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

From-SVN: r246212
This commit is contained in:
Jason Merrill 2017-03-16 17:16:45 -04:00 committed by Jason Merrill
parent 85e653c925
commit 2e92d7ada9
3 changed files with 39 additions and 0 deletions
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2
gcc/cp/ChangeLog
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@ -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.

6
gcc/cp/decl.c
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@ -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,

31
gcc/testsuite/g++.dg/cpp1z/byte1.C Normal file
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@ -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();
}