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[TargetLowering] fix SETCC SETLT folding with FP types 

The bug was introduced with:
https://reviews.llvm.org/rL294863

...and manifests as a selection failure in x86, but that's actually
another bug. This fix prevents wrong codegen with -0.0, but in the
more common case when we have NSZ and NNAN (-ffast-math), we should 
still be able to fold this setcc/compare.

llvm-svn: 294924
This commit is contained in:
Sanjay Patel 2017-02-12 23:07:52 +00:00
parent 31e1b8fe48
commit 0557a44287
2 changed files with 37 additions and 9 deletions
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22
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -751,25 +751,29 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
KnownOne &= KnownOne2;
KnownZero &= KnownZero2;
break;
case ISD::SETCC:
case ISD::SETCC: {
SDValue Op0 = Op.getOperand(0);
SDValue Op1 = Op.getOperand(1);
ISD::CondCode CC = cast<CondCodeSDNode>(Op.getOperand(2))->get();
// If (1) we only need the sign-bit, (2) the setcc operands are the same
// width as the setcc result, and (3) the result of a setcc conforms to 0 or
// -1, we may be able to bypass the setcc.
if (NewMask.isSignBit() &&
Op.getOperand(0).getScalarValueSizeInBits() == BitWidth &&
if (NewMask.isSignBit() && Op0.getScalarValueSizeInBits() == BitWidth &&
getBooleanContents(Op.getValueType()) ==
BooleanContent::ZeroOrNegativeOneBooleanContent) {
ISD::CondCode CC = cast<CondCodeSDNode>(Op.getOperand(2))->get();
// If we're testing if X < 0, then this compare isn't needed - just use X!
if (CC == ISD::SETLT &&
(isNullConstant(Op.getOperand(1)) ||
ISD::isBuildVectorAllZeros(Op.getOperand(1).getNode())))
return TLO.CombineTo(Op, Op.getOperand(0));
// If we're testing X < 0, then this compare isn't needed - just use X!
// FIXME: We're limiting to integer types here, but this should also work
// if we don't care about FP signed-zero. The use of SETLT with FP means
// that we don't care about NaNs.
if (CC == ISD::SETLT && Op1.getValueType().isInteger() &&
(isNullConstant(Op1) || ISD::isBuildVectorAllZeros(Op1.getNode())))
return TLO.CombineTo(Op, Op0);
// TODO: Should we check for other forms of sign-bit comparisons?
// Examples: X <= -1, X >= 0
}
break;
}
case ISD::SHL:
if (ConstantSDNode *SA = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
unsigned ShAmt = SA->getZExtValue();

24
llvm/test/CodeGen/X86/vselect-pcmp.ll
View File

@ -317,3 +317,27 @@ define <8 x double> @signbit_sel_v8f64(<8 x double> %x, <8 x double> %y, <8 x i6
ret <8 x double> %z
}
; If we have a floating-point compare:
; (1) Don't die.
; (2) FIXME: If we don't care about signed-zero (and NaN?), the compare should still get folded.
define <4 x float> @signbit_sel_v4f32_fcmp(<4 x float> %x, <4 x float> %y, <4 x float> %mask) #0 {
; AVX12F-LABEL: signbit_sel_v4f32_fcmp:
; AVX12F: # BB#0:
; AVX12F-NEXT: vxorps %xmm2, %xmm2, %xmm2
; AVX12F-NEXT: vcmpltps %xmm2, %xmm0, %xmm2
; AVX12F-NEXT: vblendvps %xmm2, %xmm0, %xmm1, %xmm0
; AVX12F-NEXT: retq
;
; AVX512VL-LABEL: signbit_sel_v4f32_fcmp:
; AVX512VL: # BB#0:
; AVX512VL-NEXT: vpxor %xmm2, %xmm2, %xmm2
; AVX512VL-NEXT: vcmpltps %xmm2, %xmm0, %k1
; AVX512VL-NEXT: vblendmps %xmm0, %xmm1, %xmm0 {%k1}
; AVX512VL-NEXT: retq
%cmp = fcmp olt <4 x float> %x, zeroinitializer
%sel = select <4 x i1> %cmp, <4 x float> %x, <4 x float> %y
ret <4 x float> %sel
}
attributes #0 = { "no-nans-fp-math"="true" }