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QingShan Zhangtstellar
QingShan Zhang
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[DAGCombine] Check the uses of negated floating constant and remove the hack
PowerPC hits an assertion due to somewhat the same reason as https://reviews.llvm.org/D70975. Though there are already some hack, it still failed with some case, when the operand 0 is NOT a const fp, it is another fma that with const fp. And that const fp is negated which result in multi-uses. A better fix is to check the uses of the negated const fp. If there are already use of its negated value, we will have benefit as no extra Node is added. Differential revision: https://reviews.llvm.org/D75501 (cherry picked from commit 3906ae3)
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Diff for: ‎llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

+15-11
Original file line numberDiff line numberDiff line change
@@ -5490,9 +5490,20 @@ char TargetLowering::isNegatibleForFree(SDValue Op, SelectionDAG &DAG,
54905490
EVT VT = Op.getValueType();
54915491
const SDNodeFlags Flags = Op->getFlags();
54925492
const TargetOptions &Options = DAG.getTarget().Options;
5493-
if (!Op.hasOneUse() && !(Op.getOpcode() == ISD::FP_EXTEND &&
5494-
isFPExtFree(VT, Op.getOperand(0).getValueType())))
5495-
return 0;
5493+
if (!Op.hasOneUse()) {
5494+
bool IsFreeExtend = Op.getOpcode() == ISD::FP_EXTEND &&
5495+
isFPExtFree(VT, Op.getOperand(0).getValueType());
5496+
5497+
// If we already have the use of the negated floating constant, it is free
5498+
// to negate it even it has multiple uses.
5499+
bool IsFreeConstant =
5500+
Op.getOpcode() == ISD::ConstantFP &&
5501+
!getNegatedExpression(Op, DAG, LegalOperations, ForCodeSize)
5502+
.use_empty();
5503+
5504+
if (!IsFreeExtend && !IsFreeConstant)
5505+
return 0;
5506+
}
54965507

54975508
// Don't recurse exponentially.
54985509
if (Depth > SelectionDAG::MaxRecursionDepth)
@@ -5687,14 +5698,7 @@ SDValue TargetLowering::getNegatedExpression(SDValue Op, SelectionDAG &DAG,
56875698
ForCodeSize, Depth + 1);
56885699
char V1 = isNegatibleForFree(Op.getOperand(1), DAG, LegalOperations,
56895700
ForCodeSize, Depth + 1);
5690-
// TODO: This is a hack. It is possible that costs have changed between now
5691-
// and the initial calls to isNegatibleForFree(). That is because we
5692-
// are rewriting the expression, and that may change the number of
5693-
// uses (and therefore the cost) of values. If the negation costs are
5694-
// equal, only negate this value if it is a constant. Otherwise, try
5695-
// operand 1. A better fix would eliminate uses as a cost factor or
5696-
// track the change in uses as we rewrite the expression.
5697-
if (V0 > V1 || (V0 == V1 && isa<ConstantFPSDNode>(Op.getOperand(0)))) {
5701+
if (V0 > V1) {
56985702
// fold (fneg (fma X, Y, Z)) -> (fma (fneg X), Y, (fneg Z))
56995703
SDValue Neg0 = getNegatedExpression(
57005704
Op.getOperand(0), DAG, LegalOperations, ForCodeSize, Depth + 1);

Diff for: ‎llvm/test/CodeGen/PowerPC/fma-combine.ll

+101
Original file line numberDiff line numberDiff line change
@@ -137,3 +137,104 @@ entry:
137137
%add = fsub double %mul, %a
138138
ret double %add
139139
}
140+
141+
define float @fma_combine_no_ice() {
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; CHECK-FAST-LABEL: fma_combine_no_ice:
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; CHECK-FAST: # %bb.0:
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; CHECK-FAST-NEXT: addis 3, 2, .LCPI4_0@toc@ha
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; CHECK-FAST-NEXT: addis 4, 2, .LCPI4_1@toc@ha
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; CHECK-FAST-NEXT: lfs 0, .LCPI4_0@toc@l(3)
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; CHECK-FAST-NEXT: lfsx 2, 0, 3
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; CHECK-FAST-NEXT: addis 3, 2, .LCPI4_2@toc@ha
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; CHECK-FAST-NEXT: lfs 3, .LCPI4_1@toc@l(4)
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; CHECK-FAST-NEXT: lfs 1, .LCPI4_2@toc@l(3)
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; CHECK-FAST-NEXT: xsmaddasp 3, 2, 0
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; CHECK-FAST-NEXT: xsmaddasp 1, 2, 3
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; CHECK-FAST-NEXT: xsnmsubasp 1, 3, 2
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; CHECK-FAST-NEXT: blr
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;
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; CHECK-FAST-NOVSX-LABEL: fma_combine_no_ice:
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; CHECK-FAST-NOVSX: # %bb.0:
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; CHECK-FAST-NOVSX-NEXT: addis 3, 2, .LCPI4_0@toc@ha
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; CHECK-FAST-NOVSX-NEXT: lfs 0, .LCPI4_0@toc@l(3)
160+
; CHECK-FAST-NOVSX-NEXT: addis 3, 2, .LCPI4_1@toc@ha
161+
; CHECK-FAST-NOVSX-NEXT: lfs 1, 0(3)
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; CHECK-FAST-NOVSX-NEXT: lfs 2, .LCPI4_1@toc@l(3)
163+
; CHECK-FAST-NOVSX-NEXT: addis 3, 2, .LCPI4_2@toc@ha
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; CHECK-FAST-NOVSX-NEXT: fmadds 0, 1, 2, 0
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; CHECK-FAST-NOVSX-NEXT: lfs 2, .LCPI4_2@toc@l(3)
166+
; CHECK-FAST-NOVSX-NEXT: fmadds 2, 1, 0, 2
167+
; CHECK-FAST-NOVSX-NEXT: fnmsubs 1, 0, 1, 2
168+
; CHECK-FAST-NOVSX-NEXT: blr
169+
;
170+
; CHECK-LABEL: fma_combine_no_ice:
171+
; CHECK: # %bb.0:
172+
; CHECK-NEXT: addis 3, 2, .LCPI4_0@toc@ha
173+
; CHECK-NEXT: addis 4, 2, .LCPI4_1@toc@ha
174+
; CHECK-NEXT: lfs 0, .LCPI4_0@toc@l(3)
175+
; CHECK-NEXT: lfsx 2, 0, 3
176+
; CHECK-NEXT: addis 3, 2, .LCPI4_2@toc@ha
177+
; CHECK-NEXT: lfs 3, .LCPI4_1@toc@l(4)
178+
; CHECK-NEXT: lfs 1, .LCPI4_2@toc@l(3)
179+
; CHECK-NEXT: xsmaddasp 3, 2, 0
180+
; CHECK-NEXT: xsmaddasp 1, 2, 3
181+
; CHECK-NEXT: xsnmsubasp 1, 3, 2
182+
; CHECK-NEXT: blr
183+
%tmp = load float, float* undef, align 4
184+
%tmp2 = load float, float* undef, align 4
185+
%tmp3 = fmul fast float %tmp, 0x3FE372D780000000
186+
%tmp4 = fadd fast float %tmp3, 1.000000e+00
187+
%tmp5 = fmul fast float %tmp2, %tmp4
188+
%tmp6 = load float, float* undef, align 4
189+
%tmp7 = load float, float* undef, align 4
190+
%tmp8 = fmul fast float %tmp7, 0x3FE372D780000000
191+
%tmp9 = fsub fast float -1.000000e+00, %tmp8
192+
%tmp10 = fmul fast float %tmp9, %tmp6
193+
%tmp11 = fadd fast float %tmp5, 5.000000e-01
194+
%tmp12 = fadd fast float %tmp11, %tmp10
195+
ret float %tmp12
196+
}
197+
198+
; This would crash while trying getNegatedExpression().
199+
define double @getNegatedExpression_crash(double %x, double %y) {
200+
; CHECK-FAST-LABEL: getNegatedExpression_crash:
201+
; CHECK-FAST: # %bb.0:
202+
; CHECK-FAST-NEXT: addis 3, 2, .LCPI5_1@toc@ha
203+
; CHECK-FAST-NEXT: addis 4, 2, .LCPI5_0@toc@ha
204+
; CHECK-FAST-NEXT: lfs 3, .LCPI5_1@toc@l(3)
205+
; CHECK-FAST-NEXT: lfs 4, .LCPI5_0@toc@l(4)
206+
; CHECK-FAST-NEXT: xssubdp 0, 1, 3
207+
; CHECK-FAST-NEXT: xsmaddadp 3, 1, 4
208+
; CHECK-FAST-NEXT: xsmaddadp 0, 3, 2
209+
; CHECK-FAST-NEXT: fmr 1, 0
210+
; CHECK-FAST-NEXT: blr
211+
;
212+
; CHECK-FAST-NOVSX-LABEL: getNegatedExpression_crash:
213+
; CHECK-FAST-NOVSX: # %bb.0:
214+
; CHECK-FAST-NOVSX-NEXT: addis 3, 2, .LCPI5_0@toc@ha
215+
; CHECK-FAST-NOVSX-NEXT: addis 4, 2, .LCPI5_1@toc@ha
216+
; CHECK-FAST-NOVSX-NEXT: lfs 0, .LCPI5_0@toc@l(3)
217+
; CHECK-FAST-NOVSX-NEXT: lfs 3, .LCPI5_1@toc@l(4)
218+
; CHECK-FAST-NOVSX-NEXT: fmadd 3, 1, 3, 0
219+
; CHECK-FAST-NOVSX-NEXT: fsub 0, 1, 0
220+
; CHECK-FAST-NOVSX-NEXT: fmadd 1, 3, 2, 0
221+
; CHECK-FAST-NOVSX-NEXT: blr
222+
;
223+
; CHECK-LABEL: getNegatedExpression_crash:
224+
; CHECK: # %bb.0:
225+
; CHECK-NEXT: addis 3, 2, .LCPI5_1@toc@ha
226+
; CHECK-NEXT: addis 4, 2, .LCPI5_0@toc@ha
227+
; CHECK-NEXT: lfs 3, .LCPI5_1@toc@l(3)
228+
; CHECK-NEXT: lfs 4, .LCPI5_0@toc@l(4)
229+
; CHECK-NEXT: xssubdp 0, 1, 3
230+
; CHECK-NEXT: xsmaddadp 3, 1, 4
231+
; CHECK-NEXT: xsmaddadp 0, 3, 2
232+
; CHECK-NEXT: fmr 1, 0
233+
; CHECK-NEXT: blr
234+
%neg = fneg fast double %x
235+
%fma = call fast double @llvm.fma.f64(double %neg, double 42.0, double -1.0)
236+
%add = fadd fast double %x, 1.0
237+
%fma1 = call fast double @llvm.fma.f64(double %fma, double %y, double %add)
238+
ret double %fma1
239+
}
240+
declare double @llvm.fma.f64(double, double, double) nounwind readnone

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