-Os vs move_moveables

[Andrew Pinski]

Dale,
The original discussion of the matter and why it is turned off for 
optimize_size:
http://gcc.gnu.org/ml/gcc/1998-04/msg00995.html

The message which commented the patch:
http://gcc.gnu.org/ml/gcc/1998-05/msg00495.html

When it was done:
  Revision 1.50 / (download) - annotate - [select for diffs] , Thu May 
14 00:50:07 1998 UTC (4 years, 6 months ago) by law
Branch: MAIN
Changes since 1.49: +7 -3 lines
Diff to previous 1.49 (colored)

         * loop.c (scan_loop): Don't call move_moveables for 
optimize_size.



On Monday, Dec 9, 2002, at 11:36 US/Pacific, Dale Johannesen wrote:

> Currently the loop optimizer disables pulling things out of loops with 
> -Os:
>
>>   /* Now consider each movable insn to decide whether it is worth 
>> moving.
>>      Store 0 in regs->array[I].set_in_loop for each reg I that is 
>> moved.
>>
>>      Generally this increases code size, so do not move moveables when
>>      optimizing for code size.  */
>>
>>   if (! optimize_size)
>>     {
>>       move_movables (loop, movables, threshold, insn_count);
>
> This was true in 2.95 as well.  Can somebody explain why it's doing 
> this?
> I don't believe the comment is correct in general, at least for RISCs.
> If you're going to compute something into a register, it is no bulkier 
> to
> do it outside the loop.  I do see that pulling things out increases 
> register
> lifetimes and makes spilling more likely, but that consideration is 
> not specific
> to -Os.
>
>