llvm dev - Jun 2020 - Need help on JIT compilation speed

Hi there,

I am trying to JIT a rather big wasm bytecode program to x86 native code
and running into this JIT compilation time issue. In the first stage, I use
MCJIT to translate wasm bytecode to a single LLVM IR Module which ends up
with 927 functions. Then it took a pretty long time to apply several
optimization passes to this big IR module and finally generate x86 code.
What should I do to shorten the compilation time? Is it possible to compile
this single big IR Module with MCJIT in parallel? Is OrcV2 JIT faster than
MCJIT? Can the 'concurrent compilation' feature mentioned in Orcv2
webpage
help on this? Thanks in advance for any advice.

This is how I organized the optimization pass:

    LLVMAddBasicAliasAnalysisPass(comp_ctx->pass_mgr);
    LLVMAddPromoteMemoryToRegisterPass(comp_ctx->pass_mgr);
    LLVMAddInstructionCombiningPass(comp_ctx->pass_mgr);
    LLVMAddJumpThreadingPass(comp_ctx->pass_mgr);
    LLVMAddConstantPropagationPass(comp_ctx->pass_mgr);
    LLVMAddReassociatePass(comp_ctx->pass_mgr);
    LLVMAddGVNPass(comp_ctx->pass_mgr);
    LLVMAddCFGSimplificationPass(comp_ctx->pass_mgr);

This is how I apply passes to my single IR module (which actually includes
927 functions)

if (comp_ctx->optimize) {
      LLVMInitializeFunctionPassManager(comp_ctx->pass_mgr);
      for (i = 0; i < comp_ctx->func_ctx_count; i++)
          LLVMRunFunctionPassManager(comp_ctx->pass_mgr,
                                     comp_ctx->func_ctxes[i]->func);
  }

BR,
Terry
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Hi Terry,
CC'ed lang hames he is the best person to answer.

In general, ORCv2 is the new and stable JIT environment. In order to have a
fast compilation time you can use the -lazy compilation option in ORCv2,
this will result in fast compile time and interleave compile time with
execution time. You can also use the concurrent compilation option in ORCv2
to speedup. Additionally, we did a new feature called "speculative
compilation" in ORcv2 which yields good results for a set of benchmarks. If
you are interested please try this out. We would like to have some
benchmarks on your case :)
To try things out you can check out the examples directory in LLVM for
ExecutionEngine.
I hope this helps

On Tue, 16 Jun 2020 at 21:10, Terry Guo via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi there,
>
> I am trying to JIT a rather big wasm bytecode program to x86 native code
> and running into this JIT compilation time issue. In the first stage, I use
> MCJIT to translate wasm bytecode to a single LLVM IR Module which ends up
> with 927 functions. Then it took a pretty long time to apply several
> optimization passes to this big IR module and finally generate x86 code.
> What should I do to shorten the compilation time? Is it possible to compile
> this single big IR Module with MCJIT in parallel? Is OrcV2 JIT faster than
> MCJIT? Can the 'concurrent compilation' feature mentioned in Orcv2
webpage
> help on this? Thanks in advance for any advice.
>
> This is how I organized the optimization pass:
>
>     LLVMAddBasicAliasAnalysisPass(comp_ctx->pass_mgr);
>     LLVMAddPromoteMemoryToRegisterPass(comp_ctx->pass_mgr);
>     LLVMAddInstructionCombiningPass(comp_ctx->pass_mgr);
>     LLVMAddJumpThreadingPass(comp_ctx->pass_mgr);
>     LLVMAddConstantPropagationPass(comp_ctx->pass_mgr);
>     LLVMAddReassociatePass(comp_ctx->pass_mgr);
>     LLVMAddGVNPass(comp_ctx->pass_mgr);
>     LLVMAddCFGSimplificationPass(comp_ctx->pass_mgr);
>
> This is how I apply passes to my single IR module (which actually includes
> 927 functions)
>
> if (comp_ctx->optimize) {
>       LLVMInitializeFunctionPassManager(comp_ctx->pass_mgr);
>       for (i = 0; i < comp_ctx->func_ctx_count; i++)
>           LLVMRunFunctionPassManager(comp_ctx->pass_mgr,
>                                      comp_ctx->func_ctxes[i]->func);
>   }
>
> BR,
> Terry
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hi Praveen,

Thanks for your help. I will follow your suggestions and get back if I can
make some progress.

BR,
Terry


On Wed, Jun 17, 2020 at 12:12 AM Praveen Velliengiri <
praveenvelliengiri at gmail.com> wrote:
> Hi Terry,
> CC'ed lang hames he is the best person to answer.
>
> In general, ORCv2 is the new and stable JIT environment. In order to have
> a fast compilation time you can use the -lazy compilation option in ORCv2,
> this will result in fast compile time and interleave compile time with
> execution time. You can also use the concurrent compilation option in ORCv2
> to speedup. Additionally, we did a new feature called "speculative
> compilation" in ORcv2 which yields good results for a set of
benchmarks. If
> you are interested please try this out. We would like to have some
> benchmarks on your case :)
> To try things out you can check out the examples directory in LLVM for
> ExecutionEngine.
> I hope this helps
>
> On Tue, 16 Jun 2020 at 21:10, Terry Guo via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi there,
>>
>> I am trying to JIT a rather big wasm bytecode program to x86 native
code
>> and running into this JIT compilation time issue. In the first stage, I
use
>> MCJIT to translate wasm bytecode to a single LLVM IR Module which ends
up
>> with 927 functions. Then it took a pretty long time to apply several
>> optimization passes to this big IR module and finally generate x86
code.
>> What should I do to shorten the compilation time? Is it possible to
compile
>> this single big IR Module with MCJIT in parallel? Is OrcV2 JIT faster
than
>> MCJIT? Can the 'concurrent compilation' feature mentioned in
Orcv2 webpage
>> help on this? Thanks in advance for any advice.
>>
>> This is how I organized the optimization pass:
>>
>>     LLVMAddBasicAliasAnalysisPass(comp_ctx->pass_mgr);
>>     LLVMAddPromoteMemoryToRegisterPass(comp_ctx->pass_mgr);
>>     LLVMAddInstructionCombiningPass(comp_ctx->pass_mgr);
>>     LLVMAddJumpThreadingPass(comp_ctx->pass_mgr);
>>     LLVMAddConstantPropagationPass(comp_ctx->pass_mgr);
>>     LLVMAddReassociatePass(comp_ctx->pass_mgr);
>>     LLVMAddGVNPass(comp_ctx->pass_mgr);
>>     LLVMAddCFGSimplificationPass(comp_ctx->pass_mgr);
>>
>> This is how I apply passes to my single IR module (which actually
>> includes 927 functions)
>>
>> if (comp_ctx->optimize) {
>>       LLVMInitializeFunctionPassManager(comp_ctx->pass_mgr);
>>       for (i = 0; i < comp_ctx->func_ctx_count; i++)
>>           LLVMRunFunctionPassManager(comp_ctx->pass_mgr,
>>                                     
comp_ctx->func_ctxes[i]->func);
>>   }
>>
>> BR,
>> Terry
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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