diff --git a/llvm/include/llvm/IR/ModuleSummaryIndex.h b/llvm/include/llvm/IR/ModuleSummaryIndex.h
--- a/llvm/include/llvm/IR/ModuleSummaryIndex.h
+++ b/llvm/include/llvm/IR/ModuleSummaryIndex.h
@@ -228,7 +228,9 @@
   /// protected and hidden.
   GlobalValue::VisibilityTypes getELFVisibility() const;
 
-  bool isDSOLocal() const;
+  /// Checks if all summaries are DSO local (have the flag set). When DSOLocal
+  /// propagation has been done, set the parameter to enable fast check.
+  bool isDSOLocal(bool WithDSOLocalPropagation = false) const;
 
   /// Checks if all copies are eligible for auto-hiding (have flag set).
   bool canAutoHide() const;
@@ -1055,6 +1057,10 @@
   /// read/write only.
   bool WithAttributePropagation = false;
 
+  /// Indicates that summary-based DSOLocal propagation has run and the flag in
+  /// every summary of a GV is synchronized.
+  bool WithDSOLocalPropagation = false;
+
   /// Indicates that summary-based synthetic entry count propagation has run
   bool HasSyntheticEntryCounts = false;
 
@@ -1210,6 +1216,9 @@
     WithAttributePropagation = true;
   }
 
+  bool withDSOLocalPropagation() const { return WithDSOLocalPropagation; }
+  void setWithDSOLocalPropagation() { WithDSOLocalPropagation = true; }
+
   bool isReadOnly(const GlobalVarSummary *GVS) const {
     return WithAttributePropagation && GVS->maybeReadOnly();
   }
diff --git a/llvm/lib/IR/ModuleSummaryIndex.cpp b/llvm/lib/IR/ModuleSummaryIndex.cpp
--- a/llvm/lib/IR/ModuleSummaryIndex.cpp
+++ b/llvm/lib/IR/ModuleSummaryIndex.cpp
@@ -52,13 +52,17 @@
                       : GlobalValue::DefaultVisibility;
 }
 
-bool ValueInfo::isDSOLocal() const {
-  // Need to check all summaries are local in case of hash collisions.
-  return getSummaryList().size() &&
-         llvm::all_of(getSummaryList(),
-                      [](const std::unique_ptr<GlobalValueSummary> &Summary) {
-                        return Summary->isDSOLocal();
-                      });
+bool ValueInfo::isDSOLocal(bool WithDSOLocalPropagation) const {
+  // With DSOLocal propagation done, the flag in evey summary is the same.
+  // Check the first one is enough.
+  return WithDSOLocalPropagation
+             ? getSummaryList().size() && getSummaryList()[0]->isDSOLocal()
+             : getSummaryList().size() &&
+                   llvm::all_of(
+                       getSummaryList(),
+                       [](const std::unique_ptr<GlobalValueSummary> &Summary) {
+                         return Summary->isDSOLocal();
+                       });
 }
 
 bool ValueInfo::canAutoHide() const {
@@ -205,7 +209,7 @@
   }
 }
 
-// Do the access attribute propagation in combined index.
+// Do the access attribute and DSOLocal propagation in combined index.
 // The goal of attribute propagation is internalization of readonly (RO)
 // or writeonly (WO) variables. To determine which variables are RO or WO
 // and which are not we take following steps:
@@ -216,7 +220,7 @@
 //   or doesn't read it (writeonly).
 //
 // - After computing dead symbols in combined index we do the attribute
-//   propagation. During this step we:
+//   and DSOLocal propagation. During this step we:
 //   a. clear RO and WO attributes from variables which are preserved or
 //      can't be imported
 //   b. clear RO and WO attributes from variables referenced by any global
@@ -225,6 +229,7 @@
 //      reference is not readonly
 //   d. clear WO attribute from variable referenced by a function when
 //      reference is not writeonly
+//   e. clear IsDSOLocal flag in every summary if any of them is false.
 //
 //   Because of (c, d) we don't internalize variables read by function A
 //   and modified by function B.
@@ -236,7 +241,8 @@
   if (!PropagateAttrs)
     return;
   DenseSet<ValueInfo> MarkedNonReadWriteOnly;
-  for (auto &P : *this)
+  for (auto &P : *this) {
+    bool IsDSOLocal = true;
     for (auto &S : P.second.SummaryList) {
       if (!isGlobalValueLive(S.get())) {
         // computeDeadSymbols should have marked all copies live. Note that
@@ -273,8 +279,20 @@
           GVS->setWriteOnly(false);
         }
       propagateAttributesToRefs(S.get(), MarkedNonReadWriteOnly);
+
+      // If the flag from any summary is false, the GV is not DSOLocal.
+      IsDSOLocal &= S->isDSOLocal();
     }
+    if (!IsDSOLocal)
+      // Mark the flag in all summaries false so that we can do quick check
+      // without going through the whole list.
+      llvm::for_each(P.second.SummaryList,
+                     [](const std::unique_ptr<GlobalValueSummary> &Summary) {
+                       return Summary->setDSOLocal(false);
+                     });
+  }
   setWithAttributePropagation();
+  setWithDSOLocalPropagation();
   if (llvm::AreStatisticsEnabled())
     for (auto &P : *this)
       if (P.second.SummaryList.size())
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -207,7 +207,7 @@
     AddUnsigned(GS->isLive());
     AddUnsigned(GS->canAutoHide());
     for (const ValueInfo &VI : GS->refs()) {
-      AddUnsigned(VI.isDSOLocal());
+      AddUnsigned(VI.isDSOLocal(Index.withDSOLocalPropagation()));
       AddUsedCfiGlobal(VI.getGUID());
     }
     if (auto *GVS = dyn_cast<GlobalVarSummary>(GS)) {
@@ -226,7 +226,7 @@
       for (auto &TT : FS->type_checked_load_const_vcalls())
         UsedTypeIds.insert(TT.VFunc.GUID);
       for (auto &ET : FS->calls()) {
-        AddUnsigned(ET.first.isDSOLocal());
+        AddUnsigned(ET.first.isDSOLocal(Index.withDSOLocalPropagation()));
         AddUsedCfiGlobal(ET.first.getGUID());
       }
     }
diff --git a/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp b/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
--- a/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
+++ b/llvm/lib/Transforms/Utils/FunctionImportUtils.cpp
@@ -279,7 +279,7 @@
   if (ClearDSOLocalOnDeclarations && GV.isDeclarationForLinker() &&
       !GV.isImplicitDSOLocal()) {
     GV.setDSOLocal(false);
-  } else if (VI && VI.isDSOLocal()) {
+  } else if (VI && VI.isDSOLocal(ImportIndex.withDSOLocalPropagation())) {
     // If all summaries are dso_local, symbol gets resolved to a known local
     // definition.
     GV.setDSOLocal(true);