Re: Proposed doc update for Explicit Reg Vars 3/3

[Jeff Law <law at redhat dot com>]

On 10/20/2015 11:11 AM, Segher Boessenkool wrote:
> On Tue, Oct 20, 2015 at 10:22:53AM -0600, Jeff Law wrote:
> > bz21182 has a testcase that's still helped by local register variables.
>
> I tried it out, and it now is much worse *with* the reg vars than
> without (and -O2 vs. -O3 makes no difference at all).  It doesn't look
> to have used the pre-determined allocation at all.  The difference at
> expand time is huge already; maybe some things weren't optimised at
> tree level with the register vars?  It's a bit big to really look into ;-)
We must be evaluating different things.  I review the state of that bug 
each release. While the amount of stack slot shuffling has improved over 
time it still looked better with the register variables during the gcc-5 
release cycle.

jeff