEXT: ret
entry:
%vclz_v.i = call <8 x i8> @llvm.ctlz.v8i8(<8 x i8> <i8 127, i8 38, i8 -1, i8 -128, i8 127, i8 0, i8 0, i8 0>, i1 false) #6
%vsra_n = lshr <8 x i8> %vclz_v.i, <i8 5, i8 5, i8 5, i8 5, i8 5, i8 5, i8 5, i8 5>
%name_6 = or <8 x i8> %vsra_n, <i8 127, i8 -128, i8 -1, i8 67, i8 84, i8 127, i8 -1, i8 0>
%cmp.i603 = icmp slt <8 x i8> %name_6, <i8 -57, i8 -128, i8 127, i8 -128, i8 -1, i8 0, i8 -1, i8 -1>
%vmovl.i4.i = sext <8 x i1> %cmp.i603 to <8 x i16>
ret <8 x i16> %vmovl.i4.i
}
declare <8 x i8> @llvm.ctlz.v8i8(<8 x i8>, i1)