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?
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;
+}
