[Mesa-dev] [PATCH 01/11] i965/vs: Add support for splitting virtual GRFs.

[Eric Anholt]

Kenneth Graunke <kenneth at whitecape.org> writes:

> On 10/04/2012 04:07 PM, Eric Anholt wrote:
>> This should improve our ability to register allocate without spilling.
>> Unfortuantely, due to the live variable analysis being ignorant of loops, we
>> still have register allocation failures on some programs.
>> ---
>>   src/mesa/drivers/dri/i965/brw_vec4.cpp      |   54 +++++++++++++++++++++++++++
>>   src/mesa/drivers/dri/i965/brw_vec4.h        |    1 +
>>   src/mesa/drivers/dri/i965/brw_vec4_emit.cpp |    1 +
>>   3 files changed, 56 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_vec4.cpp b/src/mesa/drivers/dri/i965/brw_vec4.cpp
>> index 2941729..fbd49ca 100644
>> --- a/src/mesa/drivers/dri/i965/brw_vec4.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_vec4.cpp
>> @@ -865,4 +865,58 @@ vec4_visitor::opt_compute_to_mrf()
>>      return progress;
>>   }
>>
>> +/**
>> + * Splits virtual GRFs requesting more than one contiguous physical register.
>> + *
>> + * Unlike in the FS visitor, we have no SEND messages that return more than 1
>> + * register.  We also don't do any array access in register space, which would
>> + * have required contiguous physical registers.
>> + */
>
> It would be nice to mention what the VS /does/ have that occupies VGRFs 
> of size > 1.  Structures and matrices?
>
> Otherwise, this looks good.
> Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>

New function comment:

/**
 * Splits virtual GRFs requesting more than one contiguous physical register.
 *
 * We initially create large virtual GRFs for temporary structures, arrays,
 * and matrices, so that the dereference visitor functions can add reg_offsets
 * to work their way down to the actual member being accessed.
 *
 * Unlike in the FS visitor, though, we have no SEND messages that return more
 * than 1 register.  We also don't do any array access in register space,
 * which would have required contiguous physical registers.  Thus, all those
 * large virtual GRFs can be split up into independent single-register virtual
 * GRFs, making allocation and optimization easier.
 */
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