[Bug rtl-optimization/20211] autoincrement generation is poor

["joern dot rennecke at st dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From joern dot rennecke at st dot com  2005-02-28 13:46 -------
Subject: Re:  autoincrement generation is poor

giovannibajo at libero dot it wrote:

>------- Additional Comments From giovannibajo at libero dot it  2005-02-25 18:59 -------
>What is the compile-time impact of this patch on cc-i compilation, the usual 
>C++ testcases, and SPEC? I am sure this is something worthwile to mention for 
>a review.
>  
>

Sorry, I don't have such numbers at the moment.  Note that this 
optimization is specific to
AUTO_INC_DEC targets (in principle it is possible to use it to reduce 
register pressure on
other targets too, but there is also a cost to pay in reduced 
flexibility for sched2 till you make
the scheduler aware of the possible transformations).
Note that there is a specific flag to enable or disable this 
optimization, so for each target this
can be tuned by OPTIMIZATION_OPTIONS.  I made this switch default-on at 
-O2 mainly
because it makes testing the patch much simpler.  For integration, I'm 
also fine with having it
default-off and having only the targets that want it turn it on in 
OPTIMIZATION_OPTIONS.

>And BTW, out of curiosity, does the new pass have to live in regmove.c?
>  
>
Not absolutely, but it makes sense insofar as an aspect of this 
optimization is to avoid register-register
moves  which are required when you end up with awkward register 
assignments for the addds,
and it is also nice to have sched1 run first. And there is also the 
issue fo inserting add instructions,
which needs infrastructure from regmove to avoid issues with targets 
that have a flags register that
can be clobbered by the new adds.
For the c4x, it would make sense to run this pass earlier, as detailed 
in the 1999 thread.



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20211