[PATCH] D141952: [CSSPGO] Turn on postlink sample counts overwrite.

[Hongtao Yu via Phabricator via llvm-commits]

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The CS preinliner computes sample counts for outlined functions globally, resulting in a more accurate function profile than the actual thinlto postlink sample inliner does. I've seen that turning on --overwrite-existing-weights for postlink results in general 0.5% to 1% code size win (perf wise is netural) for CSSPGO accross four of our big internal services, but slight code size regression for non-CS AutoFDO.  I'm turning on the switch for preinlined profile only.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D141952

Files:
  llvm/lib/Transforms/IPO/SampleProfile.cpp


Index: llvm/lib/Transforms/IPO/SampleProfile.cpp
===================================================================
--- llvm/lib/Transforms/IPO/SampleProfile.cpp
+++ llvm/lib/Transforms/IPO/SampleProfile.cpp
@@ -2014,6 +2014,8 @@
     if (Reader->profileIsPreInlined()) {
       if (!UsePreInlinerDecision.getNumOccurrences())
         UsePreInlinerDecision = true;
+      if (!OverwriteExistingWeights.getNumOccurrences())
+        OverwriteExistingWeights = true;
     }
 
     if (!Reader->profileIsCS()) {


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