* decl.c (start_enum): std::byte aliases anything.

From-SVN: r246212

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 99836fbaeea83511c77de6a15f8db7050562f4cc..089d388dd4d20957f950c8a765e137c7aa7bb0b5 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,7 @@
 2017-03-16  Jason Merrill  <jason@redhat.com>
 
+       * decl.c (start_enum): std::byte aliases anything.
+
        PR c++/79797
        * constexpr.c (lookup_placeholder): Tweak.
 

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 0ecd30b691b08badc06f109b63aff0acb318f313..61ecf81b27ae82724adbccbfd9724df1ba65a92d 100644 (file)
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -14079,6 +14079,12 @@ start_enum (tree name, tree enumtype, tree underlying_type,
        {
          enumtype = cxx_make_type (ENUMERAL_TYPE);
          enumtype = pushtag (name, enumtype, /*tag_scope=*/ts_current);
+
+         /* std::byte aliases anything.  */
+         if (enumtype != error_mark_node
+             && TYPE_CONTEXT (enumtype) == std_node
+             && !strcmp ("byte", TYPE_NAME_STRING (enumtype)))
+           TYPE_ALIAS_SET (enumtype) = 0;
        }
       else
          enumtype = xref_tag (enum_type, name, /*tag_scope=*/ts_current,

diff --git a/gcc/testsuite/g++.dg/cpp1z/byte1.C b/gcc/testsuite/g++.dg/cpp1z/byte1.C
new file mode 100644 (file)
index 0000000..51c1a33
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/byte1.C
@@ -0,0 +1,31 @@
+// Test for std::byte aliasing properties.
+// { dg-options "-std=c++1z -O3" }
+
+#include <cstddef>
+
+using byte = std::byte;
+
+enum class notbyte: unsigned char {} *np;
+
+int main()
+{
+  int x;
+
+  /* Stores through byte* can alias int, so the compiler can't optimize
+     "x != 0".  */
+  byte *p = (byte*)&x;
+  x = 42;
+  for (int i = 0; i < 4; ++i)
+    p[i] = byte(0);
+  if (x != 0)
+    __builtin_abort();
+
+  /* Stores through notbyte* mustn't alias int, so at -O3 the compiler should
+     optimize "x != 42" to false.  */
+  notbyte *np = (notbyte*)&x; 
+  x = 42;
+  for (int i = 0; i < 4; ++i)
+    np[i] = notbyte(0);
+  if (x != 42)
+    __builtin_abort();
+}