[Mesa-dev] [PATCH 1/2] nvc0/ir: detect AND/SHR pairs and convert into EXTBF

[Eric Anholt]

Matt Turner <mattst88 at gmail.com> writes:

> On Tue, Aug 18, 2015 at 6:49 PM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>> Some shaders appear to extract bits using shift/and combos. Detect
>> (some) of those and convert to EXTBF instead.
>
> What is EXTBF? Extract byte to float?
>
> I ask because Unigine Heaven has shaders that pack 3x byte-integers
> into one component of a vec4 and extracts them with shifts/ands and
> converts them to floats, and i965 could do the extraction and
> conversion in a single instruction. I'm curious if this is the same
> thing you're optimizing.
>
> I thought about adding an extract_byte(src, byte_num) operation, but
> i965's copy propagation caused me some headache and I shelved it.

I could use this one, as int, uint, and unorm unpacks.  Right now for
int/uint I'm recognizing the pattern in vc4_program.c (in a branch).
I'd be interested in writing the NIR bits if others are interested in
having this.
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