niansa-misc/glibc
1
0
Fork 0
mirror of git://sourceware.org/git/glibc.git synced 2025-03-06 20:58:33 +01:00
Code Issues Projects Releases Packages Wiki Activity

AArch64: Improve codegen in SVE expm1f and users

Browse source 
Use unpredicated muls, use absolute compare and improve memory access.
Expm1f, sinhf and tanhf show 7%, 5% and 1% improvement in throughput
microbenchmark on Neoverse V1.

(cherry picked from commit f86b4cf875)
This commit is contained in:
Luna Lamb 2025-01-03 20:15:17 +00:00 • committed by Wilco Dijkstra
parent aa7c61ea15
commit d983f14c30
4 changed files with 44 additions and 45 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

31
sysdeps/aarch64/fpu/expm1f_sve.c
View file

@ -18,7 +18,6 @@
<https://www.gnu.org/licenses/>. */
#include "sv_math.h"
#include "poly_sve_f32.h"
/* Largest value of x for which expm1(x) should round to -1. */
#define SpecialBound 0x1.5ebc4p+6f
@ -28,20 +27,17 @@ static const struct data
/* These 4 are grouped together so they can be loaded as one quadword, then
used with _lane forms of svmla/svmls. */
float c2, c4, ln2_hi, ln2_lo;
float c0, c1, c3, inv_ln2, special_bound, shift;
float c0, inv_ln2, c1, c3, special_bound;
} data = {
/* Generated using fpminimax. */
.c0 = 0x1.fffffep-2, .c1 = 0x1.5554aep-3,
.c2 = 0x1.555736p-5, .c3 = 0x1.12287cp-7,
.c4 = 0x1.6b55a2p-10,
.c4 = 0x1.6b55a2p-10, .inv_ln2 = 0x1.715476p+0f,
.special_bound = SpecialBound, .ln2_lo = 0x1.7f7d1cp-20f,
.ln2_hi = 0x1.62e4p-1f,
.special_bound = SpecialBound, .shift = 0x1.8p23f,
.inv_ln2 = 0x1.715476p+0f, .ln2_hi = 0x1.62e4p-1f,
.ln2_lo = 0x1.7f7d1cp-20f,
};
#define C(i) sv_f32 (d->c##i)
static svfloat32_t NOINLINE
special_case (svfloat32_t x, svbool_t pg)
{
@ -71,9 +67,8 @@ svfloat32_t SV_NAME_F1 (expm1) (svfloat32_t x, svbool_t pg)
and f = x - i * ln2, then f is in [-ln2/2, ln2/2].
exp(x) - 1 = 2^i * (expm1(f) + 1) - 1
where 2^i is exact because i is an integer. */
svfloat32_t j = svmla_x (pg, sv_f32 (d->shift), x, d->inv_ln2);
j = svsub_x (pg, j, d->shift);
svint32_t i = svcvt_s32_x (pg, j);
svfloat32_t j = svmul_x (svptrue_b32 (), x, d->inv_ln2);
j = svrinta_x (pg, j);
svfloat32_t f = svmls_lane (x, j, lane_constants, 2);
f = svmls_lane (f, j, lane_constants, 3);
@ -83,17 +78,17 @@ svfloat32_t SV_NAME_F1 (expm1) (svfloat32_t x, svbool_t pg)
x + ax^2 + bx^3 + cx^4 ....
So we calculate the polynomial P(f) = a + bf + cf^2 + ...
and assemble the approximation expm1(f) ~= f + f^2 * P(f). */
svfloat32_t p12 = svmla_lane (C (1), f, lane_constants, 0);
svfloat32_t p34 = svmla_lane (C (3), f, lane_constants, 1);
svfloat32_t f2 = svmul_x (pg, f, f);
svfloat32_t p12 = svmla_lane (sv_f32 (d->c1), f, lane_constants, 0);
svfloat32_t p34 = svmla_lane (sv_f32 (d->c3), f, lane_constants, 1);
svfloat32_t f2 = svmul_x (svptrue_b32 (), f, f);
svfloat32_t p = svmla_x (pg, p12, f2, p34);
p = svmla_x (pg, C (0), f, p);
p = svmla_x (pg, sv_f32 (d->c0), f, p);
p = svmla_x (pg, f, f2, p);
/* Assemble the result.
expm1(x) ~= 2^i * (p + 1) - 1
Let t = 2^i. */
svfloat32_t t = svreinterpret_f32 (
svadd_x (pg, svreinterpret_u32 (svlsl_x (pg, i, 23)), 0x3f800000));
return svmla_x (pg, svsub_x (pg, t, 1), p, t);
svfloat32_t t = svscale_x (pg, sv_f32 (1.0f), svcvt_s32_x (pg, j));
return svmla_x (pg, svsub_x (pg, t, 1.0f), p, t);
}

2
sysdeps/aarch64/fpu/sinhf_sve.c
View file

@ -63,5 +63,5 @@ svfloat32_t SV_NAME_F1 (sinh) (svfloat32_t x, const svbool_t pg)
if (__glibc_unlikely (svptest_any (pg, special)))
return special_case (x, svmul_x (pg, t, halfsign), special);
return svmul_x (pg, t, halfsign);
return svmul_x (svptrue_b32 (), t, halfsign);
}

28
sysdeps/aarch64/fpu/sv_expm1f_inline.h
View file

@ -27,21 +27,18 @@ struct sv_expm1f_data
/* These 4 are grouped together so they can be loaded as one quadword, then
used with _lane forms of svmla/svmls. */
float32_t c2, c4, ln2_hi, ln2_lo;
float32_t c0, c1, c3, inv_ln2, shift;
float c0, inv_ln2, c1, c3, special_bound;
};
/* Coefficients generated using fpminimax. */
#define SV_EXPM1F_DATA \
{ \
.c0 = 0x1.fffffep-2, .c1 = 0x1.5554aep-3, .c2 = 0x1.555736p-5, \
.c3 = 0x1.12287cp-7, .c4 = 0x1.6b55a2p-10, \
.c0 = 0x1.fffffep-2, .c1 = 0x1.5554aep-3, .inv_ln2 = 0x1.715476p+0f, \
.c2 = 0x1.555736p-5, .c3 = 0x1.12287cp-7, \
\
.shift = 0x1.8p23f, .inv_ln2 = 0x1.715476p+0f, .ln2_hi = 0x1.62e4p-1f, \
.ln2_lo = 0x1.7f7d1cp-20f, \
.c4 = 0x1.6b55a2p-10, .ln2_lo = 0x1.7f7d1cp-20f, .ln2_hi = 0x1.62e4p-1f, \
}
#define C(i) sv_f32 (d->c##i)
static inline svfloat32_t
expm1f_inline (svfloat32_t x, svbool_t pg, const struct sv_expm1f_data *d)
{
@ -55,9 +52,8 @@ expm1f_inline (svfloat32_t x, svbool_t pg, const struct sv_expm1f_data *d)
and f = x - i * ln2, then f is in [-ln2/2, ln2/2].
exp(x) - 1 = 2^i * (expm1(f) + 1) - 1
where 2^i is exact because i is an integer. */
svfloat32_t j = svmla_x (pg, sv_f32 (d->shift), x, d->inv_ln2);
j = svsub_x (pg, j, d->shift);
svint32_t i = svcvt_s32_x (pg, j);
svfloat32_t j = svmul_x (svptrue_b32 (), x, d->inv_ln2);
j = svrinta_x (pg, j);
svfloat32_t f = svmls_lane (x, j, lane_constants, 2);
f = svmls_lane (f, j, lane_constants, 3);
@ -67,18 +63,18 @@ expm1f_inline (svfloat32_t x, svbool_t pg, const struct sv_expm1f_data *d)
x + ax^2 + bx^3 + cx^4 ....
So we calculate the polynomial P(f) = a + bf + cf^2 + ...
and assemble the approximation expm1(f) ~= f + f^2 * P(f). */
svfloat32_t p12 = svmla_lane (C (1), f, lane_constants, 0);
svfloat32_t p34 = svmla_lane (C (3), f, lane_constants, 1);
svfloat32_t f2 = svmul_x (pg, f, f);
svfloat32_t p12 = svmla_lane (sv_f32 (d->c1), f, lane_constants, 0);
svfloat32_t p34 = svmla_lane (sv_f32 (d->c3), f, lane_constants, 1);
svfloat32_t f2 = svmul_x (svptrue_b32 (), f, f);
svfloat32_t p = svmla_x (pg, p12, f2, p34);
p = svmla_x (pg, C (0), f, p);
p = svmla_x (pg, sv_f32 (d->c0), f, p);
p = svmla_x (pg, f, f2, p);
/* Assemble the result.
expm1(x) ~= 2^i * (p + 1) - 1
Let t = 2^i. */
svfloat32_t t = svscale_x (pg, sv_f32 (1), i);
return svmla_x (pg, svsub_x (pg, t, 1), p, t);
svfloat32_t t = svscale_x (pg, sv_f32 (1.0f), svcvt_s32_x (pg, j));
return svmla_x (pg, svsub_x (pg, t, 1.0f), p, t);
}
#endif

28
sysdeps/aarch64/fpu/tanhf_sve.c
View file

@ -19,20 +19,27 @@
#include "sv_expm1f_inline.h"
/* Largest value of x for which tanhf(x) rounds to 1 (or -1 for negative). */
#define BoringBound 0x1.205966p+3f
static const struct data
{
struct sv_expm1f_data expm1f_consts;
uint32_t boring_bound, onef;
uint32_t onef, special_bound;
float boring_bound;
} data = {
.expm1f_consts = SV_EXPM1F_DATA,
/* 0x1.205966p+3, above which tanhf rounds to 1 (or -1 for negative). */
.boring_bound = 0x41102cb3,
.onef = 0x3f800000,
.special_bound = 0x7f800000,
.boring_bound = BoringBound,
};
static svfloat32_t NOINLINE
special_case (svfloat32_t x, svfloat32_t y, svbool_t special)
special_case (svfloat32_t x, svbool_t pg, svbool_t is_boring,
svfloat32_t boring, svfloat32_t q, svbool_t special)
{
svfloat32_t y
= svsel_f32 (is_boring, boring, svdiv_x (pg, q, svadd_x (pg, q, 2.0)));
return sv_call_f32 (tanhf, x, y, special);
}
@ -47,15 +54,16 @@ svfloat32_t SV_NAME_F1 (tanh) (svfloat32_t x, const svbool_t pg)
svfloat32_t ax = svabs_x (pg, x);
svuint32_t iax = svreinterpret_u32 (ax);
svuint32_t sign = sveor_x (pg, svreinterpret_u32 (x), iax);
svbool_t is_boring = svcmpgt (pg, iax, d->boring_bound);
svfloat32_t boring = svreinterpret_f32 (svorr_x (pg, sign, d->onef));
svbool_t special = svcmpgt (pg, iax, 0x7f800000);
svbool_t special = svcmpgt (pg, iax, d->special_bound);
svbool_t is_boring = svacgt (pg, x, d->boring_bound);
/* tanh(x) = (e^2x - 1) / (e^2x + 1). */
svfloat32_t q = expm1f_inline (svmul_x (pg, x, 2.0), pg, &d->expm1f_consts);
svfloat32_t y = svdiv_x (pg, q, svadd_x (pg, q, 2.0));
svfloat32_t q = expm1f_inline (svmul_x (svptrue_b32 (), x, 2.0), pg,
&d->expm1f_consts);
if (__glibc_unlikely (svptest_any (pg, special)))
return special_case (x, svsel_f32 (is_boring, boring, y), special);
return special_case (x, pg, is_boring, boring, q, special);
svfloat32_t y = svdiv_x (pg, q, svadd_x (pg, q, 2.0));
return svsel_f32 (is_boring, boring, y);
}