Re: [PATCH 0/1] target/arm: Check NaN mode before silencing NaN

[Peter Maydell]

On Mon, 28 Jun 2021 at 16:05, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> On 6/28/21 7:54 AM, Peter Maydell wrote:
> > Richard, Alex: what is the assertion trying to achieve ? It doesn't
> > seem entirely obvious to me that because we're in default-NaN mode
> > (which is a property of the *output* of FPU insns) that we should
> > blow up on calling float*_silence_nan() (which is typically an action
> > performed on the *input* of FPU insns).
>
> This was in response to e9e5534ff30.
>
> My assumption in adding the assert is that it was probably a configuration 
> error.  If you
> disagree, I suppose we can revert it, as it's not critical.
>
> > If we do want to keep the assertion, somebody should audit the
> > other frontends that use float*_silence_nan() (i386, m68k, s390x)
> > to see if they also need updating.
>
> Easily done.  None of them ever set default_nan mode.

Hmm, I guess this was just Arm, then, and the current code
is silencing the NaN and then ignoring that result in favour
of the default NaN, which is a bit unnecessary. Plus, we have
this patch now thanks to Joe and we don't have the hypothetical
"drop the assert" patch :-)

Applied to target-arm.next, thanks.

-- PMM