target/arm: Implement VFP fp16 VMOV between gp and halfprec registers

Implement the VFP fp16 variant of VMOV that transfers a 16-bit
value between a general purpose register and a VFP register.

Note that Rt == 15 is UNPREDICTABLE; since this insn is v8 and later
only we have no need to replicate the old "updates CPSR.NZCV"
behaviour that the singleprec version of this insn does.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200828183354.27913-22-peter.maydell@linaro.org

target/arm/translate-vfp.c.inc

@@ -809,6 +809,40 @@ static bool trans_VMSR_VMRS(DisasContext *s, arg_VMSR_VMRS *a)
     return true;
 }
 
+static bool trans_VMOV_half(DisasContext *s, arg_VMOV_single *a)
+{
+    TCGv_i32 tmp;
+
+    if (!dc_isar_feature(aa32_fp16_arith, s)) {
+        return false;
+    }
+
+    if (a->rt == 15) {
+        /* UNPREDICTABLE; we choose to UNDEF */
+        return false;
+    }
+
+    if (!vfp_access_check(s)) {
+        return true;
+    }
+
+    if (a->l) {
+        /* VFP to general purpose register */
+        tmp = tcg_temp_new_i32();
+        neon_load_reg32(tmp, a->vn);
+        tcg_gen_andi_i32(tmp, tmp, 0xffff);
+        store_reg(s, a->rt, tmp);
+    } else {
+        /* general purpose register to VFP */
+        tmp = load_reg(s, a->rt);
+        tcg_gen_andi_i32(tmp, tmp, 0xffff);
+        neon_store_reg32(tmp, a->vn);
+        tcg_temp_free_i32(tmp);
+    }
+
+    return true;
+}
+
 static bool trans_VMOV_single(DisasContext *s, arg_VMOV_single *a)
 {
     TCGv_i32 tmp;

target/arm/vfp.decode

@@ -74,6 +74,7 @@ VDUP         ---- 1110 1 b:1 q:1 0 .... rt:4 1011 . 0 e:1 1 0000 \
              vn=%vn_dp
 
 VMSR_VMRS    ---- 1110 111 l:1 reg:4 rt:4 1010 0001 0000
+VMOV_half    ---- 1110 000 l:1 .... rt:4 1001 . 001 0000    vn=%vn_sp
 VMOV_single  ---- 1110 000 l:1 .... rt:4 1010 . 001 0000    vn=%vn_sp
 
 VMOV_64_sp   ---- 1100 010 op:1 rt2:4 rt:4 1010 00.1 ....   vm=%vm_sp