On Tue, 16 Jul 2019, Jan Hubicka wrote:
> Hi,
> this is the hunk we omitted from the original patch enabling TBAA for
> ODR types. Currently record_component_aliases record all pointers as
> void *. This is because canonical type merging handles them this way
> and thus it may merge for example
>
> strut a { int *ptr;};
>
> and
>
> struct b { short *ptr;};
>
> into one canonical type. The alias set of that canonical type then must
> conflict with both int * and short * which we do by globing it to void *
> which conflict with everything.
>
> For ODR types where we do canonical types based on their name we however
> assign differnt TYPE_CANONICAL to each of them. Thanks to this we can
> make alias set to contain int * or short * respectively.
>
>
> Bootstrapped/regtested x86_64-linux, OK?
OK.
Richard.
> Honza
> * alias.c (record_component_aliases): Do not simplify pointed-to
> types of ODR types
> * testsuite/g++.dg/lto/alias-4_0.C
> Index: alias.c
> ===================================================================
> --- alias.c (revision 273478)
> +++ alias.c (working copy)
> @@ -1202,47 +1202,52 @@ record_component_aliases (tree type)
> case RECORD_TYPE:
> case UNION_TYPE:
> case QUAL_UNION_TYPE:
> - for (field = TYPE_FIELDS (type); field != 0; field = DECL_CHAIN
> (field))
> - if (TREE_CODE (field) == FIELD_DECL && !DECL_NONADDRESSABLE_P (field))
> - {
> - /* LTO type merging does not make any difference between
> - component pointer types. We may have
> -
> - struct foo {int *a;};
> -
> - as TYPE_CANONICAL of
> -
> - struct bar {float *a;};
> -
> - Because accesses to int * and float * do not alias, we would get
> - false negative when accessing the same memory location by
> - float ** and bar *. We thus record the canonical type as:
> -
> - struct {void *a;};
> -
> - void * is special cased and works as a universal pointer type.
> - Accesses to it conflicts with accesses to any other pointer
> - type. */
> - tree t = TREE_TYPE (field);
> - if (in_lto_p)
> - {
> - /* VECTOR_TYPE and ARRAY_TYPE share the alias set with their
> - element type and that type has to be normalized to void *,
> - too, in the case it is a pointer. */
> - while (!canonical_type_used_p (t) && !POINTER_TYPE_P (t))
> - {
> - gcc_checking_assert (TYPE_STRUCTURAL_EQUALITY_P (t));
> - t = TREE_TYPE (t);
> - }
> - if (POINTER_TYPE_P (t))
> - t = ptr_type_node;
> - else if (flag_checking)
> - gcc_checking_assert (get_alias_set (t)
> - == get_alias_set (TREE_TYPE (field)));
> - }
> -
> - record_alias_subset (superset, get_alias_set (t));
> - }
> + {
> + /* LTO non-ODR type merging does not make any difference between
> + component pointer types. We may have
> +
> + struct foo {int *a;};
> +
> + as TYPE_CANONICAL of
> +
> + struct bar {float *a;};
> +
> + Because accesses to int * and float * do not alias, we would get
> + false negative when accessing the same memory location by
> + float ** and bar *. We thus record the canonical type as:
> +
> + struct {void *a;};
> +
> + void * is special cased and works as a universal pointer type.
> + Accesses to it conflicts with accesses to any other pointer
> + type. */
> + bool void_pointers = in_lto_p
> + && (!odr_type_p (type)
> + || !odr_based_tbaa_p (type));
> + for (field = TYPE_FIELDS (type); field != 0; field = DECL_CHAIN (field))
> + if (TREE_CODE (field) == FIELD_DECL && !DECL_NONADDRESSABLE_P (field))
> + {
> + tree t = TREE_TYPE (field);
> + if (void_pointers)
> + {
> + /* VECTOR_TYPE and ARRAY_TYPE share the alias set with their
> + element type and that type has to be normalized to void *,
> + too, in the case it is a pointer. */
> + while (!canonical_type_used_p (t) && !POINTER_TYPE_P (t))
> + {
> + gcc_checking_assert (TYPE_STRUCTURAL_EQUALITY_P (t));
> + t = TREE_TYPE (t);
> + }
> + if (POINTER_TYPE_P (t))
> + t = ptr_type_node;
> + else if (flag_checking)
> + gcc_checking_assert (get_alias_set (t)
> + == get_alias_set (TREE_TYPE (field)));
> + }
> +
> + record_alias_subset (superset, get_alias_set (t));
> + }
> + }
> break;
>
> case COMPLEX_TYPE:
>
> Index: testsuite/g++.dg/lto/alias-4_0.C
> ===================================================================
> --- testsuite/g++.dg/lto/alias-4_0.C (nonexistent)
> +++ testsuite/g++.dg/lto/alias-4_0.C (working copy)
> @@ -0,0 +1,31 @@
> +/* { dg-lto-do run } */
> +/* { dg-lto-options { { -O3 -flto -fno-early-inlining } } } */
> +__attribute__ ((used))
> +short *ptr_init, **ptr=&ptr_init;
> +
> +__attribute__ ((used))
> +struct a {
> + int *aptr;
> +} a, *aptr=&a;
> +
> +void
> +write_ptr ()
> +{
> + *aptr = a;
> +}
> +
> +__attribute__ ((used))
> +void
> +test ()
> +{
> + *ptr = (short int *)0;
> + write_ptr ();
> + if (!__builtin_constant_p (*ptr == (void *)0))
> + __builtin_abort ();
> +}
> +int
> +main()
> +{
> + test ();
> + return 0;
> +}
>
--
Richard Biener <rguent...@suse.de>
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany;
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah; HRB 21284 (AG Nürnberg)
