Re: [PATCH v2] target/i386: Remove compilation errors when -Werror=maybe-uninitialized

[Philippe Mathieu-Daudé]

On 22/12/22 09:18, Paolo Bonzini wrote:
> On 12/21/22 17:36, Eric Auger wrote:
> > To avoid compilation errors when -Werror=maybe-uninitialized is used,
> > replace 'case 3' by 'default'.
> >
> > Otherwise 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;
> >          |     ~~~~~~~~^~~~

With what compiler? Is that a supported one?

> > Signed-off-by: Eric Auger <eric.auger@redhat.com>
> > Suggested-by: Stefan Weil <sw@weilnetz.de>
> > Fixes: 790684776861 ("target/i386: reimplement 0x0f 0x3a, add AVX")
> > ---
> >   target/i386/ops_sse.h | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/target/i386/ops_sse.h b/target/i386/ops_sse.h
> > index 3cbc36a59d..c442c8c10c 100644
> > --- a/target/i386/ops_sse.h
> > +++ b/target/i386/ops_sse.h
> > @@ -2466,7 +2466,7 @@ void helper_vpermdq_ymm(Reg *d, Reg *v, Reg *s, 
> > uint32_t order)
> >           r0 = s->Q(0);
> >           r1 = s->Q(1);
> >           break;
> > -    case 3:
> > +    default:
> >           r0 = s->Q(2);
> >           r1 = s->Q(3);
> >           break;
> > @@ -2484,7 +2484,7 @@ void helper_vpermdq_ymm(Reg *d, Reg *v, Reg *s, 
> > uint32_t order)
> >           r2 = s->Q(0);
> >           r3 = s->Q(1);
> >           break;
> > -    case 3:
> > +    default:
> >           r2 = s->Q(2);
> >           r3 = s->Q(3);
> >           break;
>
> Queued, but this compiler sucks. :)

Can't we simply add a dumb 'default' case? So when reviewing we don't
have to evaluate 'default' means 3 here.

-- >8 --
--- 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:
+        qemu_build_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:
+        qemu_build_not_reached();
     }
     d->Q(0) = r0;
     d->Q(1) = r1;
---