target/arm: Implement FCVT (scalar, fixed-point) for fp16

Cc: qemu-stable@nongnu.org
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NRichard Henderson <richard.henderson@linaro.org>
Tested-by: NAlex Bennée <alex.bennee@linaro.org>
Message-id: 20180512003217.9105-5-richard.henderson@linaro.org
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target/arm/translate-a64.c

@@ -5697,8 +5697,21 @@ static void disas_fp_fixed_conv(DisasContext *s, uint32_t insn)
     bool sf = extract32(insn, 31, 1);
     bool itof;
 
-    if (sbit || (type > 1)
-        || (!sf && scale < 32)) {
+    if (sbit || (!sf && scale < 32)) {
+        unallocated_encoding(s);
+        return;
+    }
+
+    switch (type) {
+    case 0: /* float32 */
+    case 1: /* float64 */
+        break;
+    case 3: /* float16 */
+        if (arm_dc_feature(s, ARM_FEATURE_V8_FP16)) {
+            break;
+        }
+        /* fallthru */
+    default:
         unallocated_encoding(s);
         return;
     }