[Mesa-dev] [PATCH 03/10] i965/fs: Add vector float immediate infrastructure.

[Matt Turner]

On Fri, Oct 24, 2014 at 1:34 AM, Francisco Jerez <currojerez at riseup.net> wrote:
> Matt Turner <mattst88 at gmail.com> writes:
>
>> ---
>>  src/mesa/drivers/dri/i965/brw_fs.cpp           | 20 ++++++++++++++++++++
>>  src/mesa/drivers/dri/i965/brw_fs.h             |  1 +
>>  src/mesa/drivers/dri/i965/brw_fs_generator.cpp |  3 +++
>>  3 files changed, 24 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs.cpp b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> index 983e8db..ffe0a5b 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs.cpp
>> @@ -44,6 +44,7 @@ extern "C" {
>>  #include "brw_context.h"
>>  #include "brw_eu.h"
>>  #include "brw_wm.h"
>> +#include "brw_packed_float.h"
>>  }
>>  #include "brw_fs.h"
>>  #include "brw_cfg.h"
>> @@ -581,6 +582,18 @@ fs_reg::fs_reg(uint32_t u)
>>     this->width = 1;
>>  }
>>
>> +/** Vector float immediate value constructor. */
>> +fs_reg::fs_reg(uint8_t vf[4])
>> +{
>> +   init();
>> +   this->file = IMM;
>> +   this->type = BRW_REGISTER_TYPE_VF;
>> +   this->fixed_hw_reg.dw1.ud = (vf[0] <<  0) |
>> +                               (vf[1] <<  8) |
>> +                               (vf[2] << 16) |
>> +                               (vf[3] << 24);
>> +}
>> +
>
> IMHO it would be a lot more convenient to have this function take four
> float arguments and carry out the conversion to 8-bit here.  I suspect
> that in most cases the arguments of this constructor (and the same goes
> for src_reg) will be known at compile time so we could just add an
> assertion to check that the conversion was carried out exactly.

That would work if we're constructing VF immediates from known good
values, but in cases like in an optimization, you're always going to
have to check whether the values are representable in VF. If they're
not, the pass will have to fail.

In that case, you've already done the conversion. See this pass, for example:

http://cgit.freedesktop.org/~mattst88/mesa/commit/?h=line&id=dd9504e28037aee5ade38bb8b8d51bd39a444e12