new llvm IR callbr instruction useful for proc-point splitting?
ben at well-typed.com
Thu Dec 12 19:04:54 UTC 2019
Simon Peyton Jones <simonpj at microsoft.com> writes:
> Thanks Kavon.
> What news of CpsCall in LLVM? That seems crucial.
> I didn’t know of an effort to use a different SP register. I seriously
> doubt that, with GHC’s use of zillions of small, heap-allocated stacks
> that move around during GHC, we’ll be able to leverage profiling or
> debugging tools in a serious way. But perhaps I need education.
I don't see there being a problem here:
* DWARF debugging information is expressive enough to capture GHC's
underflow frame concept, so unwinding across stack
chunks shouldn't be problematic.
* The fact that the stacks move shouldn't be a problem since
* You are using gdb, which must pause the process to look at the stack
* You are using statistical sampling profiling (e.g. perf on Linux)
which pauses the thread being sampled while capturing the stack
If you sample during a GC then you won't capture any Haskell stack
chunks so the fact that stacks might move isn't problematic; if
you sample during mutator execution then the stack is guaranteed to
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