target/arm: Implement MVE LCTP

Implement the MVE LCTP instruction.

We put its decode and implementation with the other
low-overhead-branch insns because although it is only present if MVE
is implemented it is logically in the same group as the other LOB
insns.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210614151007.4545-7-peter.maydell@linaro.org

target/arm/t32.decode

@@ -674,5 +674,7 @@ BL               1111 0. .......... 11.1 ............         @branch24
     DLS          1111 0 0000 100     rn:4 1110 0000 0000 0001
     WLS          1111 0 0000 100     rn:4 1100 . .......... 1 imm=%lob_imm
     LE           1111 0 0000 0 f:1 0 1111 1100 . .......... 1 imm=%lob_imm
+
+    LCTP         1111 0 0000 000     1111 1110 0000 0000 0001
   ]
 }

target/arm/translate.c

@@ -8191,6 +8191,30 @@ static bool trans_LE(DisasContext *s, arg_LE *a)
     return true;
 }
 
+static bool trans_LCTP(DisasContext *s, arg_LCTP *a)
+{
+    /*
+     * M-profile Loop Clear with Tail Predication. Since our implementation
+     * doesn't cache branch information, all we need to do is reset
+     * FPSCR.LTPSIZE to 4.
+     */
+    TCGv_i32 ltpsize;
+
+    if (!dc_isar_feature(aa32_lob, s) ||
+        !dc_isar_feature(aa32_mve, s)) {
+        return false;
+    }
+
+    if (!vfp_access_check(s)) {
+        return true;
+    }
+
+    ltpsize = tcg_const_i32(4);
+    store_cpu_field(ltpsize, v7m.ltpsize);
+    return true;
+}
+
+
 static bool op_tbranch(DisasContext *s, arg_tbranch *a, bool half)
 {
     TCGv_i32 addr, tmp;