[PATCH v3] target/i386: Remove compilation errors when -Werror=maybe-uninitialized

[Eric Auger <eric.auger@redhat.com>]

To avoid compilation errors when -Werror=maybe-uninitialized is used,
add a default case with g_assert_not_reached().

Otherwise with GCC 11.3.1 "cc (GCC) 11.3.1 20220421 (Red Hat 11.3.1-2)"
we get:

../target/i386/ops_sse.h: In function ‘helper_vpermdq_ymm’:
../target/i386/ops_sse.h:2495:13: error: ‘r3’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]
     2495 |     d->Q(3) = r3;
          |     ~~~~~~~~^~~~
../target/i386/ops_sse.h:2494:13: error: ‘r2’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]
     2494 |     d->Q(2) = r2;
          |     ~~~~~~~~^~~~
../target/i386/ops_sse.h:2493:13: error: ‘r1’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]
     2493 |     d->Q(1) = r1;
          |     ~~~~~~~~^~~~
../target/i386/ops_sse.h:2492:13: error: ‘r0’ may be used
uninitialized in this function [-Werror=maybe-uninitialized]
     2492 |     d->Q(0) = r0;
          |     ~~~~~~~~^~~~

Signed-off-by: Eric Auger <eric.auger@redhat.com>

---
v2 -> v3:
- use g_assert_not_reached() and document the compiler in use
---
 target/i386/ops_sse.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/target/i386/ops_sse.h b/target/i386/ops_sse.h
index 3cbc36a59d..0bd6bfad8a 100644
--- a/target/i386/ops_sse.h
+++ b/target/i386/ops_sse.h
@@ -2470,6 +2470,8 @@ void helper_vpermdq_ymm(Reg *d, Reg *v, Reg *s, uint32_t order)
         r0 = s->Q(2);
         r1 = s->Q(3);
         break;
+    default: /* default case added to help the compiler to avoid warnings */
+        g_assert_not_reached();
     }
     switch ((order >> 4) & 3) {
     case 0:
@@ -2488,6 +2490,8 @@ void helper_vpermdq_ymm(Reg *d, Reg *v, Reg *s, uint32_t order)
         r2 = s->Q(2);
         r3 = s->Q(3);
         break;
+    default: /* default case added to help the compiler to avoid warnings */
+        g_assert_not_reached();
     }
     d->Q(0) = r0;
     d->Q(1) = r1;
-- 
2.37.3