Re: Fix verify_type ICE with -fshort-enum

[Richard Biener <richard.guenther@gmail.com>]

On Wed, Jun 17, 2015 at 12:10 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>> >>       PR middle-end/66325
>> >>       * c-decl.c (start_enum): Set TYPE_PACKED consistently among type variants.
>> >> Index: c-decl.c
>> >> ===================================================================
>> >> --- c-decl.c  (revision 224250)
>> >> +++ c-decl.c  (working copy)
>> >> @@ -7946,7 +7946,8 @@
>> >>    the_enum->enum_overflow = 0;
>> >>
>> >>    if (flag_short_enums)
>> >> -    TYPE_PACKED (enumtype) = 1;
>> >> +    for (tree v = TYPE_MAIN_VARIANT (enumtype); v ;v = TYPE_NEXT_VARIANT (v))
>>
>> Though I wonder why flag_short_enums was not true when building the
>> (main-)variant?
>
> What I believe happens is that there is forward declaration of enum that leads
> to biuld incomplete enum type that has no packed flag set.  Then we produce
> a type variant and after that we complete the main variant, but do not update
> the other variant.
>
> Actually looking into where the variant is updated, it happens in finish_enum
> that copies many flags, perhaps it would make more sense to copy TYPE_PACKED
> there?

Yes, it sounds like so.

>> Looks like -fshort-enums is also 'Optimization', so the above is bogus for
>>
>> enum foo {x = 1 };
>>
>> void __attribute__((optimize(short-enums))) foo()
>> {
>>   const enum foo x = 1;
>> }
>>
>> no?  The main variant is correctly _not_ packed but now you make it
>> packed as you reach foo ()?
>
> Perhaps it is defined as Optimization but it does not bind to uses of types:
>
> enum foo {a,b,c};
>  __attribute__((optimize("short-enums")))
> main()
> {
>   const enum foo x;
>   enum bar {a,b,c};
>   printf ("%i %i\n",sizeof (x), sizeof(enum bar));
> }
>
> prints
> 4 1
>
> it depends when the main variant is finished.  I wonder if there is any
> practical value on support Optimization attribute for this kind of ABI breaking
> options.  It may be easier to simply drop the Optimization flag completely from
> -fshort-enums and friends.
>
> -fshort-double ICEs at initialization time at least since 4.8.x
> $ gcc t.c -fshort-double
> <built-in>: internal compiler error: in layout_type, at stor-layout.c:2220
> 0xafe41b layout_type(tree_node*)
>         ../../gcc/stor-layout.c:2219
>
> so I suggest dropping that flag completely.

IIRC it "works" for -m32, but yes...

Yes also to _not_ make ABI changing flags 'Optimization'.

Richard.

> Honza
>>
>> Richard.
>>
>> > Please fix the formatting here: no space before ;.
>> >
>> > Ok with that change.
>> >
>> >         Marek