Index: include/llvm/IR/ModuleSummaryIndex.h
===================================================================
--- include/llvm/IR/ModuleSummaryIndex.h
+++ include/llvm/IR/ModuleSummaryIndex.h
@@ -104,11 +104,23 @@
     /// Indicate if the global value is located in a specific section.
     unsigned HasSection : 1;
 
+    /// Indicate if the function is not viable to inline.
+    unsigned IsNotViableToInline : 1;
+
     /// Convenience Constructors
-    explicit GVFlags(GlobalValue::LinkageTypes Linkage, bool HasSection)
-        : Linkage(Linkage), HasSection(HasSection) {}
+    explicit GVFlags(GlobalValue::LinkageTypes Linkage, bool HasSection,
+                     bool IsNotViableToInline)
+        : Linkage(Linkage), HasSection(HasSection),
+          IsNotViableToInline(IsNotViableToInline) {}
+
     GVFlags(const GlobalValue &GV)
-        : Linkage(GV.getLinkage()), HasSection(GV.hasSection()) {}
+        : Linkage(GV.getLinkage()), HasSection(GV.hasSection()) {
+      IsNotViableToInline = false;
+      if (const auto *F = dyn_cast<Function>(&GV))
+        // Inliner doesn't handle variadic functions.
+        // FIXME: refactor this to use the same code that inliner is using.
+        IsNotViableToInline = F->isVarArg();
+    }
   };
 
 private:
@@ -175,6 +187,8 @@
     Flags.Linkage = Linkage;
   }
 
+  bool isNotViableToInline() const { return Flags.IsNotViableToInline; }
+
   /// Return true if this summary is for a GlobalValue that needs promotion
   /// to be referenced from another module.
   bool needsRenaming() const { return GlobalValue::isLocalLinkage(linkage()); }
Index: lib/Bitcode/Reader/BitcodeReader.cpp
===================================================================
--- lib/Bitcode/Reader/BitcodeReader.cpp
+++ lib/Bitcode/Reader/BitcodeReader.cpp
@@ -720,7 +720,7 @@
   }
 }
 
-// Decode the flags for GlobalValue in the summary
+/// Decode the flags for GlobalValue in the summary.
 static GlobalValueSummary::GVFlags getDecodedGVSummaryFlags(uint64_t RawFlags,
                                                             uint64_t Version) {
   // Summary were not emitted before LLVM 3.9, we don't need to upgrade Linkage
@@ -728,8 +728,9 @@
   // to getDecodedLinkage() will need to be taken into account here as above.
   auto Linkage = GlobalValue::LinkageTypes(RawFlags & 0xF); // 4 bits
   RawFlags = RawFlags >> 4;
-  auto HasSection = RawFlags & 0x1; // bool
-  return GlobalValueSummary::GVFlags(Linkage, HasSection);
+  bool HasSection = RawFlags & 0x1;
+  bool IsNotViableToInline = RawFlags & 0x2;
+  return GlobalValueSummary::GVFlags(Linkage, HasSection, IsNotViableToInline);
 }
 
 static GlobalValue::VisibilityTypes getDecodedVisibility(unsigned Val) {
Index: lib/Bitcode/Writer/BitcodeWriter.cpp
===================================================================
--- lib/Bitcode/Writer/BitcodeWriter.cpp
+++ lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -991,7 +991,7 @@
   uint64_t RawFlags = 0;
 
   RawFlags |= Flags.HasSection; // bool
-
+  RawFlags |= (Flags.IsNotViableToInline << 1);
   // Linkage don't need to be remapped at that time for the summary. Any future
   // change to the getEncodedLinkage() function will need to be taken into
   // account here as well.
Index: lib/Transforms/IPO/FunctionImport.cpp
===================================================================
--- lib/Transforms/IPO/FunctionImport.cpp
+++ lib/Transforms/IPO/FunctionImport.cpp
@@ -130,6 +130,10 @@
     // FIXME: we may be able to import it by copying it without promotion.
     return false;
 
+  // Don't import functions that are not viable to inline.
+  if (Summary.isNotViableToInline())
+    return false;
+
   // Check references (and potential calls) in the same module. If the current
   // value references a global that can't be externally referenced it is not
   // eligible for import.
Index: test/Bitcode/thinlto-function-summary.ll
===================================================================
--- test/Bitcode/thinlto-function-summary.ll
+++ test/Bitcode/thinlto-function-summary.ll
@@ -9,13 +9,17 @@
 ; BC-NEXT: <PERMODULE {{.*}} op0=1 op1=0
 ; BC-NEXT: <PERMODULE {{.*}} op0=2 op1=0
 ; BC-NEXT: <PERMODULE {{.*}} op0=3 op1=7
-; BC-NEXT: <ALIAS {{.*}} op0=4 op1=0 op2=3
+; BC-NEXT: <PERMODULE {{.*}} op0=4 op1=32
+; BC-NEXT: <ALIAS {{.*}} op0=5 op1=0 op2=3
 ; BC-NEXT: </GLOBALVAL_SUMMARY_BLOCK
 ; BC-NEXT: <VALUE_SYMTAB
-; BC-NEXT: <FNENTRY {{.*}} op0=3 {{.*}}> record string = 'anon.
+; BC-NEXT: <FNENTRY {{.*}} op0=4 {{.*}}> record string = 'variadic'
 ; BC-NEXT: <FNENTRY {{.*}} op0=1 {{.*}}> record string = 'foo'
 ; BC-NEXT: <FNENTRY {{.*}} op0=2 {{.*}}> record string = 'bar'
-; BC-NEXT: <FNENTRY {{.*}} op0=4 {{.*}}> record string = 'f'
+; BC-NEXT: <FNENTRY {{.*}} op0=5 {{.*}}> record string = 'f'
+; BC-NEXT: <ENTRY {{.*}} record string = 'h'
+; BC-NEXT: <FNENTRY {{.*}} op0=3 {{.*}}> record string = 'anon.
+
 
 ; RUN: opt -name-anon-functions -module-summary < %s | llvm-dis | FileCheck %s
 ; Check that this round-trips correctly.
@@ -56,3 +60,7 @@
 return:         ; preds = %entry
         ret void
 }
+
+define i32 @variadic(...) {
+    ret i32 42
+}
Index: test/Transforms/FunctionImport/Inputs/funcimport.ll
===================================================================
--- test/Transforms/FunctionImport/Inputs/funcimport.ll
+++ test/Transforms/FunctionImport/Inputs/funcimport.ll
@@ -11,6 +11,7 @@
 define void @globalfunc1() #0 {
 entry:
   call void @funcwithpersonality()
+  call void (...) @variadic()
   ret void
 }
 
@@ -146,4 +147,8 @@
   ret void
 }
 
+; Variadic function should not be imported because inliner doesn't handle it.
+define void @variadic(...) {
+    ret void
+}
 
Index: test/Transforms/FunctionImport/funcimport.ll
===================================================================
--- test/Transforms/FunctionImport/funcimport.ll
+++ test/Transforms/FunctionImport/funcimport.ll
@@ -32,6 +32,7 @@
   call void (...) @weakfunc()
   call void (...) @linkoncefunc2()
   call void (...) @referencelargelinkonce()
+  call void (...) @variadic()
   ret i32 0
 }
 
@@ -105,6 +106,9 @@
 ; INSTLIMDEF-DAG: define available_externally hidden void @funcwithpersonality.llvm.{{.*}}() personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) !thinlto_src_module !0 {
 ; INSTLIM5-DAG: declare hidden void @funcwithpersonality.llvm.{{.*}}()
 
+; CHECK-DAG: declare void @variadic(...)
+declare void @variadic(...)
+
 ; INSTLIMDEF-DAG: Import globalfunc2
 ; INSTLIMDEF-DAG: 13 function-import - Number of functions imported
 ; CHECK-DAG: !0 = !{!"{{.*}}/Inputs/funcimport.ll"}