[PATCH] D139455: AMDGPU: Document denormal behavior

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added a comment.

In D139455#3998100 <https://reviews.llvm.org/D139455#3998100>, @artem.tamazov wrote:

> In D139455#3996367 <https://reviews.llvm.org/D139455#3996367>, @arsenm wrote:
>
>> We have preserve-sign behavior and ignore positive-zero mode entirely. Also the modifiers are silently ignored for ieee mode =0. I don't remember what the wrong behavior depending on the denormal mode was, beyond don't use these without flushing
>
> I see. What I would like to emphasize is that the compiler should NOT use output modifiers for optimization when "denormal-fp-math"="preserve-sign" (in spite of modifiers will work in this mode), because output modifiers break sign preservation behavior. The compiler should use output modifiers only in "denormal-fp-math"="positive-zero" mode.

The whole point of this change is to document that the hardware has preserve sign denormal behavior and we do not support positive-zero mode. We only apply output modifiers with nsz and don't consider the denormal mode


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https://reviews.llvm.org/D139455