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InstCombine: Fix assert when reassociating fsub with undef 

There is logic to track the expected number of instructions
produced. It thought in this case an instruction would
be necessary to negate the result, but here it folded
into a ConstantExpr fneg when the non-undef value operand
was cancelled out by the second fsub.

I'm not sure why we don't fold constant FP ops with undef currently,
but I think that would also avoid this problem.

llvm-svn: 301199
This commit is contained in:
Matt Arsenault 2017-04-24 17:24:37 +00:00
parent 8b37326ae2
commit 02907f3039
2 changed files with 49 additions and 0 deletions
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5
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -794,6 +794,11 @@ unsigned FAddCombine::calcInstrNumber(const AddendVect &Opnds) {
if (Opnd->isConstant())
continue;
// The constant check above is really for a few special constant
// coefficients.
if (isa<UndefValue>(Opnd->getSymVal()))
continue;
const FAddendCoef &CE = Opnd->getCoef();
if (CE.isMinusOne() || CE.isMinusTwo())
NegOpndNum++;

44
llvm/test/Transforms/InstCombine/fsub.ll
View File

@ -21,3 +21,47 @@ define double @test2(double %x, double %y) nounwind {
ret double %t2
}
; CHECK-LABEL: @fsub_undef(
; CHECK: %sub = fsub float %val, undef
define float @fsub_undef(float %val) {
bb:
%sub = fsub float %val, undef
ret float %sub
}
; XXX - Why doesn't this fold to undef?
; CHECK-LABEL: @fsub_fast_undef(
; CHCK: %sub = fsub fast float %val, undef
define float @fsub_fast_undef(float %val) {
bb:
%sub = fsub fast float %val, undef
ret float %sub
}
; CHECK-LABEL: @fneg_undef(
; CHECK: ret float fsub (float -0.000000e+00, float undef)
define float @fneg_undef(float %val) {
bb:
%sub = fsub float -0.0, undef
ret float %sub
}
; CHECK-LABEL: @fneg_fast_undef(
; CHECK: ret float fsub (float -0.000000e+00, float undef)
define float @fneg_fast_undef(float %val) {
bb:
%sub = fsub fast float -0.0, undef
ret float %sub
}
; This folds to a constant expression, which produced 0 instructions
; contrary to the expected one for negation.
; CHECK-LABEL: @inconsistent_numbers_fsub_undef(
; CHECK: ret float fsub (float -0.000000e+00, float undef)
define float @inconsistent_numbers_fsub_undef(float %val) {
bb:
%sub0 = fsub fast float %val, undef
%sub1 = fsub fast float %sub0, %val
ret float %sub1
}