[PULL 35/36] target/arm: Use FPST_A64_F16 for halfprec-to-other conversions

[Peter Maydell]

We should be using the F16-specific float_status for conversions from
half-precision, because halfprec inputs never set Input Denormal.

Without FEAT_AHP, using the wrong fpst here had no effect, because
the only difference between the A64_F16 and A64 fpst is its handling
of flush-to-zero on input and output, and the helper functions
vfp_fcvt_f16_to_* and vfp_fcvt_*_to_f16 all explicitly squash the
relevant flushing flags, and flush_inputs_to_zero was the only way
that IDC could be set.

With FEAT_AHP, the FPCR.AH=1 behaviour sets IDC for
input_denormal_used, which we will only ignore in
vfp_get_fpsr_from_host() for the A64_F16 fpst; so it matters that we
use that one for f16 inputs (and the normal one for single/double to
f16 conversions).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250124162836.2332150-27-peter.maydell@linaro.org
---
 target/arm/tcg/translate-a64.c | 9 ++++++---
 target/arm/tcg/translate-sve.c | 4 ++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/target/arm/tcg/translate-a64.c b/target/arm/tcg/translate-a64.c
index 703f265f20e..0b76a2cdb78 100644
--- a/target/arm/tcg/translate-a64.c
+++ b/target/arm/tcg/translate-a64.c
@@ -8568,7 +8568,7 @@ static bool trans_FCVT_s_sh(DisasContext *s, arg_rr *a)
     if (fp_access_check(s)) {
         TCGv_i32 tcg_rn = read_fp_hreg(s, a->rn);
         TCGv_i32 tcg_rd = tcg_temp_new_i32();
-        TCGv_ptr tcg_fpst = fpstatus_ptr(FPST_A64);
+        TCGv_ptr tcg_fpst = fpstatus_ptr(FPST_A64_F16);
         TCGv_i32 tcg_ahp = get_ahp_flag();
 
         gen_helper_vfp_fcvt_f16_to_f32(tcg_rd, tcg_rn, tcg_fpst, tcg_ahp);
@@ -8582,7 +8582,7 @@ static bool trans_FCVT_s_dh(DisasContext *s, arg_rr *a)
     if (fp_access_check(s)) {
         TCGv_i32 tcg_rn = read_fp_hreg(s, a->rn);
         TCGv_i64 tcg_rd = tcg_temp_new_i64();
-        TCGv_ptr tcg_fpst = fpstatus_ptr(FPST_A64);
+        TCGv_ptr tcg_fpst = fpstatus_ptr(FPST_A64_F16);
         TCGv_i32 tcg_ahp = get_ahp_flag();
 
         gen_helper_vfp_fcvt_f16_to_f64(tcg_rd, tcg_rn, tcg_fpst, tcg_ahp);
@@ -9511,13 +9511,14 @@ static bool trans_FCVTL_v(DisasContext *s, arg_qrr_e *a)
         return true;
     }
 
-    fpst = fpstatus_ptr(FPST_A64);
     if (a->esz == MO_64) {
         /* 32 -> 64 bit fp conversion */
         TCGv_i64 tcg_res[2];
         TCGv_i32 tcg_op = tcg_temp_new_i32();
         int srcelt = a->q ? 2 : 0;
 
+        fpst = fpstatus_ptr(FPST_A64);
+
         for (pass = 0; pass < 2; pass++) {
             tcg_res[pass] = tcg_temp_new_i64();
             read_vec_element_i32(s, tcg_op, a->rn, srcelt + pass, MO_32);
@@ -9532,6 +9533,8 @@ static bool trans_FCVTL_v(DisasContext *s, arg_qrr_e *a)
         TCGv_i32 tcg_res[4];
         TCGv_i32 ahp = get_ahp_flag();
 
+        fpst = fpstatus_ptr(FPST_A64_F16);
+
         for (pass = 0; pass < 4; pass++) {
             tcg_res[pass] = tcg_temp_new_i32();
             read_vec_element_i32(s, tcg_res[pass], a->rn, srcelt + pass, 
MO_16);
diff --git a/target/arm/tcg/translate-sve.c b/target/arm/tcg/translate-sve.c
index a7dbea5acd0..e1788330aa7 100644
--- a/target/arm/tcg/translate-sve.c
+++ b/target/arm/tcg/translate-sve.c
@@ -3887,7 +3887,7 @@ TRANS_FEAT(FCMLA_zzxz, aa64_sve, gen_gvec_fpst_zzzz, 
fcmla_idx_fns[a->esz],
 TRANS_FEAT(FCVT_sh, aa64_sve, gen_gvec_fpst_arg_zpz,
            gen_helper_sve_fcvt_sh, a, 0, FPST_A64)
 TRANS_FEAT(FCVT_hs, aa64_sve, gen_gvec_fpst_arg_zpz,
-           gen_helper_sve_fcvt_hs, a, 0, FPST_A64)
+           gen_helper_sve_fcvt_hs, a, 0, FPST_A64_F16)
 
 TRANS_FEAT(BFCVT, aa64_sve_bf16, gen_gvec_fpst_arg_zpz,
            gen_helper_sve_bfcvt, a, 0, FPST_A64)
@@ -3895,7 +3895,7 @@ TRANS_FEAT(BFCVT, aa64_sve_bf16, gen_gvec_fpst_arg_zpz,
 TRANS_FEAT(FCVT_dh, aa64_sve, gen_gvec_fpst_arg_zpz,
            gen_helper_sve_fcvt_dh, a, 0, FPST_A64)
 TRANS_FEAT(FCVT_hd, aa64_sve, gen_gvec_fpst_arg_zpz,
-           gen_helper_sve_fcvt_hd, a, 0, FPST_A64)
+           gen_helper_sve_fcvt_hd, a, 0, FPST_A64_F16)
 TRANS_FEAT(FCVT_ds, aa64_sve, gen_gvec_fpst_arg_zpz,
            gen_helper_sve_fcvt_ds, a, 0, FPST_A64)
 TRANS_FEAT(FCVT_sd, aa64_sve, gen_gvec_fpst_arg_zpz,
-- 
2.34.1