[Mesa-dev] [PATCH] i965: Avoid dependency hints on math opcodes

[Jordan Justen]

On Wed, Feb 12, 2014 at 9:25 PM, Ian Romanick <idr at freedesktop.org> wrote:
> On 02/12/2014 06:59 PM, Matt Turner wrote:
>> On Wed, Feb 12, 2014 at 4:24 PM,  <mike at lunarg.com> wrote:
>>> From: Mike Stroyan <mike at LunarG.com>
>>>
>>>   Putting NoDDClr and NoDDChk dependency control on instruction
>>> sequences that include math opcodes can cause corruption of channels.
>>> Treat math opcodes like send opcodes and suppress dependency hinting.
>>>
>>> Signed-off-by: Mike Stroyan <mike at LunarG.com>
>>> Tested-by: Tony Bertapelli <anthony.p.bertapelli at intel.com>
>>> ---
>>>  src/mesa/drivers/dri/i965/brw_vec4.cpp | 8 ++++++++
>>>  1 file changed, 8 insertions(+)
>>>
>>> diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
>>> index dd23ed4..1c42ca8 100644
>>> --- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
>>> +++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
>>> @@ -717,6 +717,14 @@ vec4_visitor::opt_set_dependency_control()
>>>              continue;
>>>           }
>>>
>>> +         /* Dependency control does not work well over math instructions.
>>> +          */
>>> +         if (inst->is_math()) {
>>> +            memset(last_grf_write, 0, sizeof(last_grf_write));
>>> +            memset(last_mrf_write, 0, sizeof(last_mrf_write));
>>> +            continue;
>>> +         }
>>> +
>>>           /* Now, see if we can do dependency control for this instruction
>>>            * against a previous one writing to its destination.
>>>            */
>>> --
>>> 1.8.3.2
>>
>> I can't find any mention of this in the PRMs. Do we have a bug report
>> or something that this fixes?
>
> We have some code involving a lot of inversesqrt calls that I haven't
> quite turned into a shader_runner test yet... I also wonder if this
> could be related to the Dota2 too-much-specular bug, but I haven't tried
> that out yet either.

It didn't seem to help this bug:
https://bugs.freedesktop.org/show_bug.cgi?id=74700

-Jordan