rsmith added a comment. Clang's `<stdatomic.h>` uses the builtin as follows:
#define atomic_is_lock_free(obj) __c11_atomic_is_lock_free(sizeof(*(obj))) ... which, combined with the builtin returning `int`, results in a call having the wrong type. So there's definitely a bug *somewhere*. I think what happened here is: the return type of the GCC `__atomic_is_lock_free` / `__atomic_always_lock_free` builtins was `int` in GCC 4.6 and earlier, and changed to `_Bool` in GCC 4.7 and later. Clang's implementation followed GCC's behavior at the time, so returned `int`, and no-one noticed that GCC changed its behavior in version 4.7. So we still provide the old GCC behavior. Then, when `__c11_atomic_is_lock_free` was added, it got an `int` return type as (I think) a copy-paste error. The `__c11` builtins are intended to exactly match the semantics of the C11 atomic functions, so this was always wrong. I think we should make this change, to all three affected builtin functions. ================ Comment at: clang/include/clang/Basic/Builtins.def:756 BUILTIN(__atomic_signal_fence, "vi", "n") BUILTIN(__atomic_always_lock_free, "izvCD*", "n") +BUILTIN(__atomic_is_lock_free, "bzvCD*", "n") ---------------- This one is also wrong, and should return *bool*. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D79504/new/ https://reviews.llvm.org/D79504 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
