@@ -9749,7 +9749,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
C_TYPE_BEING_DEFINED (t) = 0;
/* Set type canonical based on equivalence class. */
- if (flag_isoc23)
+ if (flag_isoc23 && !C_TYPE_VARIABLE_SIZE (t))
{
if (c_struct_htab == NULL)
c_struct_htab = hash_table<c_struct_hasher>::create_ggc (61);
@@ -420,11 +420,6 @@ c_var_mod_p (tree x, tree fn ATTRIBUTE_UNUSED)
alias_set_type
c_get_alias_set (tree t)
{
- /* Structs with variable size can alias different incompatible
- structs. Let them alias anything. */
- if (RECORD_OR_UNION_TYPE_P (t) && C_TYPE_VARIABLE_SIZE (t))
- return 0;
-
return c_common_get_alias_set (t);
}
@@ -1167,6 +1167,28 @@ common_type (tree t1, tree t2)
return c_common_type (t1, t2);
}
+
+
+/* Helper function for comptypes. For two compatible types, return 1
+ if they pass consistency checks. In particular we test that
+ TYPE_CANONICAL ist set correctly, i.e. the two types can alias. */
+
+static bool
+comptypes_verify (tree type1, tree type2)
+{
+ if (TYPE_CANONICAL (type1) != TYPE_CANONICAL (type2)
+ && !TYPE_STRUCTURAL_EQUALITY_P (type1)
+ && !TYPE_STRUCTURAL_EQUALITY_P (type2))
+ {
+ /* FIXME: check other types. */
+ if (RECORD_OR_UNION_TYPE_P (type1)
+ || TREE_CODE (type1) == ENUMERAL_TYPE
+ || TREE_CODE (type2) == ENUMERAL_TYPE)
+ return false;
+ }
+ return true;
+}
+
struct comptypes_data {
bool enum_and_int_p;
bool different_types_p;
@@ -1187,6 +1209,8 @@ comptypes (tree type1, tree type2)
struct comptypes_data data = { };
bool ret = comptypes_internal (type1, type2, &data);
+ gcc_checking_assert (!ret || comptypes_verify (type1, type2));
+
return ret ? (data.warning_needed ? 2 : 1) : 0;
}
@@ -1200,6 +1224,8 @@ comptypes_same_p (tree type1, tree type2)
struct comptypes_data data = { };
bool ret = comptypes_internal (type1, type2, &data);
+ gcc_checking_assert (!ret || comptypes_verify (type1, type2));
+
if (data.different_types_p)
return false;
@@ -1217,6 +1243,8 @@ comptypes_check_enum_int (tree type1, tree type2, bool *enum_and_int_p)
bool ret = comptypes_internal (type1, type2, &data);
*enum_and_int_p = data.enum_and_int_p;
+ gcc_checking_assert (!ret || comptypes_verify (type1, type2));
+
return ret ? (data.warning_needed ? 2 : 1) : 0;
}
@@ -1231,6 +1259,8 @@ comptypes_check_different_types (tree type1, tree type2,
bool ret = comptypes_internal (type1, type2, &data);
*different_types_p = data.different_types_p;
+ gcc_checking_assert (!ret || comptypes_verify (type1, type2));
+
return ret ? (data.warning_needed ? 2 : 1) : 0;
}
@@ -1245,6 +1275,10 @@ comptypes_equiv_p (tree type1, tree type2)
data.equiv = true;
bool ret = comptypes_internal (type1, type2, &data);
+ /* check that different equivance classes are assigned only
+ to types that are not compatible. */
+ gcc_checking_assert (ret || !comptypes (type1, type2));
+
return ret;
}
@@ -1593,9 +1627,6 @@ tagged_types_tu_compatible_p (const_tree t1, const_tree t2,
if (list_length (TYPE_FIELDS (t1)) != list_length (TYPE_FIELDS (t2)))
return false;
- if (data->equiv && (C_TYPE_VARIABLE_SIZE (t1) || C_TYPE_VARIABLE_SIZE (t2)))
- return false;
-
for (s1 = TYPE_FIELDS (t1), s2 = TYPE_FIELDS (t2);
s1 && s2;
s1 = DECL_CHAIN (s1), s2 = DECL_CHAIN (s2))
new file mode 100644
@@ -0,0 +1,24 @@
+/* { dg-do run } */
+/* { dg-options "-std=gnu23 -O2" } */
+
+typedef struct E { int a[2]; int b; } *A;
+
+void* foo(void* a, void *b, void *c, void *d)
+{
+ *(A**)a = c;
+
+ int N = 2;
+ typedef struct E { int a[N]; int b; } *B;
+ *(B**)b = d;
+
+ return *(A**)a;
+}
+
+int main()
+{
+ A *a, b, c;
+ if (&c != (A*)foo(&a, &a, &b, &c))
+ __builtin_abort();
+}
+
+
This is similar to the enum issue, where setting the alias set to zero is insufficient because also derived types need to be able to alias. After this change, it is also possible to add checking assertions that verify TYPE_CANONICAL for all tagged types at end of each call to the comptypes family. At least for the test suite this then shows no additional issues for tagged types. (We still make incorrect aliasing decisions at least for types derived from functions types (PR114959) but this is an ancient issue. We probably should set TYPE_CANONICAL in the FE similar to what is done for tagged types in C23.) Bootstrapped and regression tested on x86_64. C23: allow aliasing for types derived from structs with variable size Previously, we set the aliasing set of structures with variable size struct foo { int x[n]; char b; }; to zero. The reason is that such types can be compatible to diffrent structure types which are incompatible. struct foo { int x[2]; char b; }; struct foo { int x[3]; char b; }; But it is not enough to set the aliasing set to zero, because derived types would then still end up in different equivalence classes even though they might be compatible. Instead those types should be set to structural equivalency. We also add checking assertions that ensure that TYPE_CANONICAL is set correctly for all tagged types gcc/c/ * c-decl.cc (finish_struct): Do not set TYPE_CANONICAL for structure or unions with variable size. * c-objc-common.cc (c_get_alias_set): Do not set alias set to zero. * c-typeck.cc (comptypes_verify): New function. (comptypes,comptypes_same_p,comptypes_check_enum_int): Add assertion. (comptypes_equiv_p): Add assertion that ensures that compatible types have the same equivalence class. (tagged_types_tu_compatible_p): Remove now unneeded special case. gcc/testsuite/ * gcc.dg/gnu23-tag-alias-8.c: New test.