[clang] [IRPGO][ValueProfile] Instrument virtual table address that could be used to do virtual table address comparision for indirect-call-promotion. (PR #66825)

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modiking wrote:

> Yes there are tradeoffs to doing this purely with whole program class hierarchy analysis vs with profiled type info, and in fact they can be complementary. For example, the profile info can indicate what order to do the vtable comparisons (i.e. descending order of hotness, as we do for vfunc comparisons in current ICP), while WP CHA can be used to determine when no fallback is required. Also, another advantage of doing this with profiling is also that it does not require WP visibility, which may be difficult to guarantee.

Gotcha, that makes sense. Are there plans on your side to extend this level of value profiling/WP CHA to AutoFDO? I'm looking into trying out the WP CHA approach on my side since it looks like there are cases it can catch in our internal workloads.

https://github.com/llvm/llvm-project/pull/66825