[Mesa-dev] [PATCH 07/38] i965/vec4: Take into account all instruction fields in CSE instructions_match().

[Francisco Jerez]

Matt Turner <mattst88 at gmail.com> writes:

> On Thu, Jun 4, 2015 at 9:04 AM, Francisco Jerez <currojerez at riseup.net> wrote:
>> Most of these fields affect the behaviour of the instruction so it
>> could actually break the program if we CSE a pair of otherwise
>> matching instructions with different values of these fields.
>> ---
>>  src/mesa/drivers/dri/i965/brw_vec4_cse.cpp | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp b/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
>> index 9147c3c..c9fe0ce 100644
>> --- a/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_vec4_cse.cpp
>> @@ -114,8 +114,16 @@ instructions_match(vec4_instruction *a, vec4_instruction *b)
>>  {
>>     return a->opcode == b->opcode &&
>>            a->saturate == b->saturate &&
>> +          a->predicate == b->predicate &&
>> +          a->predicate_inverse == b->predicate_inverse &&
>>            a->conditional_mod == b->conditional_mod &&
>> +          a->flag_subreg == b->flag_subreg &&
>>            a->dst.type == b->dst.type &&
>> +          a->offset == b->offset &&
>> +          a->mlen == b->mlen &&
>> +          a->base_mrf == b->base_mrf &&
>> +          a->header_size == b->header_size &&
>> +          a->shadow_compare == b->shadow_compare &&
>
> I guess this is fine, but it's really just dead code. We don't CSE
> textures in the vec4 backend.

We don't today, but we're not that far from supporting send-from-GRF
texturing and some load-payload-like instruction in the vec4 back-end,
and when we do, it seems like a nice trap for the future to have a
function called "instructions_match()" that only checks if half of the
instruction matches...

That said, I should probably have made it more clear in the commit
message that this doesn't fix any bug that I'm aware of -- I mostly
copy-pasted the commit message from the commit that does the same in the
FS back-end, which fixes an actual bug.
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