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nir: add fmad_or_ffma helpers and use it in lower_double_ops

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We skip emitting ffma_weak here, because otherwise we'd require a lowering
loop with opt_algebraic and lower_double_ops and this way it's also
cheaper.

Reviewed-by: Georg Lehmann <dadschoorse@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/41165>
This commit is contained in:
Karol Herbst 2026-05-04 20:56:23 +02:00 • committed by Marge Bot
parent eb817b1f63
commit aeea2e7c1f
1 changed files with 26 additions and 10 deletions
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36
src/compiler/nir/nir_lower_double_ops.c
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@ -29,6 +29,22 @@
#include <float.h>
#include <math.h>
static nir_def *
nir_fmad_or_ffma(nir_builder *build, nir_def *src0, nir_def *src1,
nir_def *src2)
{
if (nir_prefers_fmad(build->shader, src0->bit_size))
return nir_fadd(build, nir_fmul(build, src0, src1), src2);
else
return nir_ffma(build, src0, src1, src2);
}
static nir_def *
nir_fmad_or_fma_imm2(nir_builder *build, nir_def *src0, nir_def *src1, double src2)
{
return nir_fmad_or_ffma(build, src0, src1, nir_imm_floatN_t(build, src2, src0->bit_size));
}
/*
* Lowers some unsupported double operations, using only:
*
@ -172,8 +188,8 @@ lower_rcp(nir_builder *b, nir_def *src)
* See https://en.wikipedia.org/wiki/Division_algorithm for more details.
*/
ra = nir_ffma_old(b, nir_fneg(b, ra), nir_ffma_imm2(b, ra, src, -1), ra);
ra = nir_ffma_old(b, nir_fneg(b, ra), nir_ffma_imm2(b, ra, src, -1), ra);
ra = nir_fmad_or_ffma(b, nir_fneg(b, ra), nir_fmad_or_fma_imm2(b, ra, src, -1), ra);
ra = nir_fmad_or_ffma(b, nir_fneg(b, ra), nir_fmad_or_fma_imm2(b, ra, src, -1), ra);
return fix_inv_result(b, ra, src, new_exp);
}
@ -299,18 +315,18 @@ lower_sqrt_rsq(nir_builder *b, nir_def *src, bool sqrt)
nir_def *one_half = nir_imm_double(b, 0.5);
nir_def *h_0 = nir_fmul(b, one_half, ra);
nir_def *g_0 = nir_fmul(b, src, ra);
nir_def *r_0 = nir_ffma_old(b, nir_fneg(b, h_0), g_0, one_half);
nir_def *h_1 = nir_ffma_old(b, h_0, r_0, h_0);
nir_def *r_0 = nir_fmad_or_ffma(b, nir_fneg(b, h_0), g_0, one_half);
nir_def *h_1 = nir_fmad_or_ffma(b, h_0, r_0, h_0);
nir_def *res;
if (sqrt) {
nir_def *g_1 = nir_ffma_old(b, g_0, r_0, g_0);
nir_def *r_1 = nir_ffma_old(b, nir_fneg(b, g_1), g_1, src);
res = nir_ffma_old(b, h_1, r_1, g_1);
nir_def *g_1 = nir_fmad_or_ffma(b, g_0, r_0, g_0);
nir_def *r_1 = nir_fmad_or_ffma(b, nir_fneg(b, g_1), g_1, src);
res = nir_fmad_or_ffma(b, h_1, r_1, g_1);
} else {
nir_def *y_1 = nir_fmul_imm(b, h_1, 2.0);
nir_def *r_1 = nir_ffma_old(b, nir_fneg(b, y_1), nir_fmul(b, h_1, src),
one_half);
res = nir_ffma_old(b, y_1, r_1, y_1);
nir_def *r_1 = nir_fmad_or_ffma(b, nir_fneg(b, y_1), nir_fmul(b, h_1, src),
one_half);
res = nir_fmad_or_ffma(b, y_1, r_1, y_1);
}
if (sqrt) {