target/loongarch: fix vldi/xvldi raise wrong error

on qemu we got an aborted error
**
ERROR:../target/loongarch/tcg/insn_trans/trans_vec.c.inc:3574:vldi_get_value: code should not be reached
Bail out! ERROR:../target/loongarch/tcg/insn_trans/trans_vec.c.inc:3574:vldi_get_value: code should not be reached
Aborted (core dumped)
but on 3A600/3A5000 we got a "Illegal instruction" error.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2971

Fixes: 29bb5d7 ("target/loongarch: Implement vldi")
 Cc: [email protected]
Reviewed-by: Bibo Mao <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Signed-off-by: Song Gao <[email protected]>
(cherry picked from commit c2a2e1ad2a749caa864281b1d4dc3f16c3f344f6)
Signed-off-by: Michael Tokarev <[email protected]>

Author: gaosong-loongson

target/loongarch/tcg/insn_trans/trans_vec.c.inc

@@ -3465,7 +3465,7 @@ TRANS(xvmsknz_b, LASX, gen_xx, gen_helper_vmsknz_b)
 static uint64_t vldi_get_value(DisasContext *ctx, uint32_t imm)
 {
     int mode;
-    uint64_t data, t;
+    uint64_t data = 0, t;
 
     /*
      * imm bit [11:8] is mode, mode value is 0-12.
@@ -3570,17 +3570,26 @@ static uint64_t vldi_get_value(DisasContext *ctx, uint32_t imm)
         }
         break;
     default:
-        generate_exception(ctx, EXCCODE_INE);
         g_assert_not_reached();
     }
     return data;
 }
 
+static bool check_valid_vldi_mode(arg_vldi *a)
+{
+   return  extract32(a->imm, 8, 4) <= 12;
+}
+
 static bool gen_vldi(DisasContext *ctx, arg_vldi *a, uint32_t oprsz)
 {
     int sel, vece;
     uint64_t value;
 
+    if (!check_valid_vldi_mode(a)) {
+        generate_exception(ctx, EXCCODE_INE);
+        return true;
+    }
+
     if (!check_vec(ctx, oprsz)) {
         return true;
     }