On 09/14/2016 08:01 AM, Bernd Schmidt wrote:
On 09/14/2016 03:55 PM, Segher Boessenkool wrote:
On Wed, Sep 14, 2016 at 03:08:21PM +0200, Bernd Schmidt wrote:
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.
Can you point me at a processor manual for such a chip that explains why
this would be the case?
Ponder a processor where the cost to access a register is non-uniform
and related to how long ago a particular register was used. This can
happen when the actual hardware register file is much larger than the
exposed register file (to support hardware renaming, hyperthreading,
partitioning, etc).
I imagine it could be the case if it enables
more aggressive scheduling but that's kind of one of the intended effects.
Exactly.
jeff
