Re: [0/3] Fix PR78120, in ifcvt/rtlanal/i386.

[Segher Boessenkool <segher@kernel.crashing.org>]

On Thu, Nov 24, 2016 at 10:14:24AM -0600, Segher Boessenkool wrote:
> On Thu, Nov 24, 2016 at 08:48:04AM -0700, Jeff Law wrote:
> > On 11/24/2016 07:53 AM, Segher Boessenkool wrote:
> > >
> > >That we compare different kinds of costs (which really has no meaning at
> > >all, it's a heuristic at best) in various places is a known problem, not
> > >a regression.
> > But the problems with the costing system exhibit themselves as a code 
> > quality regression.  In the end that's what the end-users see -- a 
> > regression in the quality of the code GCC generates.
> 
> Yes, exactly -- and I fear this all-encompassing change will cause just
> such a regression for many users.  Tests are running, will know more
> later today (or tomorrow).
> 
> The PR is about a very specific problem; the patch is not.  The patch
> is not a bug fix.  If we allow anything that "makes things better" in
> stage 3, what make it different from stage 1 then?

Here are results of testing with trunk right before the three patches,
compared with with the three patches.  This lists the sizes of the vmlinux
of a Linux kernel build for that arch.


better:
    blackfin   1973931   1973867
         frv   3638192   3637792
       h8300   1060172   1059976
        i386   9742984   9742463
        ia64  15402035  15396171
        mips   4286748   4286692
     mn10300   2360025   2358201
       nios2   3185625   3176693
      x86_64  10360418  10359588

worse:
       alpha   5439003   5455979
         c6x   2107939   2108931
        cris   2189380   2193836
        m32r   3427409   3427453
        m68k   3228408   3230978
      mips64   5564819   5565291
      parisc   8278881   8289573
    parisc64   7234619   7249139
     powerpc   8438949   8440005
   powerpc64  14499969  14508689
        s390  12778748  12779220
     shnommu   1369868   1371020
     sparc64   5921556   5922172
      tilegx  12297581  12307461
     tilepro  11215603  11227339
      xtensa   1776196   1779152

does not build:
         arc         0         0
         arm         0         0
       arm64         0         0
  microblaze         0         0
          sh         0         0
       sparc         0         0


Segher