[llvm-dev] [FPEnv] FNEG instruction

[Cameron McInally via llvm-dev]

On Tue, Oct 2, 2018 at 12:09 PM Kevin Neal <Kevin.Neal at sas.com> wrote:

> If we don’t have constrained intrinsics for some of the fp math
> instructions then aren’t we risking non-strict optimizations?
>

So far we've only added constrained FP intrinsics for operations that have
side effects (i.e. can trap).

The quiet-computational sign-bit operations are special. They never have
side effects (i.e. never trap). We have not been able to find a bad
transformation for those (i.e. a xform to a trapping operation) other than
the FNEG(X) --> FSUB(-0.0, X) transform.

If you can find a transform from one of the quiet-computational operations
to a trapping operation, then we should discuss that.
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