Richard Biener wrote:
> On Wed, Aug 20, 2014 at 10:29 PM, Sebastian Pop <seb...@gmail.com> wrote:
> > James Greenhalgh wrote:
> >> On Tue, Aug 19, 2014 at 09:39:56PM +0100, Steve Ellcey wrote:
> >> > Here is an official submission for the switch optimization described in
> >> > PR 54742. I have addressed the formatting/comment issues that were
> >> > raised
> >> > and also added a test case based on comment #27 from PR 54742 and I
> >> > fixed a
> >> > bug I found while doing benchmarking with SPEC2006 (the perl benchmark
> >> > was
> >> > generating an ICE in a routine with multiple switch statements).
> >> >
> >> > I ran the benchmarking to see if I could find any more tests that are
> >> > helped like coremark is and while I found a number of benchmarks in
> >> > SPEC 2006 and EEMBC where the optimization is triggered, this
> >> > optimization
> >> > generally didn't affect the performance of those benchmarks. The biggest
> >> > impact I could find was on the perl benchmark in SPEC where I saw around
> >> > a 0.4% improvement on a MIPS 74k. Not huge, but not nothing.
> >>
> >> For what it is worth, I see a nice (~4%) improvement in Crafty from
> >> SPEC 2000. I haven't investigated too deeply, but at a first glance the
> >> number of branch mispredictions has dropped just over 1%, as you
> >> might hope from this optimisation.
> >>
> >> I can also attest to there being a number of places the optimisation is
> >> triggered (with high enough parameters; I was running with
> >> --param max-switch-paths=1000 --param max-switch-insns=10000), but like
> >> you I don't see much measurable change in execution time.
> >
> > Without change to the default params, I see the switch shortcut having a
> > performance impact on both png and jpeg, compress and decompress mode.
> >
> > I think that's enough to remove the "benchmarketing" label from the switch
> > shortcut transform.
>
> Did you look at the actual code transformation the pass does to these?
> (what is 'png' and 'jpeg'?) What's the code size impact?
google("jddctmgr.c") the start_pass function contains a for loop with a switch
stmt that is optimized by Steve's pass.
The png one occurs in google("pngread.c png_image_read_colormap")
There is not much code duplicated in both cases.
Sebastian
