[llvm] r216066 - Optimize ZERO_EXTEND and SIGN_EXTEND in both SelectionDAG Builder and type
Jiangning Liu
liujiangning1 at gmail.com
Wed Sep 3 22:19:33 PDT 2014
Hi Rafael,
2014-08-29 19:10 GMT+08:00 Rafael EspĂndola <rafael.espindola at gmail.com>:
> On 29 August 2014 05:16, Jiangning Liu <liujiangning1 at gmail.com> wrote:
> > Hi Rafael and Bob,
> >
> > The case you gave is really huge! :-)
>
> Yes, sorry, it is the LTO of clang :-)
>
> > I tried and it turned out it is not a infinite loop, and it can finish in
> > ~70 minutes.
> >
> > I tried llc command line option -time-passes, and it shows
> >
> >
> ==-------------------------------------------------------------------------===
> > ... Pass execution timing report ...
> >
> ===-------------------------------------------------------------------------===
> > Total Execution Time: 4125.4617 seconds (4124.7082 wall clock)
> >
> > ---User Time--- --System Time-- --User+System-- ---Wall Time---
> > --- Name ---
> > 3911.0328 ( 95.1%) 8.5007 ( 65.8%) 3919.5335 ( 95.0%) 3920.7144 (
> > 95.1%) X86 DAG->DAG Instruction Selection
> > 47.5946 ( 1.2%) 0.6397 ( 5.0%) 48.2343 ( 1.2%) 48.1823 ( 1.2%)
> > Greedy Register Allocator
> > 16.7073 ( 0.4%) 0.0244 ( 0.2%) 16.7317 ( 0.4%) 16.7890 ( 0.4%)
> > Simple Register Coalescing
> > 11.6154 ( 0.3%) 0.0164 ( 0.1%) 11.6318 ( 0.3%) 11.7178 ( 0.3%)
> > Machine Instruction Scheduler
> > 10.8118 ( 0.3%) 0.0677 ( 0.5%) 10.8794 ( 0.3%) 10.3740 ( 0.3%)
> > Loop Strength Reduction
> >
> > So the problem is around "X86 DAG->DAG Instruction Selection".
> >
> > I tried to capture "hot" sports using debugger, but I failed, and it
> seems
> > the time is accumulated somewhere.
> >
> > Do you have any suggestions?
>
> You can try running llvm-extract with every function and then running
> llc on the result (which will have only one function). Hopefully you
> will find a much smaller testcase that way.
>
Thanks for your suggestion. I tried this method, and successfully
extracted 27041 functions from that huge file. However, I failed to
reproduce a small case containing a single function which can reproduce the
slowdown. The slowest function I find
is _ZN5clang15StmtVisitorBaseINS_8make_ptrENS_13ASTStmtWriterEvE5VisitEPNS_4StmtE.bc,
but it can finish in 16 seconds on my x86 box.
So it seems there are some module passes triggering the slowdown issue...
Thanks,
-Jiangning
>
> > And I'm wondering if this is a x86 specific issue or the slowdown can
> also
> > exposed for other targets like aarch64?
>
> Hard to tell without a smaller testcase.
>
> Cheers,
> Rafael
>
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