[REPOST] Invalid Code when reading from unaligned zero-sized array

[Richard Biener]

Eric Botcazou <ebotcazou@adacore.com> wrote:
>> It's not fully fixing the issue as _all_ aggregates that may be
>> accessed beyond their declarations size are broken.
>
>Sure, but we don't need to support such nonsense in the general case. 
>And not 
>every language allows it, for example in Ada you cannot do that of
>course.

Well, we certainly need to support it as far as not ICEing

>> I'd say we should simply stop giving aggregates a mode besides
>BLKmode. 
>> What can possibly break with that ...
>
>Nothing, but this will unnecessarily pessimize well-behaved languages,
>e.g. in 
>Ada we overalign structures in some cases to give them integral modes.

What are the transformations that are enabled by making something not BLKmode?

On the gimple level I cannot think of one..

>> struct { char c[4]; }
>> 
>> has SImode, we accept all trailing arrays as possibly extending
>beyond the
>> struct declaration.
>>
>> Alternatively all structs with aggregate members should not have a
>> mode != BLKmode.
>
>This could work as well, although I'd restrict this to arrays,
>recursively.

Works for me.

Thanks,
Richard.