https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85595
Bug ID: 85595
Summary: __atomic_is_lock_free(sizeof(unsigned long long), &v)
returns true on i686
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: aivchenk at gmail dot com
Target Milestone: ---
in gcc __atomic_is_lock_free(sizeof(unsigned long long), &v) returns true (in
clang it is left as a call)
int main()
{
unsigned long long v;
if (__atomic_is_lock_free(sizeof(unsigned long long), &v))
return 0;
else
return 1;
}
> g++ -O2 -m32 -std=gnu++11 -fno-exceptions -fno-rtti
main:
.LFB0:
xorl %eax, %eax
ret
> clang++ -O2 -m32 -std=gnu++11 -fno-exceptions -fno-rtti
main: # @main
.Lfunc_begin0:
# %bb.0:
subl $12, %esp
.Ltmp0:
subl $8, %esp
leal 8(%esp), %eax
pushl %eax
pushl $8
calll __atomic_is_lock_free
addl $16, %esp
xorl %ecx, %ecx
testl %eax, %eax
sete %cl
.Ltmp1:
movl %ecx, %eax
addl $12, %esp
retl
__atomic_is_lock_free always should return false for misaligned pointers (long
long is only 4-byte aligned on i686)
More details can be found at the bug filed against llvm
https://bugs.llvm.org/show_bug.cgi?id=36860
