On Mon, Mar 5, 2012 at 7:47 PM, Andi Kleen <a...@firstfloor.org> wrote:
> The problem I have with the flag is that the typical use model is to
> have multiple code paths, like:
>
> if (cpuid_has_rtm())
> ... do rtm ...
> else
> ... do something else ...
>
> So you have a basic block which needs RTM and another one which doesn't
> want it. If the flag would affect the code generation of the else block
> that would be bad. So essentially the flag has to be a nop anyways
> except for the intrinsic itself.
As I said, you have target pragmas exactly for this problem:
if (cpuid_has_rtm())
#pragma GCC push_options
#pragma GCC target ("rtm")
... do rtm ...
#pragma GCC pop_options
else
... do something else ...
Removing -mrtm option would remove one point of control.
Uros.
