[PATCH] D97673: [RFC] [[Coroutine] [Debug] Salvage dbg.value at O2

[Chuanqi Xu via Phabricator via llvm-commits]

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The previous implementation of coro-split didn't collect values used by dbg instructions into the spills which made a log debug info unavailable at O2 <https://reviews.llvm.org/owners/package/2/>.
This patch tries to collect these uses which are used by dbg.values. In this way, the debugbility of coroutine could be as powerful as normal functions at O2 <https://reviews.llvm.org/owners/package/2/>.
However, the coroutine frame may get larger after this patch. Consider following example:

  %0 = bitcast %a to ...
  call dbg.value(metadata %0, ...) // %0 is only used in this instruction 

%0 would be put in the coroutine frame after this patch, which is obviously redundant. Considering O2 <https://reviews.llvm.org/owners/package/2/> would lose many debug information naturally, it makes no sense to weaken the speed/size for debug info. So maybe we need to add an option for this patch.

Further more, the example above shows an optimization chance when constructing coroutine frame: if we can calculate a value in the frame only by other values in the frame, then the first value isn't necessary. This idea resembles the process of rematerialization  in register allocation. Although we have a lot of resources to build the frame, I think such optimization could be valuable.

Test-plan: check-llvm


https://reviews.llvm.org/D97673

Files:
  llvm/lib/Transforms/Coroutines/CoroFrame.cpp
  llvm/lib/Transforms/Coroutines/CoroInternal.h
  llvm/test/Transforms/Coroutines/coro-debug-dbg.values-O2.ll

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