https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117642
Bug ID: 117642
Summary: __sync_lock_release() on 128bit integer does not
behave according to documentation
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Keywords: documentation, wrong-code
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: zsojka at seznam dot cz
Target Milestone: ---
Host: x86_64-pc-linux-gnu
Target: x86_64-pc-linux-gnu
Created attachment 59613
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59613&action=edit
reduced testcase
The documentation for the legacy __sync builtins:
https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html
says:
"GCC allows any scalar type that is 1, 2, 4 or 8 bytes in size other than the C
type _Bool or the C++ type bool."
- this is probably missing "... integer scalar type ...", as it can't be used
on float types
- it seems 16 byte types are supported as well (at least somewhere)
"If a particular operation cannot be implemented on the target processor, a
warning is generated and a call to an external function is generated."
- as far as I can say, at least when using 128bit types, no warning is
generated
"The external function carries the same name as the built-in version, with an
additional suffix ‘_n’ where n is the size of the data type."
- __sync_lock_release() on __int128 does not generate any call, potentially
generating broken code
$ cat testcase.c
__int128 t = 1;
int
main ()
{
__sync_lock_release (&t);
if (t != 0)
__builtin_abort();
}
$ x86_64-pc-linux-gnu-gcc testcase.c
$ ./a.out
Aborted
$ x86_64-pc-linux-gnu-gcc testcase.c -mcx16
$ ./a.out
