[LLVMdev] LLVM 3.3 JIT code speed

[Eli Friedman]

On Thu, Jul 18, 2013 at 9:07 AM, Stéphane Letz <letz at grame.fr> wrote:
> Hi,
>
> Our DSL LLVM IR emitted code (optimized with -O3 kind of IR ==> IR passes) runs slower when executed with the LLVM 3.3 JIT, compared to what we had with LLVM 3.1. What could be the reason?
>
> I tried to play with TargetOptions without any success…
>
> Here is the kind of code we use to allocate the JIT:
>
>     EngineBuilder builder(fResult->fModule);
>     builder.setOptLevel(CodeGenOpt::Aggressive);
>     builder.setEngineKind(EngineKind::JIT);
>     builder.setUseMCJIT(true);
>     builder.setCodeModel(CodeModel::JITDefault);
>     builder.setMCPU(llvm::sys::getHostCPUName());
>
>     TargetOptions targetOptions;
>     targetOptions.NoFramePointerElim = true;
>     targetOptions.LessPreciseFPMADOption = true;
>     targetOptions.UnsafeFPMath = true;
>     targetOptions.NoInfsFPMath = true;
>     targetOptions.NoNaNsFPMath = true;
>     targetOptions.GuaranteedTailCallOpt = true;
>
>    builder.setTargetOptions(targetOptions);
>
>     TargetMachine* tm = builder.selectTarget();
>
>     fJIT = builder.create(tm);
>     if (!fJIT) {
>         return false;
>     }
>     ….
>
> Any idea?

It's hard to say much without seeing the specific IR and the code
generated from that IR.

-Eli