[LLVMdev] Indirect call site profiling

[betulb at codeaurora.org]

> On 10/24/2014 05:26 PM, betulb at codeaurora.org wrote:
>> Hi All,
>>
>> We've been working on enhancing LLVM's instrumentation based profiling
>> by
>> adding indirect call target profiling support. Our goal is to add
>> instrumentation around indirect call sites, so that we may track the
>> frequently taken target addresses and their call frequencies.
> Just to make sure I understand what're you describing, you're doing
> value profiling specifically for the target address of an indirect call
> through a function pointer right?

We're recording the called values at the indirect call sites. This in
essence can be considered as a type of value profiling.

>> The acquired data has uses in optimization of indirect function call
>> heavy applications. Our initial findings show that using the profile
>> data
>> in optimizations would help improve the performance of some of the spec
>> benchmarks notably. We have a proof of concept implementation,  which we
>> plan to put it up for review. However, I’d like to inquire prior if
>> there
>> are any plans or ongoing work done in the community to enable indirect
>> call target profiling support or not. Please inform if cfe-dev is a
>> better
>> candidate for posting PGO related emails.
> I'll be interested in seeing your work.  I'm interested in techniques
> for guarded devirtualization, but the profiling infrastructure should be
> fairly common.  If we could arrange the instrumentation in such a way to
> enable both use cases, we could share infrastructure.

Thanks, we've recently posted an RFC on the design. The design is quite
straightforward and simple but the gains will be seen when the data is
used in optimizations.

> Philip
>>
>> Thanks,
>> -Betul Buyukkurt
>>
>> Employee of the Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
>> Linux
>> Foundation Collaborative Project
>>
>>
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>