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

[David Li via llvm-commits]

================
@@ -90,9 +90,33 @@ public:
   }
 };
 
+///------------------------ VirtualTableValueProfilingPlugin ------------------------
+class VTableProfilingPlugin {
+  Function &F;
+
+public:
+  static constexpr InstrProfValueKind Kind = IPVK_VTableTarget;
+
+  VTableProfilingPlugin(Function &Fn, TargetLibraryInfo &TLI) : F(Fn) {}
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david-xl wrote:

The candidate selection can be more restrictive to make the vtable value profiling more runtime efficient (value profiling is expensive).  

for the following example where ptr points to a polymorphic type,

for ( i = 0 ; i < 1000;i++) {
    ptr->func1();
    ptr->func2();
    ptr->func3();
}

instead of doing value profiling at each each callsite (expensive), do the following:

__instrument_value_profile(site_id, ptr->vfptr);
for (....) {
   ptr->func1();
   ...
}

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