https://bugs.llvm.org/show_bug.cgi?id=38871
Bug ID: 38871
Summary: std::atomic not always atomic when compiling with GCC
Product: libc++
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: All Bugs
Assignee: unassignedclangb...@nondot.org
Reporter: richard-l...@metafoo.co.uk
CC: llvm-bugs@lists.llvm.org, mclow.li...@gmail.com
Compiling this with GCC:
#include <atomic>
struct X { char c[4]; };
std::atomic<X> x;
... results in a call to __atomic_load to load the X object. However, due to
gcc.gnu.org/PR87237, that builtin is not actually atomic in this case.
libstdc++ works around this by increasing the alignment of atomic<X> to
sizeof(X) if sizeof(X) is a power of 2 not greater than 16, so that's
presumably the set of cases where the GCC bug occurs. libc++ should probably do
the same.
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