[LLVMdev] RDPMC inst use in llvm

[John Criswell]

On 6/20/14, 4:31 PM, sathvik wrote:
> Hi John,
>
> I don't think its possible to add/insert an inline assembly into the 
> LLVM IR unless the IR interface provides some kind of stream writer 
> into which inline instructions can be written into.

The LLVM IR supports inline assembly instructions.  See the Language 
Reference Manual and the doxygen information on the llvm::InlineAsm class.

>
> I was thinking having an LLVM intrinsic function could be a first step 
> towards introducing PMU tool support in LLVM with which you can 
> generate code with built-in instrumentation. What do you think ?

If you wanted to build a processor-independent tool to collect the 
information that RDPMC provides, then I think an intrinsic would be the 
way to go.  However, that might be a greater goal than what you 
currently need.  It certainly seems like a difficult issue to make them 
portable given how different PMCs are across different Intel processors.

Regards,

John Criswell
>
> Sathvik
>
>
>
>
>
>
> On Fri, Jun 20, 2014 at 8:21 AM, John Criswell <criswell at illinois.edu 
> <mailto:criswell at illinois.edu>> wrote:
>
>     On 6/19/14, 7:12 PM, sathvik wrote:
>>     I want to measure the performance of a JITed code snippet on MCJIT.
>>     so I was planning to inject the RDPMC inst for the code generated
>>     through a llvm IR builder.
>
>     I assume the easier way to do this is to add an inline assembly
>     call that uses the RDPMC instruction.  I don't think there's an
>     LLVM IR intrinsic function that does it.
>
>     Regards,
>
>     John Criswell
>
>>
>>     Is there a patch available ? If there's a better way to do it
>>     please chime in.
>>
>>     Thanks
>>     sathvik
>>
>>
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>

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