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?)
--Ken
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