[LLVMdev] Slow jitter.

[Óscar Fuentes]

Hello Török.

Török Edwin <edwintorok at gmail.com> writes:

> On 2009-08-26 16:57, Óscar Fuentes wrote:
>> llc needs 45 seconds. This is far worse than the 33 seconds used by the
>> JIT. Maybe llc is using optimizations. My JIT have no optimizations
>> enabled.
>>
>> Yup, llc -O0 takes 37.5 seconds.
>>
>> llc -pre-RA-sched=fast -regalloc=local takes 26 seconds. Much better but
>> still slow IMO. The question is if this avoids the non-linear algorithms
>> and if the generated code is faster enough to justify LLVM. I'll do some
>> experimentation.
>>
>> The generated assembly file is 290K lines for unadorned llc and 616K
>> lines for -pre-RA-sched=fast -regalloc=local. This does not inspire much
>> hope :-)
>
> Is this a Release or a Release-Asserts build?
> You could try how much time it takes on a Release-Asserts build.

Assertions are disabled.

> Also if you use -time-passes with llc it should show which pass in llc
> takes so much time.

These are the three main culprits for llc -O0

   ---User Time---   --System Time--   --User+System--   ---Wall Time---  --- Name ---
  10.9531 ( 30.0%)   0.4687 ( 58.8%)  11.4218 ( 30.6%)  11.5468 ( 30.6%)  X86 DAG->DAG Instruction Selection
  10.2500 ( 28.0%)   0.0156 (  1.9%)  10.2656 ( 27.5%)  10.2500 ( 27.2%)  Live Variable Analysis
   4.8593 ( 13.3%)   0.0000 (  0.0%)   4.8593 ( 13.0%)   4.8593 ( 12.9%)  Linear Scan Register Allocator

And there for -pre-RA-sched=fast -regalloc=simple -O0 code.bc

  10.7187 ( 45.4%)   0.4375 ( 60.8%)  11.1562 ( 45.8%)  11.1718 ( 45.4%)  X86 DAG->DAG Instruction Selection
   7.4687 ( 31.6%)   0.0156 (  2.1%)   7.4843 ( 30.7%)   7.5312 ( 30.6%)  Simple Register Allocator
   1.9531 (  8.2%)   0.1406 ( 19.5%)   2.0937 (  8.6%)   2.1093 (  8.5%)  X86 Intel-Style Assembly Printer

I suppose we can't get rid of instruction selection :-)

-- 
Óscar