[compiler-rt] [llvm] [InstrPGO][TypeProf]Annotate vtable types when they are present in the profile (PR #99402)

[Teresa Johnson via llvm-commits]

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@@ -1755,8 +1757,22 @@ void PGOUseFunc::annotateValueSites() {
 void PGOUseFunc::annotateValueSites(uint32_t Kind) {
   assert(Kind <= IPVK_Last);
   unsigned ValueSiteIndex = 0;
-  auto &ValueSites = FuncInfo.ValueSites[Kind];
+
   unsigned NumValueSites = ProfileRecord.getNumValueSites(Kind);
+
+  // Since there isn't a reliable or fast way for profile reader to tell if a
+  // profile is generated with `-enable-vtable-value-profiling` on, we run the
+  // value profile collector over the function IR to find the instrumented sites
+  // iff function profile records shows the number of instrumented vtable sites
+  // is not zero. Function cfg already takes the number of instrumented
+  // indirect call sites into account so it doesn't hash the number of
+  // instrumented vtables; as a side effect it makes it easier to enable
+  // profiling and profile use in two steps if needed.
+  if (NumValueSites > 0 && Kind == IPVK_VTableTarget &&
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teresajohnson wrote:

Can we add a TODO to remove this if/when `-enable-vtable-value-profiling` is on by default?

https://github.com/llvm/llvm-project/pull/99402