https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96056
Bug ID: 96056
Summary: arm v6/v7: Missing acquire barrier for
__atomic_compare_exchange(__ATOMIC_RELEASE,
__ATOMIC_ACQUIRE)
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: izbyshev at ispras dot ru
CC: amonakov at gcc dot gnu.org
Target Milestone: ---
$ cat test.c
void foo(int x, int y, int z) {
__atomic_compare_exchange(&x, &y, &z, 0, __ATOMIC_RELEASE,
__ATOMIC_ACQUIRE);
}
$ arm-linux-gnueabi-gcc-10 -O2 -march=armv7 -S -o - test.c
[...]
sub sp, sp, #8
str r0, [sp, #4]
add r0, sp, #4
dmb ish
.L2:
ldrex r3, [r0]
cmp r3, r1
bne .L3
strex ip, r2, [r0]
cmp ip, #0
bne .L2
.L3:
@ <=== missing dmb here
add sp, sp, #8
[...]
Changing __ATOMIC_RELEASE to __ATOMIC_ACQ_REL restores the missing barrier.
The same problem applies to armv6 as well.
I've checked that all GCC versions on gcc.godbolt.org since 5.4.0 behave in the
same way. All Clang versions on godbolt don't have this problem.
