On 03/12/2014 11:30 AM, Kenneth Graunke wrote:
> On 03/12/2014 02:51 AM, Ilia Mirkin wrote:
>> On Wed, Mar 12, 2014 at 4:28 AM, Kenneth Graunke <kenn...@whitecape.org>
>> wrote:
>>> Ideally, we'd like to never even attempt the SIMD16 compile if we could
>>> know ahead of time that it won't succeed---it's purely a waste of time.
>>> This is especially important for state-based recompiles, which happen at
>>> draw time.
>>>
>>> The fragment shader compiler has a number of checks like:
>>>
>>> if (dispatch_width == 16)
>>> fail("...some reason...");
>>>
>>> This patch introduces a new no16() function which replaces the above
>>> pattern. In the SIMD8 compile, it sets a "SIMD16 will never work" flag.
>>> Then, brw_wm_fs_emit can check that flag, skip the SIMD16 compile, and
>>> issue a helpful performance warning if INTEL_DEBUG=perf is set. (In
>>> SIMD16 mode, no16() calls fail(), for safety's sake.)
>>>
>>> The great part is that this is not a heuristic---if the flag is set, we
>>> know with 100% certainty that the SIMD16 compile would fail. (It might
>>> fail anyway if we run out of registers, but it's always worth trying.)
>>>
>>> Signed-off-by: Kenneth Graunke <kenn...@whitecape.org>
>>> ---
>>> src/mesa/drivers/dri/i965/brw_fs.cpp | 69
>>> +++++++++++++++++++++++-----
>>> src/mesa/drivers/dri/i965/brw_fs.h | 4 ++
>>> src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 44 +++++++++---------
>>> 3 files changed, 83 insertions(+), 34 deletions(-)
>>>
>>> I forgot to send this one out...it applies on top of the previous 7 patches.
>>>
>>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp
>>> b/src/mesa/drivers/dri/i965/brw_fs.cpp
>>> index 62848be..9ad80c5 100644
>>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>>> @@ -647,9 +647,8 @@ fs_visitor::emit_shader_time_write(enum
>>> shader_time_shader_type type,
>>> }
>>>
>>> void
>>> -fs_visitor::fail(const char *format, ...)
>>> +fs_visitor::vfail(const char *format, va_list va)
>>> {
>>> - va_list va;
>>> char *msg;
>>>
>>> if (failed)
>>> @@ -657,9 +656,7 @@ fs_visitor::fail(const char *format, ...)
>>>
>>> failed = true;
>>>
>>> - va_start(va, format);
>>> msg = ralloc_vasprintf(mem_ctx, format, va);
>>> - va_end(va);
>>> msg = ralloc_asprintf(mem_ctx, "FS compile failed: %s\n", msg);
>>>
>>> this->fail_msg = msg;
>>> @@ -669,6 +666,49 @@ fs_visitor::fail(const char *format, ...)
>>> }
>>> }
>>>
>>> +void
>>> +fs_visitor::fail(const char *format, ...)
>>> +{
>>> + va_list va;
>>> +
>>> + va_start(va, format);
>>> + vfail(format, va);
>>> + va_end(va);
>>> +}
>>> +
>>> +/**
>>> + * Mark this program as impossible to compile in SIMD16 mode.
>>> + *
>>> + * During the SIMD8 compile (which happens first), we can detect and flag
>>> + * things that are unsupported in SIMD16 mode, so the compiler can skip
>>> + * the SIMD16 compile altogether.
>>> + *
>>> + * During a SIMD16 compile (if one happens anyway), this just calls fail().
>>> + */
>>> +void
>>> +fs_visitor::no16(const char *format, ...)
>>> +{
>>> + va_list va;
>>> +
>>> + va_start(va, format);
>>> +
>>> + if (dispatch_width == 16) {
>>> + vfail(format, va);
>>
>> I think there's a va_end() missing in this path. Not sure what the
>> end-effect of that is, but I'm pretty sure that the recommendation is
>> to always end the list before returning.
>
> Good catch, thanks!
>
> For v2, I've changed the code to:
>
> void
> fs_visitor::no16(const char *format, ...)
> {
> va_list va;
>
> va_start(va, format);
>
> if (dispatch_width == 16) {
> vfail(format, va);
> } else {
> simd16_unsupported = true;
>
> if (INTEL_DEBUG & DEBUG_PERF) {
> if (no16_msg)
> ralloc_vasprintf_append(&no16_msg, format, va);
> else
> no16_msg = ralloc_vasprintf(mem_ctx, format, va);
> }
> }
>
> va_end(va);
> }
>
> which should also address Ian's concern. (I'm not sure whether it's
> necessary, but it's easy enough to do, so why not play it safe?)I can get behind that. :) > --Ken
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