Re: Fix lto-symtab ICE during Ada LTO bootstrap

[Eric Botcazou <ebotcazou@adacore.com>]

> this patch fixes an ICE seen with Ada LTO bootstrap in reporting type
> mismatches and it also makes us to stop complaining about C++ ODR
> violation.  The warnings are however correct.  I looked at few:
> 
> ../../libiberty/xstrerror.c:40:14: warning: type of �strerror� does not
> match original declaration [-Wlto-type-mismatch] extern char *strerror
> (int);
>               ^
> 
> ../../gcc/ada/s-os_lib.adb:1007:16: note: return value type mismatch
>        function strerror (errnum : Integer) return System.Address;
>                 ^
> 
> ../../gcc/ada/s-os_lib.adb:1007:16: note:
> �system__os_lib__errno_message__strerror� was previously declared here
> 
> Here we have function returning pointer WRT function returning integer:

This one is on purpose and cannot be easily changed.  Pointer types (or access 
types as called in Ada) are avoided as much as possible in the runtime because 
they drag the accessibility machinery, which is the machinery present in the 
language to eliminate dangling references and is heavy; so they are usually 
imported as System.Address instead.

> <built-in>: warning: type of �__builtin_strlen� does not match original
> declaration [-Wlto-type-mismatch] ../../gcc/ada/osint.adb:422:19: note:
> return value type mismatch
> ../../gcc/ada/osint.adb:422:19: note: type �integer� should match type �long
> unsigned int�
> 
> Here the signedness of integer does not match:

Yes, it's clearly incorrect on the Ada side and should be fixed in osint.adb.

> ../../gcc/ada/s-os_lib.ads:1053:4: warning: type of
> �system__os_lib__directory_separator� does not match original declaration
> [-Wlto-type-mismatch] Directory_Separator : constant Character;
>     ^
> 
> ../../gcc/ada/adaint.c:225:6: note: type �char� should match type �volatile
> character� char __gnat_dir_separator = DIR_SEPARATOR;
>       ^
> 
> Here we get difference in  signedness and volatility:

The signedness issue for Character is known and we plan to address it; the 
volatility issue was overlooked but looks fixable too.

> All those types will lead to wrong code if ever written to same memory
> location because of TBAA.  Eric, does Ada need all this types to be TBAA
> compatible? If so, we need to implement more strict globbing as we did for
> Fortran and we probably finally need to make the globbing aware of
> languages involved (we definitly don't want to glob pointers and integers
> for C/C++ programs)

I think that we can fix all the problems on the Ada side except for the 
pointer/System.Address duality (which can be even more problematic on 
architectures that use different calling conventions for them).

> Eric, it would be great to have a stand alone testcases in style of
> gcc/testsuite/gfortran.dg/lto/bind_c-*
> which stores and reads the same memory location in same alias set and thus
> trigger the undefined behvaiour.

OK, I'll think about that, thanks.

-- 
Eric Botcazou