diff --git a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
--- a/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ b/llvm/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -841,17 +841,35 @@
     std::vector<ValueInfo> &TargetsForSlot, const TypeIdCompatibleVtableInfo TIdInfo,
     uint64_t ByteOffset) {
   for (const TypeIdOffsetVtableInfo P : TIdInfo) {
-    // VTable initializer should have only one summary, or all copies must be
-    // linkonce/weak ODR.
+    // Ensure that we have at most one external linkage vtable initializer.
     assert(P.VTableVI.getSummaryList().size() == 1 ||
-           llvm::all_of(
+           llvm::count_if(
                P.VTableVI.getSummaryList(),
                [&](const std::unique_ptr<GlobalValueSummary> &Summary) {
-                 return GlobalValue::isLinkOnceODRLinkage(Summary->linkage()) ||
-                        GlobalValue::isWeakODRLinkage(Summary->linkage());
-               }));
-    const auto *VS = cast<GlobalVarSummary>(P.VTableVI.getSummaryList()[0].get());
-    if (!P.VTableVI.getSummaryList()[0]->isLive())
+                 return GlobalValue::isExternalLinkage(Summary->linkage());
+               }) <= 1);
+    // Find the first non-available_externally linkage vtable initializer.
+    // We can have multiple available_externally, linkonce_odr and weak_odr
+    // vtable initializers, however we want to skip available_externally as they
+    // do not have type metadata attached, and therefore the summary will not
+    // contain any vtable functions.
+    //
+    // Also, handle the case of same-named local Vtables with the same path
+    // and therefore the same GUID. This can happen if there isn't enough
+    // distinguishing path when compiling the source file. In that case we
+    // conservatively return false early.
+    const GlobalVarSummary *VS = nullptr;
+    bool LocalFound = false;
+    for (auto &S : P.VTableVI.getSummaryList()) {
+      if (GlobalValue::isLocalLinkage(S->linkage())) {
+        if (LocalFound)
+          return false;
+        LocalFound = true;
+      }
+      if (!GlobalValue::isAvailableExternallyLinkage(S->linkage()))
+        VS = cast<GlobalVarSummary>(S.get());
+    }
+    if (!VS->isLive())
       continue;
     for (auto VTP : VS->vTableFuncs()) {
       if (VTP.VTableOffset != P.AddressPointOffset + ByteOffset)
diff --git a/llvm/test/ThinLTO/X86/Inputs/devirt_available_externally.ll b/llvm/test/ThinLTO/X86/Inputs/devirt_available_externally.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/Inputs/devirt_available_externally.ll
@@ -0,0 +1,14 @@
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+%struct.D = type { i32 (...)** }
+
+@_ZTV1D = constant { [3 x i8*] } { [3 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.D*, i32)* @_ZN1D1mEi to i8*)] }, !type !3
+
+define i32 @_ZN1D1mEi(%struct.D* %this, i32 %a) #0 {
+   ret i32 0;
+}
+
+attributes #0 = { noinline optnone }
+
+!3 = !{i64 16, !"_ZTS1D"}
diff --git a/llvm/test/ThinLTO/X86/Inputs/devirt_local_same_guid.ll b/llvm/test/ThinLTO/X86/Inputs/devirt_local_same_guid.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/Inputs/devirt_local_same_guid.ll
@@ -0,0 +1,41 @@
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+source_filename = "-"
+
+%struct.A = type { i32 (...)** }
+%struct.B = type { %struct.A }
+
+@_ZTV1B = internal constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.B*, i32)* @_ZN1B1fEi to i8*), i8* bitcast (i32 (%struct.A*, i32)* @_ZN1A1nEi to i8*)] }, !type !0, !type !1
+
+define internal i32 @_ZN1B1fEi(%struct.B* %this, i32 %a) #0 {
+   ret i32 0;
+}
+
+define internal i32 @_ZN1A1nEi(%struct.A* %this, i32 %a) #0 {
+   ret i32 0;
+}
+
+define i32 @test2(%struct.B* %obj, i32 %a) {
+entry:
+  %0 = bitcast %struct.B* %obj to i8***
+  %vtable2 = load i8**, i8*** %0
+  %1 = bitcast i8** %vtable2 to i8*
+  %p2 = call i1 @llvm.type.test(i8* %1, metadata !"_ZTS1B")
+  call void @llvm.assume(i1 %p2)
+
+  %fptrptr = getelementptr i8*, i8** %vtable2, i32 1
+  %2 = bitcast i8** %fptrptr to i32 (%struct.B*, i32)**
+  %fptr33 = load i32 (%struct.B*, i32)*, i32 (%struct.B*, i32)** %2, align 8
+
+  %call4 = tail call i32 %fptr33(%struct.B* nonnull %obj, i32 %a)
+  ret i32 %call4
+}
+
+attributes #0 = { noinline optnone }
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1)
+
+!0 = !{i64 16, !"_ZTS1A"}
+!1 = !{i64 16, !"_ZTS1B"}
diff --git a/llvm/test/ThinLTO/X86/devirt_available_externally.ll b/llvm/test/ThinLTO/X86/devirt_available_externally.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/devirt_available_externally.ll
@@ -0,0 +1,72 @@
+; REQUIRES: x86-registered-target
+
+; Test index-based devirtualization when first copy is available_externally,
+; which doesn't have type metadata. We should use the strong external
+; def in the other module to devirtualize.
+
+; Generate unsplit module with summary for ThinLTO index-based WPD.
+; RUN: opt -thinlto-bc -o %t3.o %s
+; RUN: opt -thinlto-bc -o %t4.o %p/Inputs/devirt_available_externally.ll
+
+; The available_externally copy should not get vTableFuncs information in its
+; summary entry, but the external def should.
+; RUN: llvm-dis -o - %t3.o | FileCheck %s --check-prefix=AVAILEXTERNAL
+; AVAILEXTERNAL: gv: (name: "_ZTV1D"
+; AVAILEXTERNAL-NOT: vTableFuncs
+; AVAILEXTERNAL-SAME: ; guid =
+; RUN: llvm-dis -o - %t4.o | FileCheck %s --check-prefix=EXTERNAL
+; EXTERNAL: gv: (name: "_ZTV1D", {{.*}} vTableFuncs: ((virtFunc:
+
+; RUN: llvm-lto2 run %t3.o %t4.o -save-temps -pass-remarks=. \
+; RUN:   -wholeprogramdevirt-print-index-based \
+; RUN:   -o %t5 \
+; RUN:   -r=%t3.o,test,px \
+; RUN:   -r=%t3.o,_ZTV1D, \
+; RUN:   -r=%t3.o,_ZN1D1mEi, \
+; RUN:   -r=%t4.o,_ZN1D1mEi,p \
+; RUN:   -r=%t4.o,_ZTV1D,px \
+; RUN:   2>&1 | FileCheck %s --check-prefix=REMARK --check-prefix=PRINT
+; RUN: llvm-dis %t5.1.4.opt.bc -o - | FileCheck %s --check-prefix=CHECK-IR1
+; RUN: llvm-nm %t5.1 | FileCheck %s --check-prefix=NM-INDEX1
+; RUN: llvm-nm %t5.2 | FileCheck %s --check-prefix=NM-INDEX2
+
+; NM-INDEX1-DAG: U _ZN1D1mEi
+
+; NM-INDEX2-DAG: T _ZN1D1mEi
+
+; PRINT-DAG: Devirtualized call to {{.*}} (_ZN1D1mEi)
+
+; REMARK-DAG: single-impl: devirtualized a call to _ZN1D1mEi
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+%struct.D = type { i32 (...)** }
+
+@_ZTV1D = available_externally constant { [3 x i8*] } { [3 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.D*, i32)* @_ZN1D1mEi to i8*)] }
+
+; CHECK-IR1-LABEL: define i32 @test
+define i32 @test(%struct.D* %obj2, i32 %a) {
+entry:
+  %0 = bitcast %struct.D* %obj2 to i8***
+  %vtable2 = load i8**, i8*** %0
+  %1 = bitcast i8** %vtable2 to i8*
+  %p2 = call i1 @llvm.type.test(i8* %1, metadata !"_ZTS1D")
+  call void @llvm.assume(i1 %p2)
+
+  %2 = bitcast i8** %vtable2 to i32 (%struct.D*, i32)**
+  %fptr33 = load i32 (%struct.D*, i32)*, i32 (%struct.D*, i32)** %2, align 8
+
+  ; Check that the call was devirtualized.
+  ; CHECK-IR1: %call4 = tail call i32 @_ZN1D1mEi
+  %call4 = tail call i32 %fptr33(%struct.D* nonnull %obj2, i32 %a)
+  ret i32 %call4
+}
+; CHECK-IR1-LABEL: ret i32
+; CHECK-IR1-LABEL: }
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1)
+declare i32 @_ZN1D1mEi(%struct.D* %this, i32 %a)
+
+attributes #0 = { noinline optnone }
diff --git a/llvm/test/ThinLTO/X86/devirt_local_same_guid.ll b/llvm/test/ThinLTO/X86/devirt_local_same_guid.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/ThinLTO/X86/devirt_local_same_guid.ll
@@ -0,0 +1,74 @@
+; REQUIRES: x86-registered-target
+
+; Test that index-based devirtualization in the presence of same-named
+; local vtables in same named source files fails.
+
+; Generate unsplit module with summary for ThinLTO index-based WPD.
+; RUN: opt -thinlto-bc -o %t3.o %s
+; RUN: opt -thinlto-bc -o %t4.o %p/Inputs/devirt_local_same_guid.ll
+
+; RUN: llvm-lto2 run %t3.o %t4.o -save-temps -use-new-pm -pass-remarks=. \
+; RUN:   -wholeprogramdevirt-print-index-based \
+; RUN:   -o %t5 \
+; RUN:   -r=%t3.o,use_B,px \
+; RUN:   -r=%t3.o,test,px \
+; RUN:   -r=%t4.o,test2,px
+; RUN: llvm-dis %t5.1.4.opt.bc -o - | FileCheck %s --check-prefix=CHECK-IR1
+; RUN: llvm-dis %t5.2.4.opt.bc -o - | FileCheck %s --check-prefix=CHECK-IR2
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+source_filename = "-"
+
+%struct.A = type { i32 (...)** }
+%struct.B = type { %struct.A }
+
+@_ZTV1B = internal constant { [4 x i8*] } { [4 x i8*] [i8* null, i8* undef, i8* bitcast (i32 (%struct.B*, i32)* @_ZN1B1fEi to i8*), i8* bitcast (i32 (%struct.B*, i32)* @_ZN1B1nEi to i8*)] }, !type !0, !type !1
+
+define internal i32 @_ZN1B1fEi(%struct.B* %this, i32 %a) #0 {
+   ret i32 0;
+}
+
+define internal i32 @_ZN1B1nEi(%struct.B* %this, i32 %a) #0 {
+   ret i32 0;
+}
+
+; Ensures that vtable of B is live so that we will attempt devirt.
+define dso_local i32 @use_B(%struct.B* %a) {
+entry:
+  %0 = bitcast %struct.B* %a to i32 (...)***
+  store i32 (...)** bitcast (i8** getelementptr inbounds ({ [4 x i8*] }, { [4 x i8*] }* @_ZTV1B, i64 0, inrange i32 0, i64 2) to i32 (...)**), i32 (...)*** %0, align 8
+  ret i32 0
+}
+
+; CHECK-IR1: define i32 @test(
+define i32 @test(%struct.A* %obj, i32 %a) {
+entry:
+  %0 = bitcast %struct.A* %obj to i8***
+  %vtable = load i8**, i8*** %0
+  %1 = bitcast i8** %vtable to i8*
+  %p = call i1 @llvm.type.test(i8* %1, metadata !"_ZTS1A")
+  call void @llvm.assume(i1 %p)
+  %fptrptr = getelementptr i8*, i8** %vtable, i32 1
+  %2 = bitcast i8** %fptrptr to i32 (%struct.A*, i32)**
+  %fptr1 = load i32 (%struct.A*, i32)*, i32 (%struct.A*, i32)** %2, align 8
+
+  ; Check that the call was not devirtualized.
+  ; CHECK-IR1: %call = tail call i32 %fptr1
+  %call = tail call i32 %fptr1(%struct.A* nonnull %obj, i32 %a)
+
+  ret i32 %call
+}
+
+; CHECK-IR2: define i32 @test2
+; Check that the call was not devirtualized.
+; CHECK-IR2:   %call4 = tail call i32 %fptr
+
+declare i1 @llvm.type.test(i8*, metadata)
+declare void @llvm.assume(i1)
+
+attributes #0 = { noinline optnone }
+
+!0 = !{i64 16, !"_ZTS1A"}
+!1 = !{i64 16, !"_ZTS1B"}