[LLVMdev] Counting instructions in MCJIT

[Jim Grosbach]

Hi Verena,

There's currently no explicit support for that, no. The MCJIT uses the same pass handling as the static compiler. In particular, it uses TargetMachine::addPassesToEmitMC().

Where you likely really want to hook into the process is the MCStreamer's EmitInstruction() method, as that really will be a 1:1 mapping to machine instructions, including any that come from pseudo-instructions or even inline assembly.

Regards,
  Jim

On Jun 27, 2012, at 2:22 AM, Verena Beckham <verena at codeplay.com> wrote:

> Hi there,
> 
> I wondered whether anyone could give me any advice about counting 
> assembly instructions when using MCJIT?
> For performance regression testing I would like to be able to count the 
> number of instructions generated during the jit compilation of a given 
> module.
> 
> The Statistic class, as far as I understand, cannot collect this data 
> per-module (per-ExecutionEngine/per-MCJIT), and there is no way of 
> extracting a single statistic without doing string manipulation. I'm 
> also doing several code gens in parallel, so even if the class is 
> thread-safe, I cannot find the values for the single modules.
> 
> In JIT you can add a JITListener, which can count the 
> MachineInstructions, with the assumption that there is a (more or less) 
> 1-2-1 mapping between machine and assembly instructions. Is there 
> something equivalent for MCJIT?
> 
> I can write a MachineFunctionPass to do the same, but I can find no way 
> of inserting that into the PassManager that MCJIT uses. This means I'm 
> replicating the passes and doing code gen twice, basically.
> 
> Any advice would be much appreciated!
> Thank you very much,
> 
> -- 
> Verena Beckham
> 
> Vice President Engineering
> 
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