[clang] [compiler-rt] [llvm] [TypeProf][InstrFDO]Implement more efficient comparison sequence for indirect-call-promotion with vtable profiles. (PR #81442)

[David Li via cfe-commits]

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@@ -276,35 +626,154 @@ CallBase &llvm::pgo::promoteIndirectCall(CallBase &CB, Function *DirectCallee,
 
 // Promote indirect-call to conditional direct-call for one callsite.
 bool IndirectCallPromoter::tryToPromoteWithFuncCmp(
-    CallBase &CB, const std::vector<PromotionCandidate> &Candidates,
-    uint64_t TotalCount, ArrayRef<InstrProfValueData> ICallProfDataRef,
-    uint32_t NumCandidates) {
+    CallBase &CB, Instruction *VPtr,
+    const std::vector<PromotionCandidate> &Candidates, uint64_t TotalCount,
+    ArrayRef<InstrProfValueData> ICallProfDataRef, uint32_t NumCandidates,
+    VTableGUIDCountsMap &VTableGUIDCounts) {
   uint32_t NumPromoted = 0;
 
   for (const auto &C : Candidates) {
-    uint64_t Count = C.Count;
-    pgo::promoteIndirectCall(CB, C.TargetFunction, Count, TotalCount, SamplePGO,
-                             &ORE);
-    assert(TotalCount >= Count);
-    TotalCount -= Count;
+    uint64_t FuncCount = C.Count;
+    pgo::promoteIndirectCall(CB, C.TargetFunction, FuncCount, TotalCount,
+                             SamplePGO, &ORE);
+    assert(TotalCount >= FuncCount);
+    TotalCount -= FuncCount;
     NumOfPGOICallPromotion++;
     NumPromoted++;
-  }
 
+    if (!EnableVTableProfileUse || C.VTableGUIDAndCounts.empty())
+      continue;
+
+    // After a virtual call candidate gets promoted, update the vtable's counts
+    // proportionally. Each vtable-guid in `C.VTableGUIDAndCounts` represents
+    // a vtable from which the virtual call is loaded. Compute the sum and use
+    // 128-bit APInt to improve accuracy.
+    uint64_t SumVTableCount = 0;
+    for (const auto &[GUID, VTableCount] : C.VTableGUIDAndCounts)
+      SumVTableCount += VTableCount;
+
+    for (const auto &[GUID, VTableCount] : C.VTableGUIDAndCounts) {
+      APInt APFuncCount((unsigned)128, FuncCount, false /*signed*/);
+      APFuncCount *= VTableCount;
+      VTableGUIDCounts[GUID] -= APFuncCount.udiv(SumVTableCount).getZExtValue();
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david-xl wrote:

should the denominator be the total funcCount?

https://github.com/llvm/llvm-project/pull/81442