As I understand __sync_synchronize, the intent is to emit a memory barrier
instruction, at least on multiprocessor systems. Currently on x86
__sync_synchronize inhibits explicit code motion across the builtin function
call but not processor reordering of memory operations across the builtin
function call.
I think mfence is the right instruction on x86-64, and this or a similar
pattern should be added to sync.md:
(define_insn "memory_barrier"
[(unspec_volatile [(const_int 0)] UNSPEC_MFENCE)]
"TARGET_SSE2"
"mfence")
--
Summary: x86-64 does not get __sync_synchronize right
Product: gcc
Version: 4.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jfc at mit dot edu
GCC build triplet: x86_64-linux-gnu
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36793
