https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89624
Bug ID: 89624
Summary: HLE acquire/release bits in std::memory_order don't
work with -fshort-enums or -fstrict-enums
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Keywords: ABI
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
#include <atomic>
static_assert((std::memory_order_acquire | std::__memory_order_hle_acquire)
!= std::memory_order_acquire, "HLE acquire sets a bit");
This fails with -fshort-enums because it makes the std::memory_order enum only
occupy a single byte, so the HLE bits don't exist:
enum __memory_order_modifier
{
__memory_order_mask = 0x0ffff,
__memory_order_modifier_mask = 0xffff0000,
__memory_order_hle_acquire = 0x10000,
__memory_order_hle_release = 0x20000
};
For -fstrict-enums those bits create values which are not valid values of the
enum type.
I think we need to give std::memory_order a fixed underlying type of int, so
that its size doesn't change with -fshort-enums and all values of int are
valid.
This will be an ABI break for -fshort-enums though, but that's already happened
for PR 88996 because the new definition is a scoped enum, which always has a
fixed underlying type.
