[PATCH] D125743: [outliner] Use profile data to avoid outlining hot blocks

[Wenlei He via Phabricator via llvm-commits]

wenlei added inline comments.


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Comment at: llvm/lib/CodeGen/MachineOutliner.cpp:119
+static cl::opt<bool>
+    UseProfileData("machine-outliner-use-profile-data", cl::init(false),
+                   cl::Hidden,
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I don't think we do this for other passes. Once the plumbing for BFI/MBFI is done for passes to leverage profile info, we just always do that. Using profile should indeed always be better if heuristic is reasonable. Why you need a flag for this case? 

If you need some confidence in profile quality, you can check on profile (`PSI->hasInstrumentationProfile()`) etc.


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Comment at: llvm/lib/CodeGen/MachineOutliner.cpp:379
+    if (UseProfileData) {
+      AU.addRequired<BlockFrequencyInfoWrapperPass>();
+      AU.addRequired<ProfileSummaryInfoWrapperPass>();
----------------
Why do we require BFI instead of MBFI given this is dealing with MIR.


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Comment at: llvm/lib/CodeGen/MachineOutliner.cpp:943
+        continue;
+      // TODO: Should we use isHotBlockNthPercentile() instead?
+
----------------
Usually we call higher level API like isHotBlock instead of isHotBlockNthPercentile. You can tweak the global percentile by `-profile-summary-cutoff-hot`. 


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D125743/new/

https://reviews.llvm.org/D125743