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nir: push down fabs for atan

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worse in terms of NIR instruction count but lets the fabs fold easier. (on agx,
which has fabs on comparisons and fmul but not on bcsel. should be no worse if
ISA has fabs on all 3.)

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30934>
This commit is contained in:
Alyssa Rosenzweig 2024-08-29 19:13:08 -04:00 • committed by Marge Bot
parent 8579375777
commit 0a4a0df283
1 changed files with 9 additions and 7 deletions
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16
src/compiler/nir/nir_builtin_builder.c
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@ -170,12 +170,14 @@ nir_atan(nir_builder *b, nir_def *y_over_x)
/*
* range-reduction, first step:
*
* / |y_over_x| if |y_over_x| <= 1.0;
* x = <
* \ 1.0 / |y_over_x| otherwise
* / y_over_x if |y_over_x| <= 1.0;
* u = <
* \ 1.0 / y_over_x otherwise
*
* x = |u| for the corrected sign.
*/
nir_def *x = nir_bcsel(b, nir_fle_imm(b, abs_y_over_x, 1.0),
abs_y_over_x, nir_frcp(b, abs_y_over_x));
nir_def *u = nir_bcsel(b, nir_fle_imm(b, abs_y_over_x, 1.0),
y_over_x, nir_frcp(b, y_over_x));
/*
* approximate atan by evaluating polynomial using Horner's method:
@ -190,14 +192,14 @@ nir_atan(nir_builder *b, nir_def *y_over_x)
-0.3326756418091246f, 0.9999793128310355f
};
nir_def *x_2 = nir_fmul(b, x, x);
nir_def *x_2 = nir_fmul(b, u, u);
nir_def *res = nir_imm_floatN_t(b, coeffs[0], bit_size);
for (unsigned i = 1; i < ARRAY_SIZE(coeffs); ++i) {
res = nir_ffma_imm2(b, res, x_2, coeffs[i]);
}
nir_def *tmp = nir_fmul(b, x, res);
nir_def *tmp = nir_fmul(b, nir_fabs(b, u), res);
/* range-reduction fixup */
tmp = nir_ffma(b,