[Mesa-dev] [PATCH 2/2] i965/fs: Don't double-accept operands of logical and/or/xor operations.

[Kenneth Graunke]

On 09/23/2013 02:52 PM, Matt Turner wrote:
> On Mon, Sep 23, 2013 at 2:12 PM, Kenneth Graunke <kenneth at whitecape.org> wrote:
>> emit_bool_to_cond_code() takes separate paths for ir_expressions and.
> 
> Sentence ends unexpectedly?

Oops.  I meant to delete that.

>> If the argument to emit_bool_to_cond_code() is an ir_expression, we
>> loop over the operands, calling accept() on each of them, which
>> generates assembly code to compute that subexpression.  We then emit
>> one or two final instruction that perform the top-level operation on
>> those operands.
>>
>> If it's not an expression (say, a boolean-valued variable), we simply
>> call accept() on the whole value.
>>
>> In commit 80ecb8f1 (i965/fs: Avoid generating extra AND instructions on
>> bool logic ops), Eric made logic operations jump out of the expression
>> path to the non-expression path.
>>
>> Unfortunately, this meant that we would first accept() the two operands,
>> skip generating any code that used them, then accept() the whole
>> expression, generating code for the operands a second time.
>>
>> Dead code elimination would always remove the first set of redundant
>> operand assembly, since nothing actually used them.  But we shouldn't
>> generate it in the first place.
>>
>> Signed-off-by: Kenneth Graunke <kenneth at whitecape.org>
>> Cc: Matt Turner <mattst88 at gmail.com>
>> Cc: Eric Anholt <eric at anholt.net>
>> ---
> 
> Both patches are
> Reviewed-by: Matt Turner <mattst88 at gmail.com>
> 
> For posterity, this patch was preventing my addc+add -> addc peephole
> from working. Thanks for tracking this down.
> 
> Matt

Thanks Matt!