[PATCH] D18489: [PGO] Comment how function pointers for indirect calls are mapped to function names

[Adam Nemet via cfe-commits]

anemet created this revision.
anemet added reviewers: bogner, davidxl.
anemet added a subscriber: cfe-commits.

Hopefully this will make it easier for the next person to figure all
this out...

http://reviews.llvm.org/D18489

Files:
  lib/CodeGen/CodeGenPGO.cpp

Index: lib/CodeGen/CodeGenPGO.cpp
===================================================================
--- lib/CodeGen/CodeGenPGO.cpp
+++ lib/CodeGen/CodeGenPGO.cpp
@@ -755,6 +755,14 @@
   if (!ValuePtr || !ValueSite || !Builder.GetInsertBlock())
     return;
 
+  // During instrumentation, function pointers are collected for the different
+  // indirect call targets.  Then as part of the conversion from raw to merged
+  // profile data, these get replaced with md5 function name hashes.  (This
+  // actually happens during deserialization of the raw profdata.)
+  //
+  // For this remapping the ProfData is used.  ProfData contains both the
+  // function name hash and the function address.
+
   bool InstrumentValueSites = CGM.getCodeGenOpts().hasProfileClangInstr();
   if (InstrumentValueSites && RegionCounterMap) {
     llvm::LLVMContext &Ctx = CGM.getLLVMContext();


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