Re: Expansion of __builtin_frame_address

[Jim Wilson <wilson at specifix dot com>]

Mark Shinwell wrote:
> Option (i), which is in all but name the "solution 5" approach [1] proposed
> last year, means that the "count == 0" case is elevated to the same level
> of importance as the "count > 0" cases, in line with the use in
> backtrace ().  The problem with this is that on platforms where the
> soft and hard FPs coincide there is going to be a slight
> performance degradation, as identified previously, whenever these
> builtins are used.

I don't have a problem with the proposed patch that implements this.  I 
didn't choose this option earlier because I didn't have a testcase that 
required it.  You have now supplied one (glibc backtrace), so I think it 
is now reasonable to go forward with this.

The workaround for the performance problem is for backend maintainers to 
add an appropriate definition for the INITIAL_FRAME_ADDRESS_RTX macro. 
Perhaps forcing the issue will provide some incentive to people to fix 
their backends.
--
Jim Wilson, GNU Tools Support, http://www.specifix.com