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nir: Add Mali-specific derivative opcodes 

Add derivative opcodes fddx_must_abs_mali/fddy_must_abs_mali satisfying:

   fabs(fdd*_must_abs_mali(v)) = fabs(fdd*(v))

The sign of their result is undefined.

On Bifrost and Valhall, these unsigned derivatives can be implemented
more efficiently than the correctly-signed counterparts, since the sign
fixup requires extra ALU instructions. On backends where this is the
case, it is useful to optimize fabs(fdd*(v)) to
fabs(fdd*_must_abs_mali(v)). This pattern comes up with the GLSL builtin
`fwidth`.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12332>
This commit is contained in:
Alyssa Rosenzweig 2021-10-02 09:02:19 -04:00 committed by Marge Bot
parent 72c0e57e7e
commit 3e8f540753
1 changed files with 4 additions and 0 deletions
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4
src/compiler/nir/nir_opcodes.py
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@ -1308,6 +1308,10 @@ for (int i = 0; i < 32; i += 8) {
unop("fsat_signed_mali", tfloat, ("fmin(fmax(src0, -1.0), 1.0)"))
unop("fclamp_pos_mali", tfloat, ("fmax(src0, 0.0)"))
# Magnitude equal to fddx/y, sign undefined. Derivative of a constant is zero.
unop("fddx_must_abs_mali", tfloat, "0.0")
unop("fddy_must_abs_mali", tfloat, "0.0")
# DXIL specific double [un]pack
# DXIL doesn't support generic [un]pack instructions, so we want those
# lowered to bit ops. HLSL doesn't support 64bit bitcasts to/from