On Mar 13, 2006, at 6:00 PM, Peter Dimov wrote:
I'm seeing (only with inlining/optimizations on) that the reference count is not properly incremented. This is with a single-threaded test case. I haven't fully understood the code differences yet, but it appears that code is being reordered across these assembly blocks in such a way as to change the logic. I'm not familiar enough with gcc assembly semantics to know if the volatile attribute (on the assembly block itself, not any data) is required to make inline assembly behave itself.
Again, this is not a multithread issue that I can see, as the failures I'm seeing are in single threaded code.
There is a known bug in 4.0:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21528
that can have this effect, but it apparently has been fixed in 4.0.1. There might be others that the boost test doesn't uncover.
I think that the compiler is not supposed to reorder across __asm__ blocks in a way that could change the logic and if such reordering happens it should be reported as a bug against g++.
That was very kind of you to look that up for me, thanks. Since my last posting I've also become convinced that this is an optimization bug in gcc. It appears that exactly one call to atomic_increment has been optimized away. I'll investigate further whether 21528 is the cause/fix. Thanks much. -Howard