On Tue, Feb 6, 2018 at 12:37 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>
> Are there any compilers that would miscompile:
>
> mask = 0 - (index < size);
>
> That might be a way to improve the assembly.
Sadly, that is *very* easy to miscompile. In fact, I'd be very
surprised indeed if any compiler worth its name wouldn't combine the
comparison with the conditional branch it accompanies, and just turn
that into a constant. IOW, you'd get
mask = 0 - (index < size);
if (index <= size) {
... use mask ..
and the compiler would just turn that into
if (index <= size) {
mask = -1;
and be done with it.
Linus
