[4.5] Find more autoinc addressing for induction variables

Bernd Schmidt bernds_cb1@t-online.de
Wed May 13 22:16:00 GMT 2009


Steven Bosscher wrote:
> On Wed, May 13, 2009 at 5:53 PM, Bernd Schmidt <bernds_cb1@t-online.de> wrote:
>> I wrote:
>>> The current auto-inc-dec optimization only looks at single basic blocks,
>>> and fails to create autoincrement addressing for induction variables in
>>> nontrivial loops.
>>>
>>> This patch tries to address this.  When we have a suitable memory
>>> reference, we look for two definitions using DU/UD chains: an
>>> initialization, and an increment, which must satisfy a number of
>>> conditions (see comments in the patch).
>> http://gcc.gnu.org/ml/gcc-patches/2009-02/msg00729.html
>>
>> Ping.
> 
> Perhaps I missed it, but did you address Paolo's comment
> (http://gcc.gnu.org/ml/gcc-patches/2009-02/msg00736.html), for example
> by looking at what this does to compilation times?

Paolo suggested enabling it at -O2 only.  I'd be happy to make that 
change if someone wants to approve it under that condition.  However, I 
was hoping for a more substantive review that goes towards approving or 
rejecting the patch.

I'm puzzled that we were promised all this shiny new df infrastructure 
and now it's supposedly too expensive to use?


Bernd
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