[Bug 103544] Graphical glitches r600 in game this war of mine linux native

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103544

--- Comment #6 from Ilia Mirkin <imirkin at alum.mit.edu> ---
(In reply to Roland Scheidegger from comment #5)
> I've actually got that game myself here.
> So I did the bisect and the winner is:
> ce7a045feeef8cad155f1c9aa07f166e146e3d00 is the first bad commit
> commit ce7a045feeef8cad155f1c9aa07f166e146e3d00
> Author: Ilia Mirkin <imirkin at alum.mit.edu>
> Date:   Mon Jan 23 20:53:50 2017 -0500
> 
>     r600g: use ieee variants of multiplication instructions
>     
>     This matches the behavior of most other drivers, including nouveau,
>     radeonsi, and i965.
>     
>     Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
>     Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>
> 
> Looks like some numerical issue then, albeit I don't know if the game is at
> fault here.

Apologies for the trouble.

The main difference between IEEE and non-IEEE is whether 0 * infinity = 0 or
NaN. IEEE makes it mean NaN. DX9 behavior is 0. I added a flag to be used by
st/nine to enable the DX9 behavior optionally, but leave the IEEE behavior for
GLSL. (There was some additional desire to expose that in a GL ext for WINE to
use, but it got shot down pretty quickly.)

Perhaps there are other changes from using the IEEE instruction variants, e.g.
denorms, which would be undesirable. I was never too familiar with the R600
ISA.

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