[Mesa-dev] [PATCH 1/5/2] i965/fs: Bail out of opt_sampler_eot() if last instruction isn't EOT.

[Francisco Jerez]

Francisco Jerez <currojerez at riseup.net> writes:

> Matt Turner <mattst88 at gmail.com> writes:
>
>> ... instead of assert failing. Can only happen when the program has an
>> unconditional infinite loop.
>
> I'm curious how the framebuffer write gets eliminated, I don't think DCE
> is smart enough currently to find out that the FB write is unreachable?
>
Ah, I guess this is supposed to prevent a regression from 'i965/cfg:
Ignore non-CF instructions in unreachable blocks.' but is not currently
an issue?  Uhm...

>> ---
>> Sigh.
>>
>>  src/mesa/drivers/dri/i965/brw_fs.cpp | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> index d1ac80a..08e9b6c 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> @@ -2511,8 +2511,9 @@ fs_visitor::opt_sampler_eot()
>>     /* Look for a texturing instruction immediately before the final FB_WRITE. */
>>     bblock_t *block = cfg->blocks[cfg->num_blocks - 1];
>>     fs_inst *fb_write = (fs_inst *)block->end();
>> -   assert(fb_write->eot);
>> -   assert(fb_write->opcode == FS_OPCODE_FB_WRITE_LOGICAL);
>> +   if (unlikely(!fb_write->eot) ||
>> +       unlikely(fb_write->opcode != FS_OPCODE_FB_WRITE_LOGICAL))
>> +      return false;
>>  
>
> Maybe we want something in between the two?  Like:
>
> |   if (unlikely(fb_write->opcode != FS_OPCODE_FB_WRITE_LOGICAL))
> |      return false;
> |
> |   assert(fb_write->eot);
>
> My thinking is that *if* the final instruction of the shader is a
> framebuffer write it should have already been marked EOT during
> translation.
>
>>     /* There wasn't one; nothing to do. */
>>     if (unlikely(fb_write->prev->is_head_sentinel()))
>> -- 
>> 2.7.3
>>
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