[Bug middle-end/59711] ICE in force_constant_size, at gimplify.c:619 with variably-modified return type

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59711

--- Comment #5 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> I believe this isn't fixable with the GIMPLE IL as-is - without lowering
> to the fact that g () returns by storing to a return slot.  Not sure why
> 3.4 ICEd (2.95.2 also ICEs btw ...).

Because historically you cannot create temporaries with variable size in GCC.

> Well, maybe we can fix it if we allow creating of a variable-size temporary
> during gimplification.  That is, the gimple code needs to look like
> 
>   tem = WITH_SIZE_EXPR <g (), sizeof (S)>;
>   return tem.a[0];
> 
> which of course then has the issue that we can't have WITH_SIZE_EXPR around
> calls.  Thus really the only way is to lower the return slot fact early.
> 
>   g (&tem);
>   return tem.a[0];

Of course this situation occurs very frequently in Ada and we explicitly create
the temporary in gigi.