[llvm] r216066 - Optimize ZERO_EXTEND and SIGN_EXTEND in both SelectionDAG Builder and type

[Rafael Espíndola]

Can you put that testcase somewhere?

On 4 September 2014 01:19, Jiangning Liu <liujiangning1 at gmail.com> wrote:
> Hi Rafael,
>
>
> 2014-08-29 19:10 GMT+08:00 Rafael Espíndola <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
>
>