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

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

On Sat, Nov 26, 2016 at 09:15:48AM -0700, Jeff Law wrote:
> On 11/26/2016 04:11 AM, Eric Botcazou wrote:
> >> From my investigations on the m68k, the effects on the IL are minimal
> >>with a slight bias towards better code (by suppressing if-conversions of
> >>some now more costly blocks).  *But* the size of the resulting code was
> >>all over the place -- sometimes it was better, others worse.  From
> >>looking at the assembly we seemingly are copying blocks that aren't
> >>strictly necessary.
> >
> >I'm seeing essentially the same thing on SPARC, probably because of the 
> >ifcvt
> >change; the rtlanal change seems to be neutral for the architecture.
> Just to be clear, I was only testing the rtlanal change, not the ifcvt 
> change.
> 
> I repeated my test on the GCC runtime libraries for m68k-elf.  Bernd's 
> rtlanal change +.03%, the goof in STC, +9.4%.  So the STC goof still 
> dwarfs the impact to Bernd's change, but not as badly as I saw in the 
> newlib codebase.

orig, i386+rtlanal, i386+rtlanal+ifcvt:

worse:
       alpha   5439003   5455979   5455979
         c6x   2107939   2108931   2108931
        cris   2189380   2193836   2193836
        m32r   3427409   3427541   3427453
        m68k   3228408   3230978   3230978
        mips   4286748   4286964   4286692
      mips64   5564819   5565643   5565291
      parisc   8278881   8289977   8289573
    parisc64   7234619   7249187   7249139
     powerpc   8438949   8440005   8440005
   powerpc64  14499969  14508689  14508689
        s390  12778748  12779228  12779220
     shnommu   1369868   1371020   1371020
     sparc64   5921556   5922172   5922172
      tilegx  12297581  12307461  12307461
     tilepro  11215603  11227339  11227339
      xtensa   1776196   1779152   1779152

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

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


tl;dr: The ifcvt change doesn't do much, but the cost change does.


Segher