[Mesa-dev] [PATCH 01/16] glsl: Add EmitNoSaturate to shader compiler options

Matt Turner mattst88 at gmail.com
Sun Nov 16 19:34:53 PST 2014

On Sun, Nov 16, 2014 at 7:33 PM, Matt Turner <mattst88 at gmail.com> wrote:
> On Sun, Nov 16, 2014 at 5:51 PM, Thomas Helland
> <thomashelland90 at gmail.com> wrote:
>> This allows the backend to decide if it does not
>> want saturates, or if it wants to combine min/max
>> together by itself.
>> Usefull for drivers that implement saturate with min/max
>> as it can allow for some optimizations by min/max-pruning.
>> Drivers like freedreno and vc4 will benefit.
>> ---
>> I have not made any drivers set the option.
>> Probably some pipe-cap or something is needed
>> in gallium to allow this?
>> I could possibly find time to do a follow-up
>> patch for this if someone leads me in the right direction.
>> saturate() in ir_builder generates ir_unop_saturate unconditionally.
>> If someone comes along later and does saturate()
>> in some optimization pass, whithout checking the options,
>> they will mess up possible optimizations for some backends.
>> The cleanest way I could find for always doing the right
>> thing was to write a lowering pass in opt_algebraic to
>> lower ir_unop_sature into max(min(x, 1), 0);
> We already have that, so no need for work in that area :)
> See lower_instructions_visitor::sat_to_clamp().

... and as a result the second hunk of this patch isn't needed.

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