[PATCH] D70975: [SDAG] remove use restriction in isNegatibleForFree() when called from getNegatedExpression()

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.

In D70975#1780401 <https://reviews.llvm.org/D70975#1780401>, @fhahn wrote:

> In D70975#1780280 <https://reviews.llvm.org/D70975#1780280>, @spatel wrote:
>
> > In D70975#1780237 <https://reviews.llvm.org/D70975#1780237>, @fhahn wrote:
> >
> > > This seems to cause a DAGCombiner to not terminate for some inputs on AArch64. Unfortunately I cannot share the inputs that cause the cycle :(
> >
> >
> > Thanks for letting us know. Can you check if D70595 <https://reviews.llvm.org/D70595> would cause the same cycle?
> >  Will it be possible to reduce a test that can be shared? I'm not sure how to proceed without a test.
>
>
> I'll see if I can reduce it tomorrow! I looked at the debug output and it seems the cycle is quite simple.


With this patch, running `llc` on the snippet below causes a combiner cycle.

  define linkonce_odr i64 @quux(double* %arg, double %arg1, double %arg2, double %arg3, double %arg4, double %arg5) {
  bb:
    %tmp = fdiv double 1.000000e+00, %arg1
    %tmp6 = fmul double %tmp, %arg2
    %tmp7 = fmul double %tmp, %arg3
    %tmp8 = fmul double %tmp, %arg4
    %tmp9 = fmul double %tmp, %arg5
    %tmp10 = fneg double %tmp7
    %tmp11 = fmul double %tmp6, %tmp8
    %tmp12 = fmul double %tmp9, 4.000000e+00
    %tmp13 = fsub double %tmp11, %tmp12
    %tmp14 = fneg double %tmp9
    %tmp15 = fmul double %tmp6, %tmp14
    %tmp16 = fmul double %tmp6, %tmp15
    %tmp17 = fmul double %tmp7, %tmp12
    %tmp18 = fadd double %tmp16, %tmp17
    %tmp19 = fmul double %tmp8, %tmp8
    %tmp20 = fsub double %tmp18, %tmp19
    %tmp21 = call i64 @wombat(double* nonnull undef, double 1.000000e+00, double %tmp10, double %tmp13, double %tmp20)
    ret i64 %tmp21
  }
  declare i64 @wombat(double*, double, double, double, double)


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https://reviews.llvm.org/D70975