[clang] [IRPGO][ValueProfile] Instrument virtual table address that could be used to do virtual table address comparision for indirect-call-promotion. (PR #66825)

[Mingming Liu via cfe-commits]

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@@ -19,20 +19,38 @@ namespace llvm {
 // Visitor class that finds all indirect call.
 struct PGOIndirectCallVisitor : public InstVisitor<PGOIndirectCallVisitor> {
   std::vector<CallBase *> IndirectCalls;
+  std::vector<Instruction *> VTableAddrs;
   PGOIndirectCallVisitor() = default;
 
   void visitCallBase(CallBase &Call) {
     if (Call.isIndirectCall())
-      IndirectCalls.push_back(&Call);
+      if (Call.isIndirectCall()) {
+        IndirectCalls.push_back(&Call);
+
+        LoadInst *LI = dyn_cast<LoadInst>(Call.getCalledOperand());
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minglotus-6 wrote:

It makes sense to improve usability. Updated description of option `enable-vtable-value-profiling` in this commit for this purpose.

I wonder if clang is a better place to validate user options, considering
1) fwhole-program-vtables are clang options; and IRPGO looks at type metadata / intrinsics generated by language frontend.
2) when vtable instrumentation (along with the optimization that uses it) is rolled out to be default, a simple c++ binary which doesn't use class inheritance could pick up the compiler flag change; and a warning is not expected for this simple binary.



https://github.com/llvm/llvm-project/pull/66825