target/arm: Implement MVE DLSTP

Implement the MVE DLSTP insn; this is like the existing DLS
insn, except that it must do an FPU access check and it
sets LTPSIZE to the value specified in the insn.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210614151007.4545-9-peter.maydell@linaro.org

2 files changed, 27 insertions, 5 deletions

diff --git a/target/arm/t32.decode b/target/arm/t32.decode
index 6906829265..1b75db5065 100644
--- a/target/arm/t32.decode
+++ b/target/arm/t32.decode
@@ -671,14 +671,17 @@ BL               1111 0. .......... 11.1 ............         @branch24
     # LE and WLS immediate
     %lob_imm 1:10 11:1 !function=times_2
 
-    DLS          1111 0 0000 100     rn:4 1110 0000 0000 0001
+    DLS          1111 0 0000 100     rn:4 1110 0000 0000 0001 size=4
     WLS          1111 0 0000 100     rn:4 1100 . .......... 1 imm=%lob_imm size=4
     {
       LE         1111 0 0000 0 f:1 0 1111 1100 . .......... 1 imm=%lob_imm
       # This is WLSTP
       WLS        1111 0 0000 0 size:2 rn:4 1100 . .......... 1 imm=%lob_imm
     }
-
-    LCTP         1111 0 0000 000     1111 1110 0000 0000 0001
+    {
+      LCTP       1111 0 0000 000     1111 1110 0000 0000 0001
+      # This is DLSTP
+      DLS        1111 0 0000 0 size:2 rn:4 1110 0000 0000 0001
+    }
   ]
 }
diff --git a/target/arm/translate.c b/target/arm/translate.c
index 78878e9b19..1ad0e61fac 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -8114,13 +8114,32 @@ static bool trans_DLS(DisasContext *s, arg_DLS *a)
         return false;
     }
     if (a->rn == 13 || a->rn == 15) {
-        /* CONSTRAINED UNPREDICTABLE: we choose to UNDEF */
+        /*
+         * For DLSTP rn == 15 is a related encoding (LCTP); the
+         * other cases caught by this condition are all
+         * CONSTRAINED UNPREDICTABLE: we choose to UNDEF
+         */
         return false;
     }
 
-    /* Not a while loop, no tail predication: just set LR to the count */
+    if (a->size != 4) {
+        /* DLSTP */
+        if (!dc_isar_feature(aa32_mve, s)) {
+            return false;
+        }
+        if (!vfp_access_check(s)) {
+            return true;
+        }
+    }
+
+    /* Not a while loop: set LR to the count, and set LTPSIZE for DLSTP */
     tmp = load_reg(s, a->rn);
     store_reg(s, 14, tmp);
+    if (a->size != 4) {
+        /* DLSTP: set FPSCR.LTPSIZE */
+        tmp = tcg_const_i32(a->size);
+        store_cpu_field(tmp, v7m.ltpsize);
+    }
     return true;
 }