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

On Tue, Oct 20, 2015 at 12:01:26PM -0600, Jeff Law wrote:
> 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.

The "#if 0" variant (no reg vars) results in 3597 bytes text, "esp"
mentioned 29 times.
The "#if 1" version is 3886 bytes, "esp" mentioned 87 times.

This is a GCC 6 compiler, a week or so old.


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