diff --git a/llvm/include/llvm/LTO/LTO.h b/llvm/include/llvm/LTO/LTO.h
index d8e632b5a49d5..d5e7d2ede7e9b 100644
--- a/llvm/include/llvm/LTO/LTO.h
+++ b/llvm/include/llvm/LTO/LTO.h
@@ -464,6 +464,19 @@ class LTO {
     ModuleMapType ModuleMap;
     // The bitcode modules to compile, if specified by the LTO Config.
     std::optional<ModuleMapType> ModulesToCompile;
+
+    void setPrevailingModuleForGUID(GlobalValue::GUID GUID, StringRef Module) {
+      PrevailingModuleForGUID[GUID] = Module;
+    }
+    bool isPrevailingModuleForGUID(GlobalValue::GUID GUID,
+                                   StringRef Module) const {
+      auto It = PrevailingModuleForGUID.find(GUID);
+      return It != PrevailingModuleForGUID.end() && It->second == Module;
+    }
+
+  private:
+    // Make this private so all accesses must go through above accessor methods
+    // to avoid inadvertently creating new entries on lookups.
     DenseMap<GlobalValue::GUID, StringRef> PrevailingModuleForGUID;
   } ThinLTO;
 
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 73e79c08a56ca..3c6951d8ec5fe 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1035,63 +1035,59 @@ Error LTO::linkRegularLTO(RegularLTOState::AddedModule Mod,
 Error LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
                       const SymbolResolution *&ResI,
                       const SymbolResolution *ResE) {
+  const auto BMID = BM.getModuleIdentifier();
   const SymbolResolution *ResITmp = ResI;
   for (const InputFile::Symbol &Sym : Syms) {
     assert(ResITmp != ResE);
     SymbolResolution Res = *ResITmp++;
 
-    if (!Sym.getIRName().empty()) {
+    if (!Sym.getIRName().empty() && Res.Prevailing) {
       auto GUID = GlobalValue::getGUIDAssumingExternalLinkage(
           GlobalValue::getGlobalIdentifier(Sym.getIRName(),
                                            GlobalValue::ExternalLinkage, ""));
-      if (Res.Prevailing)
-        ThinLTO.PrevailingModuleForGUID[GUID] = BM.getModuleIdentifier();
+      ThinLTO.setPrevailingModuleForGUID(GUID, BMID);
     }
   }
 
-  if (Error Err =
-          BM.readSummary(ThinLTO.CombinedIndex, BM.getModuleIdentifier(),
-                         [&](GlobalValue::GUID GUID) {
-                           return ThinLTO.PrevailingModuleForGUID[GUID] ==
-                                  BM.getModuleIdentifier();
-                         }))
+  if (Error Err = BM.readSummary(
+          ThinLTO.CombinedIndex, BMID, [&](GlobalValue::GUID GUID) {
+            return ThinLTO.isPrevailingModuleForGUID(GUID, BMID);
+          }))
     return Err;
-  LLVM_DEBUG(dbgs() << "Module " << BM.getModuleIdentifier() << "\n");
+  LLVM_DEBUG(dbgs() << "Module " << BMID << "\n");
 
   for (const InputFile::Symbol &Sym : Syms) {
     assert(ResI != ResE);
     SymbolResolution Res = *ResI++;
 
-    if (!Sym.getIRName().empty()) {
+    if (!Sym.getIRName().empty() &&
+        (Res.Prevailing || Res.FinalDefinitionInLinkageUnit)) {
       auto GUID = GlobalValue::getGUIDAssumingExternalLinkage(
           GlobalValue::getGlobalIdentifier(Sym.getIRName(),
                                            GlobalValue::ExternalLinkage, ""));
       if (Res.Prevailing) {
-        assert(ThinLTO.PrevailingModuleForGUID[GUID] ==
-               BM.getModuleIdentifier());
+        assert(ThinLTO.isPrevailingModuleForGUID(GUID, BMID));
 
         // For linker redefined symbols (via --wrap or --defsym) we want to
         // switch the linkage to `weak` to prevent IPOs from happening.
         // Find the summary in the module for this very GV and record the new
         // linkage so that we can switch it when we import the GV.
         if (Res.LinkerRedefined)
-          if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(
-                  GUID, BM.getModuleIdentifier()))
+          if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(GUID, BMID))
             S->setLinkage(GlobalValue::WeakAnyLinkage);
       }
 
       // If the linker resolved the symbol to a local definition then mark it
       // as local in the summary for the module we are adding.
       if (Res.FinalDefinitionInLinkageUnit) {
-        if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(
-                GUID, BM.getModuleIdentifier())) {
+        if (auto S = ThinLTO.CombinedIndex.findSummaryInModule(GUID, BMID)) {
           S->setDSOLocal(true);
         }
       }
     }
   }
 
-  if (!ThinLTO.ModuleMap.insert({BM.getModuleIdentifier(), BM}).second)
+  if (!ThinLTO.ModuleMap.insert({BMID, BM}).second)
     return make_error<StringError>(
         "Expected at most one ThinLTO module per bitcode file",
         inconvertibleErrorCode());
@@ -1102,10 +1098,10 @@ Error LTO::addThinLTO(BitcodeModule BM, ArrayRef<InputFile::Symbol> Syms,
     // This is a fuzzy name matching where only modules with name containing the
     // specified switch values are going to be compiled.
     for (const std::string &Name : Conf.ThinLTOModulesToCompile) {
-      if (BM.getModuleIdentifier().contains(Name)) {
-        ThinLTO.ModulesToCompile->insert({BM.getModuleIdentifier(), BM});
-        LLVM_DEBUG(dbgs() << "[ThinLTO] Selecting " << BM.getModuleIdentifier()
-                          << " to compile\n");
+      if (BMID.contains(Name)) {
+        ThinLTO.ModulesToCompile->insert({BMID, BM});
+        LLVM_DEBUG(dbgs() << "[ThinLTO] Selecting " << BMID << " to compile\n");
+        break;
       }
     }
   }
@@ -1974,7 +1970,7 @@ Error LTO::runThinLTO(AddStreamFn AddStream, FileCache Cache,
                                LocalWPDTargetsMap);
 
   auto isPrevailing = [&](GlobalValue::GUID GUID, const GlobalValueSummary *S) {
-    return ThinLTO.PrevailingModuleForGUID[GUID] == S->modulePath();
+    return ThinLTO.isPrevailingModuleForGUID(GUID, S->modulePath());
   };
   if (EnableMemProfContextDisambiguation) {
     MemProfContextDisambiguation ContextDisambiguation;