Re: Teach same_types_for_tbaa to structurally compare arrays, pointers and vectors

[Richard Biener <rguenther@suse.de>]

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On Wed, 29 May 2019, Jan Hubicka wrote:

> > On Mon, 27 May 2019, Jan Hubicka wrote:
> > 
> > > Hi,
> > > this is minimal version of patch adding just the pointer compare.
> > > Bootstrapped/regtested x86_64-linux, makes sense? :)
> > 
> > Yes, obviously.
> 
> Thanks, i will go ahead with installing it.
> Note that I have also tested removal of:
> 
>   /* ??? Array types are not properly unified in all cases as we have
>      spurious changes in the index types for example.  Removing this
>      causes all sorts of problems with the Fortran frontend.  */
>   if (TREE_CODE (type1) == ARRAY_TYPE
>       && TREE_CODE (type2) == ARRAY_TYPE)
>     return -1;
> 
> And it causes no regressions.  I looked for the history and see you
> added it in 2009 because Fortran mixes up array of chars with char
> itself.  I am not sure if that was fixed since then or it is just
> about missing testcase?

I think we had a testcase back then and I'm not aware of any fixes
here.  The introducing mail says we miscompile protein (part of
polyhedron).  Another thing about arrays is that unification
doesn't work for VLAs even in C (consider nested fns being
inlined and sharing an array type with the caller), so we cannot
really say ARRAY_TYPEs with non-constant bounds are ever
"not equal".  So simply dropping this check looks wrong.
I'm not sure about char[] vs char but the FE definitely can
end up with char vs. char[1] and we need not consider those
different.

The fortran FE is similarly sloppy in other areas, see

      /* ??? We cannot simply use the type of operand #0 of the refs here
         as the Fortran compiler smuggles type punning into COMPONENT_REFs
         for common blocks instead of using unions like everyone else.  */
      tree type1 = DECL_CONTEXT (field1);
      tree type2 = DECL_CONTEXT (field2);



> It does not seem to be that important, but looks odd 
> and makes me woried about other changes :)
> 
> Honza
> > 
> > Richard.
> 

-- 
Richard Biener <rguenther@suse.de>
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