Silence false positive on LTO type merging waring

[Jan Hubicka]

> On Thu, 25 Jan 2018, Jan Hubicka wrote:
> 
> > Hi,
> > the testcase triggers invalid warning on type mismatch because array
> > of pointers to complete type has different alias set from array of pointers
> > to incomplete type.  This is valid, because incoplete pointer has alias set
> > of void_ptr which alias all pointers and arrays alias with their members.
> 
> But isn't that a problem?  Not if the pointer to incomlete type have
> alias set zero but IIRC they don't, right?

pointers to incomplete type are same as alias set of ptr_type_node (1 in this case)
and pointer to complete types have different alias set but that set has
is_pointer flag.  When checking for conflict we make 1 to alias with everything that
has is_pointer flag in it, so it will return true for these two array types.

Honza
> 
> Richard.
> 
> > I already silenced the wanring for pointers but I forgot about arrays.
> > 
> > Bootstrapped/regtested x86_64-linux, OK?
> > 	
> > 	* gcc.dg/lto/pr83954.h: New testcase.
> > 	* gcc.dg/lto/pr83954_0.c: New testcase.
> > 	* gcc.dg/lto/pr83954_1.c: New testcase.
> > 	* lto-symtab.c (warn_type_compatibility_p): Silence false positive
> > 	for type match warning on arrays of pointers.
> > 
> > Index: testsuite/gcc.dg/lto/pr83954.h
> > ===================================================================
> > --- testsuite/gcc.dg/lto/pr83954.h	(revision 0)
> > +++ testsuite/gcc.dg/lto/pr83954.h	(working copy)
> > @@ -0,0 +1,3 @@
> > +struct foo;
> > +extern struct foo *FOO_PTR_ARR[1];
> > +
> > Index: testsuite/gcc.dg/lto/pr83954_0.c
> > ===================================================================
> > --- testsuite/gcc.dg/lto/pr83954_0.c	(revision 0)
> > +++ testsuite/gcc.dg/lto/pr83954_0.c	(working copy)
> > @@ -0,0 +1,8 @@
> > +/* { dg-lto-do link } */
> > +#include "pr83954.h"
> > +
> > +int main() { 
> > +  // just to prevent symbol removal
> > +  FOO_PTR_ARR[1] = 0;
> > +  return 0;
> > +}
> > Index: testsuite/gcc.dg/lto/pr83954_1.c
> > ===================================================================
> > --- testsuite/gcc.dg/lto/pr83954_1.c	(revision 0)
> > +++ testsuite/gcc.dg/lto/pr83954_1.c	(working copy)
> > @@ -0,0 +1,7 @@
> > +#include "pr83954.h"
> > +
> > +struct foo {
> > + int x;
> > +};
> > +struct foo *FOO_PTR_ARR[1] = { 0 };
> > +
> > Index: lto/lto-symtab.c
> > ===================================================================
> > --- lto/lto-symtab.c	(revision 257009)
> > +++ lto/lto-symtab.c	(working copy)
> > @@ -284,11 +284,22 @@ warn_type_compatibility_p (tree prevaili
> >        alias_set_type set1 = get_alias_set (type);
> >        alias_set_type set2 = get_alias_set (prevailing_type);
> >  
> > -      if (set1 && set2 && set1 != set2 
> > -          && (!POINTER_TYPE_P (type) || !POINTER_TYPE_P (prevailing_type)
> > +      if (set1 && set2 && set1 != set2)
> > +	{
> > +          tree t1 = type, t2 = prevailing_type;
> > +
> > +	  /* Alias sets of arrays are the same as alias sets of the inner
> > +	     types.  */
> > +	  while (TREE_CODE (t1) == ARRAY_TYPE && TREE_CODE (t2) == ARRAY_TYPE)
> > +	    {
> > +	      t1 = TREE_TYPE (t1);
> > +	      t2 = TREE_TYPE (t2);
> > +	    }
> > +          if ((!POINTER_TYPE_P (t1) || !POINTER_TYPE_P (t2))
> >  	      || (set1 != TYPE_ALIAS_SET (ptr_type_node)
> > -		  && set2 != TYPE_ALIAS_SET (ptr_type_node))))
> > -        lev |= 5;
> > +		  && set2 != TYPE_ALIAS_SET (ptr_type_node)))
> > +             lev |= 5;
> > +	}
> >      }
> >  
> >    return lev;
> > 
> > 
> 
> -- 
> Richard Biener <rguenther@suse.de>
> SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)