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Re: [PATCH 5/9] regrename: Don't run if function was separately shrink-wrapped
On Wed, Sep 14, 2016 at 03:08:21PM +0200, Bernd Schmidt wrote:
> On 09/14/2016 03:04 PM, Segher Boessenkool wrote:
> >Then rs6000 (and many other ports probably) will just turn it off again.
> >It is actively harmful.
>
> The data that was posted showed a code size decrease on a number of
> targets. I'm really not sure where this irrational hate for regrename
> comes from.
It increases the number of active, "young" registers per thread.
There is no irrational hate. Regrename is simply a de-optimisation on
some (heavily) out-of-order targets. Not by much, but not a win either.
We would rather do without it, on current CPUs at least (and I doubt this
will change soon, but we'll see).
(It also makes the generated code much harder to read, but you know that).
Segher