GCC Atomic NAND implementation

Hey Guys,

I have a newbie question about supporting the GNU atomic builtin, __sync_fetch_and_nand. It appears that LLVM 29 produces X86 assembly like the GCC versions below v4.4, i.e.


notq %rax

movq 48(%rsp), %rcx

andq %rcx, %rax

I’m looking to produce X86 assembly like GCC v4.4 and greater, i.e.


movq 48(%rsp), %rcx

andq %rcx, %rax

notq %rax

I currently have custom code to make the switch between implementations, but it’s invasive at best. Has the newer implementation already been written and I missed it? If so, could someone please point me to that code? If not, are there any plans in the near future to support the newer GCC implementation?

mcinally/MERGE_29> cat llvm.c

#include <stdio.h>

typedef int16_t T;

T a = 10;

int main() {

volatile T *p = &a;

T x = 2;

int failed = 0;

printf( “Testing %d bit objects\n”, sizeof( T ) * 8 );

p = 15; / Or any value with the 2nd bit set */


if ( ~*p != 2 ) {

failed = 1;


if ( !failed ) printf( “Test PASSED\n” );

else printf( “Test FAILED\n” );

return 0;