Re: Fix false -Wodr warnings

[Richard Biener <richard.guenther@gmail.com>]

On Sun, Apr 14, 2019 at 10:59 PM Jan Hubicka <hubicka@ucw.cz> wrote:
>
> Hi,
> this patch fixes false warning that is output when different -std
> settings are used. In this case C++ FE produces same declaration in
> different representations which differ by 0 sized fileds only.
> The patch makes them to be ignored (and I checked we ignore them for
> canonical type merging too)
>
> Bootstrapped/regtested x86_64-linux, comitted.

The testcase is bogus

WARNING: lto.exp does not support dg-do
WARNING: lto.exp does not support dg-options in primary source file


> Honza
>
>         PR lto/89358
>         * g++.dg/lto/pr89358_0.C: New testcase.
>         * g++.dg/lto/pr89358_1.C: New testcase.
>         * ipa-devirt.c (skip_in_fields_list_p): New.
>         (odr_types_equivalent_p): Use it.
> Index: testsuite/g++.dg/lto/pr89358_0.C
> ===================================================================
> --- testsuite/g++.dg/lto/pr89358_0.C    (nonexistent)
> +++ testsuite/g++.dg/lto/pr89358_0.C    (working copy)
> @@ -0,0 +1,11 @@
> +/* { dg-do link } */
> +/* { dg-options "-std=c++17"  } */
> +#include <map>
> +
> +extern void test();
> +
> +int main()
> +{
> +        std::map<int, int> m;
> +        test();
> +}
> Index: testsuite/g++.dg/lto/pr89358_1.C
> ===================================================================
> --- testsuite/g++.dg/lto/pr89358_1.C    (nonexistent)
> +++ testsuite/g++.dg/lto/pr89358_1.C    (working copy)
> @@ -0,0 +1,7 @@
> +/* { dg-options "-std=c++14"  } */
> +#include <map>
> +
> +void test()
> +{
> +        std::map<int, int> m;
> +}
> Index: ipa-devirt.c
> ===================================================================
> --- ipa-devirt.c        (revision 270324)
> +++ ipa-devirt.c        (working copy)
> @@ -1282,6 +1282,24 @@ warn_types_mismatch (tree t1, tree t2, l
>      inform (loc_t2, "the incompatible type is defined here");
>  }
>
> +/* Return true if T should be ignored in TYPE_FIELDS for ODR comparsion.  */
> +
> +static bool
> +skip_in_fields_list_p (tree t)
> +{
> +  if (TREE_CODE (t) != FIELD_DECL)
> +    return true;
> +  /* C++ FE introduces zero sized fields depending on -std setting, see
> +     PR89358.  */
> +  if (DECL_SIZE (t)
> +      && integer_zerop (DECL_SIZE (t))
> +      && DECL_ARTIFICIAL (t)
> +      && DECL_IGNORED_P (t)
> +      && !DECL_NAME (t))
> +    return true;
> +  return false;
> +}
> +
>  /* Compare T1 and T2, report ODR violations if WARN is true and set
>     WARNED to true if anything is reported.  Return true if types match.
>     If true is returned, the types are also compatible in the sense of
> @@ -1548,9 +1566,9 @@ odr_types_equivalent_p (tree t1, tree t2
>                  f1 = TREE_CHAIN (f1), f2 = TREE_CHAIN (f2))
>               {
>                 /* Skip non-fields.  */
> -               while (f1 && TREE_CODE (f1) != FIELD_DECL)
> +               while (f1 && skip_in_fields_list_p (f1))
>                   f1 = TREE_CHAIN (f1);
> -               while (f2 && TREE_CODE (f2) != FIELD_DECL)
> +               while (f2 && skip_in_fields_list_p (f2))
>                   f2 = TREE_CHAIN (f2);
>                 if (!f1 || !f2)
>                   break;