On 03/24/2015 05:01 AM, Tapani Pälli wrote:
>
> On 03/20/2015 10:58 PM, Ian Romanick wrote:
>> From: Ian Romanick <ian.d.roman...@intel.com>
>>
>> With previous changes to emit more ir_triop_csel, the i965 channel
>> expressions pass can generate sequences like:
>>
>> mov(8) g45<1>F 1F
>> (+f0) sel(8) g40<1>F g45<8,8,1>F 1F
>>
>> There are no shader-db changes now, but this prevents a large number of
>> regressions from a later commit (glsl: Optimize certain if-statements to
>> ir_triop_csel).
>>
>> Signed-off-by: Ian Romanick <ian.d.roman...@intel.com>
>> Cc: Tapani Pälli <tapani.pa...@intel.com>
>> ---
>> src/mesa/drivers/dri/i965/brw_fs_visitor.cpp | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
>> b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
>> index e39dab3..1fbef5f 100644
>> --- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
>> +++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
>> @@ -708,6 +708,15 @@ fs_visitor::visit(ir_expression *ir)
>> break;
>>
>> case ir_triop_csel:
>> + /* After splitting an expression like 'v = csel(cond, vec4(a,
>> b, c, 1),
>> + * vec4(d, e, f, 1))', there will be a 'v.w = csel(cond, 1,
>> 1)'. Detect
>> + * this, and avoid emitting the spurious SEL.
>> + */
>> + if (ir->operands[1]->equals(ir->operands[2])) {
>> + ir->operands[1]->accept(this);
>> + return;
>
> The result is correct but why is this done in the backend? Couldn't the
> later commit mentioned for glsl already detect this or maybe additional
> optimization pass there?
I had assumed there was already an algebraic optimization for this case
that, for whatever reason, just wasn't triggering here. I went to go
find it, and it does not exist... it looks like replacing this code with
a similar change to src/glsl/opt_algebraic.cpp is equally effective.
I'll do that instead.
>> + }
>> +
>> if (try_opt_frontfacing_ternary(ir))
>> return;
>>
>>
>
> // Tapani
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