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

[Jiangning Liu]

Hi Rafael and Bob,

The case you gave is really huge! :-)

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?

And I'm wondering if this is a x86 specific issue or the slowdown can also
exposed for other targets like aarch64?

Thanks,
-Jiangning



2014-08-21 11:07 GMT+08:00 Rafael Espíndola <rafael.espindola at gmail.com>:

> On 20 August 2014 22:10, Jiangning Liu <liujiangning1 at gmail.com> wrote:
> > Hi Rafael and Bob,
> >
> > Sorry about that! I've just reverted 216066.
>
> Thanks. I just tested with  r216149 and the slowdown is gone.
>
> Cheers,
> Rafael
>
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