RE: [PATCH GCC]Relax the probability condition in CE pass when optimizing for code size

["Bin Cheng" <bin dot cheng at arm dot com>]

> -----Original Message-----
> From: Joern Rennecke [mailto:joern.rennecke@embecosm.com]
> Sent: Monday, March 25, 2013 8:53 PM
> To: Bin Cheng
> Cc: gcc-patches@gcc.gnu.org
> Subject: Re: [PATCH GCC]Relax the probability condition in CE pass when
> optimizing for code size
> 
> Quoting Bin Cheng <bin.cheng@arm.com>:
> 
> > During the work I observed passes before combine might interfere with
> > CE pass, so this patch is enabled for ce2/ce3 after combination pass.
> >
> > It is tested on x86/thumb2 for both normal and Os. Is it ok for trunk?
> 
> There are bound to be target and application specific variations on which
> scaling factors work best.
> 
> > 2013-03-25  Bin Cheng  <bin.cheng@arm.com>
> >
> > 	* ifcvt.c (ifcvt_after_combine): New static variable.
> 
> It would make more sense to pass in the scale factor as a an argument to
> if_convert.  And get the respective values from a set of gcc parameters,
so
> they can be tweaked by ports and/or by a user/ML learning framework (e.g.
> Milepost) supplying the appropriate --param option.

I agree it would be more flexible to pass the factor as parameter, but not
sure how useful to users it will be because: firstly it has already been
target specific by the BRANCH_COST heuristic; for code size, the heuristic
should be tuned to achieve an overall good results, I doubt to which extend
it depends on specific target/application.

Hi Jeff,
This is based on your heuristic tuning in ifcvt, would you help us on this
issue with some suggestions?

Thanks very much.