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target/arm: Implement FPCR.AH semantics for scalar FMIN/FMAX

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When FPCR.AH == 1, floating point FMIN and FMAX have some odd special
cases:

 * comparing two zeroes (even of different sign) or comparing a NaN
   with anything always returns the second argument (possibly
   squashed to zero)
 * denormal outputs are not squashed to zero regardless of FZ or FZ16

Implement these semantics in new helper functions and select them at
translate time if FPCR.AH is 1 for the scalar FMAX and FMIN insns.
(We will convert the other FMAX and FMIN insns in subsequent
commits.)

Note that FMINNM and FMAXNM are not affected.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Peter Maydell 2025-02-01 16:39:27 +00:00
parent 7bcde0c6dd
commit 2a734f3fe3
3 changed files with 64 additions and 2 deletions
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36
target/arm/tcg/helper-a64.c
View File

@ -399,6 +399,42 @@ float32 HELPER(fcvtx_f64_to_f32)(float64 a, float_status *fpst)
return r;
}
/*
* AH=1 min/max have some odd special cases:
* comparing two zeroes (regardless of sign), (NaN, anything),
* or (anything, NaN) should return the second argument (possibly
* squashed to zero).
* Also, denormal outputs are not squashed to zero regardless of FZ or FZ16.
*/
#define AH_MINMAX_HELPER(NAME, CTYPE, FLOATTYPE, MINMAX) \
CTYPE HELPER(NAME)(CTYPE a, CTYPE b, float_status *fpst) \
{ \
bool save; \
CTYPE r; \
a = FLOATTYPE ## _squash_input_denormal(a, fpst); \
b = FLOATTYPE ## _squash_input_denormal(b, fpst); \
if (FLOATTYPE ## _is_zero(a) && FLOATTYPE ## _is_zero(b)) { \
return b; \
} \
if (FLOATTYPE ## _is_any_nan(a) || \
FLOATTYPE ## _is_any_nan(b)) { \
float_raise(float_flag_invalid, fpst); \
return b; \
} \
save = get_flush_to_zero(fpst); \
set_flush_to_zero(false, fpst); \
r = FLOATTYPE ## _ ## MINMAX(a, b, fpst); \
set_flush_to_zero(save, fpst); \
return r; \
}
AH_MINMAX_HELPER(vfp_ah_minh, dh_ctype_f16, float16, min)
AH_MINMAX_HELPER(vfp_ah_mins, float32, float32, min)
AH_MINMAX_HELPER(vfp_ah_mind, float64, float64, min)
AH_MINMAX_HELPER(vfp_ah_maxh, dh_ctype_f16, float16, max)
AH_MINMAX_HELPER(vfp_ah_maxs, float32, float32, max)
AH_MINMAX_HELPER(vfp_ah_maxd, float64, float64, max)
/* 64-bit versions of the CRC helpers. Note that although the operation
* (and the prototypes of crc32c() and crc32() mean that only the bottom
* 32 bits of the accumulator and result are used, we pass and return

7
target/arm/tcg/helper-a64.h
View File

@ -67,6 +67,13 @@ DEF_HELPER_4(advsimd_muladd2h, i32, i32, i32, i32, fpst)
DEF_HELPER_2(advsimd_rinth_exact, f16, f16, fpst)
DEF_HELPER_2(advsimd_rinth, f16, f16, fpst)
DEF_HELPER_3(vfp_ah_minh, f16, f16, f16, fpst)
DEF_HELPER_3(vfp_ah_mins, f32, f32, f32, fpst)
DEF_HELPER_3(vfp_ah_mind, f64, f64, f64, fpst)
DEF_HELPER_3(vfp_ah_maxh, f16, f16, f16, fpst)
DEF_HELPER_3(vfp_ah_maxs, f32, f32, f32, fpst)
DEF_HELPER_3(vfp_ah_maxd, f64, f64, f64, fpst)
DEF_HELPER_2(exception_return, void, env, i64)
DEF_HELPER_FLAGS_2(dc_zva, TCG_CALL_NO_WG, void, env, i64)

23
target/arm/tcg/translate-a64.c
View File

@ -5141,6 +5141,15 @@ static bool do_fp3_scalar_ah(DisasContext *s, arg_rrr_e *a, const FPScalar *f,
select_ah_fpst(s, a->esz));
}
/* Some insns need to call different helpers when FPCR.AH == 1 */
static bool do_fp3_scalar_2fn(DisasContext *s, arg_rrr_e *a,
const FPScalar *fnormal,
const FPScalar *fah,
int mergereg)
{
return do_fp3_scalar(s, a, s->fpcr_ah ? fah : fnormal, mergereg);
}
static const FPScalar f_scalar_fadd = {
gen_helper_vfp_addh,
gen_helper_vfp_adds,
@ -5174,14 +5183,24 @@ static const FPScalar f_scalar_fmax = {
gen_helper_vfp_maxs,
gen_helper_vfp_maxd,
};
TRANS(FMAX_s, do_fp3_scalar, a, &f_scalar_fmax, a->rn)
static const FPScalar f_scalar_fmax_ah = {
gen_helper_vfp_ah_maxh,
gen_helper_vfp_ah_maxs,
gen_helper_vfp_ah_maxd,
};
TRANS(FMAX_s, do_fp3_scalar_2fn, a, &f_scalar_fmax, &f_scalar_fmax_ah, a->rn)
static const FPScalar f_scalar_fmin = {
gen_helper_vfp_minh,
gen_helper_vfp_mins,
gen_helper_vfp_mind,
};
TRANS(FMIN_s, do_fp3_scalar, a, &f_scalar_fmin, a->rn)
static const FPScalar f_scalar_fmin_ah = {
gen_helper_vfp_ah_minh,
gen_helper_vfp_ah_mins,
gen_helper_vfp_ah_mind,
};
TRANS(FMIN_s, do_fp3_scalar_2fn, a, &f_scalar_fmin, &f_scalar_fmin_ah, a->rn)
static const FPScalar f_scalar_fmaxnm = {
gen_helper_vfp_maxnumh,