target/arm: Replace ARM_FEATURE_VFP4 with isar_feature_aa32_simdfmac

All remaining tests for VFP4 are for fused multiply-add insns.

Since the MVFR1 field is used for both VFP and NEON, move its adjustment
from the !has_neon block to the (!has_vfp && !has_neon) block.

Test for vfp of the appropraite width alongside the test for simdfmac
within translate-vfp.inc.c. Within disas_neon_data_insn, we have
already tested for ARM_FEATURE_NEON.

Backports commit c52881bbc22b50db99a6c37171ad3eea7d959ae6 from qemu

qemu/target/arm/cpu.h

@@ -3387,6 +3387,18 @@ static inline bool isar_feature_aa32_fp16_dpconv(const ARMISARegisters *id)
     return FIELD_EX32(id->mvfr1, MVFR1, FPHP) > 1;
 }
 
+/*
+ * Note that this ID register field covers both VFP and Neon FMAC,
+ * so should usually be tested in combination with some other
+ * check that confirms the presence of whichever of VFP or Neon is
+ * relevant, to avoid accidentally enabling a Neon feature on
+ * a VFP-no-Neon core or vice-versa.
+ */
+static inline bool isar_feature_aa32_simdfmac(const ARMISARegisters *id)
+{
+    return FIELD_EX32(id->mvfr1, MVFR1, SIMDFMAC) != 0;
+}
+
 static inline bool isar_feature_aa32_vsel(const ARMISARegisters *id)
 {
     return FIELD_EX32(id->mvfr2, MVFR2, FPMISC) >= 1;

qemu/target/arm/translate-vfp.inc.c

@@ -1828,11 +1828,19 @@ static bool trans_VFM_sp(DisasContext *s, arg_VFM_sp *a)
 
     /*
      * Present in VFPv4 only.
+     * Note that we can't rely on the SIMDFMAC check alone, because
+     * in a Neon-no-VFP core that ID register field will be non-zero.
+     */
+    if (!dc_isar_feature(aa32_simdfmac, s) ||
+        !dc_isar_feature(aa32_fpsp_v2, s)) {
+        return false;
+    }
+
+    /*
      * In v7A, UNPREDICTABLE with non-zero vector length/stride; from
      * v8A, must UNDEF. We choose to UNDEF for both v7A and v8A.
      */
-    if (!arm_dc_feature(s, ARM_FEATURE_VFP4) ||
+    if (s->vec_len != 0 || s->vec_stride != 0) {
-        (s->vec_len != 0 || s->vec_stride != 0)) {
         return false;
     }
 
@@ -1887,11 +1895,19 @@ static bool trans_VFM_dp(DisasContext *s, arg_VFM_dp *a)
 
     /*
      * Present in VFPv4 only.
+     * Note that we can't rely on the SIMDFMAC check alone, because
+     * in a Neon-no-VFP core that ID register field will be non-zero.
+     */
+    if (!dc_isar_feature(aa32_simdfmac, s) ||
+        !dc_isar_feature(aa32_fpdp_v2, s)) {
+        return false;
+    }
+
+    /*
      * In v7A, UNPREDICTABLE with non-zero vector length/stride; from
      * v8A, must UNDEF. We choose to UNDEF for both v7A and v8A.
      */
-    if (!arm_dc_feature(s, ARM_FEATURE_VFP4) ||
+    if (s->vec_len != 0 || s->vec_stride != 0) {
-        (s->vec_len != 0 || s->vec_stride != 0)) {
         return false;
     }
 

qemu/target/arm/translate.c

@@ -5283,7 +5283,7 @@ static int disas_neon_data_insn(DisasContext *s, uint32_t insn)
             }
             break;
         case NEON_3R_VFM_VQRDMLSH:
-            if (!arm_dc_feature(s, ARM_FEATURE_VFP4)) {
+            if (!dc_isar_feature(aa32_simdfmac, s)) {
                 return 1;
             }
             break;