This marks structures which include a byte array
as typeless storage.
Bootstrapped and regression tested on x86_64.
c: Add support for byte arrays in C2Y
To get correct aliasing behavior requires that structures and unions
that contain a byte array, i.e. an array of non-atomic character
type (N3254), are marked with TYPE_TYPELESS_STORAGE.
gcc/c/
* c-decl.cc (grokdeclarator, finish_struct): Set and
propagate TYPE_TYPELESS_STORAGE.
gcc/testsuite/
* gcc.dg/c2y-byte-alias-1.c: New test.
* gcc.dg/c2y-byte-alias-2.c: New test.
* gcc.dg/c2y-byte-alias-3.c: New test.
diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 0eac266471f..65561f3cbcc 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -7499,12 +7499,17 @@ grokdeclarator (const struct c_declarator *declarator,
modify the shared type, so we gcc_assert (itype)
below. */
{
+ bool typeless = flag_isoc2y
+ && ((char_type_p (type)
+ && !(type_quals & TYPE_QUAL_ATOMIC))
+ || (AGGREGATE_TYPE_P (type)
+ && TYPE_TYPELESS_STORAGE (type)));
+
addr_space_t as = DECODE_QUAL_ADDR_SPACE (type_quals);
if (!ADDR_SPACE_GENERIC_P (as) && as != TYPE_ADDR_SPACE (type))
type = build_qualified_type (type,
ENCODE_QUAL_ADDR_SPACE (as));
-
- type = build_array_type (type, itype);
+ type = build_array_type (type, itype, typeless);
}
if (type != error_mark_node)
@@ -9656,6 +9661,10 @@ finish_struct (location_t loc, tree t, tree fieldlist,
tree attributes,
if (DECL_NAME (x)
|| RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
saw_named_field = true;
+
+ if (AGGREGATE_TYPE_P (TREE_TYPE (x))
+ && TYPE_TYPELESS_STORAGE (TREE_TYPE (x)))
+ TYPE_TYPELESS_STORAGE (t) = true;
}
detect_field_duplicates (fieldlist);
@@ -9856,6 +9865,7 @@ finish_struct (location_t loc, tree t, tree fieldlist,
tree attributes,
TYPE_FIELDS (x) = TYPE_FIELDS (t);
TYPE_LANG_SPECIFIC (x) = TYPE_LANG_SPECIFIC (t);
TYPE_TRANSPARENT_AGGR (x) = TYPE_TRANSPARENT_AGGR (t);
+ TYPE_TYPELESS_STORAGE (x) = TYPE_TYPELESS_STORAGE (t);
C_TYPE_FIELDS_READONLY (x) = C_TYPE_FIELDS_READONLY (t);
C_TYPE_FIELDS_VOLATILE (x) = C_TYPE_FIELDS_VOLATILE (t);
C_TYPE_FIELDS_NON_CONSTEXPR (x) = C_TYPE_FIELDS_NON_CONSTEXPR (t);
diff --git a/gcc/testsuite/gcc.dg/c2y-byte-alias-1.c
b/gcc/testsuite/gcc.dg/c2y-byte-alias-1.c
new file mode 100644
index 00000000000..30bc2c09c2f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c2y-byte-alias-1.c
@@ -0,0 +1,46 @@
+/* { dg-do run } */
+/* { dg-options "-std=c2y -O2" } */
+
+struct f { _Alignas(int) char buf[sizeof(int)]; };
+struct f2 { struct f x; };
+union g { _Alignas(int) char buf[sizeof(int)]; };
+
+[[gnu::noinline]]
+int foo(struct f *p, int *q)
+{
+ *q = 1;
+ *p = (struct f){ };
+ return *q;
+}
+
+[[gnu::noinline]]
+int foo2(struct f2 *p, int *q)
+{
+ *q = 1;
+ *p = (struct f2){ };
+ return *q;
+}
+
+[[gnu::noinline]]
+int bar(union g *p, int *q)
+{
+ *q = 1;
+ *p = (union g){ };
+ return *q;
+}
+
+
+int main()
+{
+ struct f p;
+ if (0 != foo(&p, (void*)&p.buf))
+ __builtin_abort();
+
+ struct f2 p2;
+ if (0 != foo2(&p2, (void*)&p2.x.buf))
+ __builtin_abort();
+
+ union g q;
+ if (0 != bar(&q, (void*)&q.buf))
+ __builtin_abort();
+}
diff --git a/gcc/testsuite/gcc.dg/c2y-byte-alias-2.c
b/gcc/testsuite/gcc.dg/c2y-byte-alias-2.c
new file mode 100644
index 00000000000..9bd2d18b386
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c2y-byte-alias-2.c
@@ -0,0 +1,43 @@
+/* { dg-do run } */
+/* { dg-options "-std=c2y -O2" } */
+
+struct f2 {
+ struct f {
+ _Alignas(int) char buf[sizeof(int)];
+ } x[2];
+ int i;
+};
+
+[[gnu::noinline]]
+int foo2(struct f2 *p, int *q)
+{
+ *q = 1;
+ *p = (struct f2){ };
+ return *q;
+}
+
+struct g2 {
+ union g {
+ _Alignas(int) char buf[sizeof(int)];
+ } x[2];
+ int i;
+};
+
+[[gnu::noinline]]
+int bar2(struct g2 *p, int *q)
+{
+ *q = 1;
+ *p = (struct g2){ };
+ return *q;
+}
+
+int main()
+{
+ struct f2 p2;
+ if (0 != foo2(&p2, (void*)&p2.x[0].buf))
+ __builtin_abort();
+
+ struct g2 q2;
+ if (0 != bar2(&q2, (void*)&q2.x[0].buf))
+ __builtin_abort();
+}
diff --git a/gcc/testsuite/gcc.dg/c2y-byte-alias-3.c
b/gcc/testsuite/gcc.dg/c2y-byte-alias-3.c
new file mode 100644
index 00000000000..f88eab2e92f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/c2y-byte-alias-3.c
@@ -0,0 +1,47 @@
+/* { dg-do run } */
+/* { dg-options "-std=c2y -O2" } */
+
+struct f { _Alignas(int) typeof(volatile char) buf[sizeof(int)]; };
+struct f2 { struct f x; };
+union g { _Alignas(int) volatile char buf[sizeof(int)]; };
+
+
+[[gnu::noinline]]
+int foo(struct f *p, int *q)
+{
+ *q = 1;
+ *p = (struct f){ };
+ return *q;
+}
+
+[[gnu::noinline]]
+int foo2(struct f2 *p, int *q)
+{
+ *q = 1;
+ *p = (struct f2){ };
+ return *q;
+}
+
+[[gnu::noinline]]
+int bar(union g *p, int *q)
+{
+ *q = 1;
+ *p = (union g){ };
+ return *q;
+}
+
+
+int main()
+{
+ struct f p;
+ if (0 != foo(&p, (void*)&p.buf))
+ __builtin_abort();
+
+ struct f2 p2;
+ if (0 != foo2(&p2, (void*)&p2.x.buf))
+ __builtin_abort();
+
+ union g q;
+ if (0 != bar(&q, (void*)&q.buf))
+ __builtin_abort();
+}
