Index: lib/AST/VTableBuilder.cpp
===================================================================
--- lib/AST/VTableBuilder.cpp
+++ lib/AST/VTableBuilder.cpp
@@ -411,7 +411,8 @@
   for (const auto *MD : RD->methods()) {
     if (!MD->isVirtual())
       continue;
-  
+    MD = MD->getCanonicalDecl();
+
     OverriderInfo Overrider = getOverrider(MD, Base.getBaseOffset());
 
     Out << "  ";
@@ -695,6 +696,7 @@
   for (const auto *MD : RD->methods()) {
     if (!MD->isVirtual())
       continue;
+    MD = MD->getCanonicalDecl();
 
     CharUnits OffsetOffset = getCurrentOffsetOffset();
     
@@ -1514,6 +1516,7 @@
   for (const auto *MD : RD->methods()) {
     if (!MD->isVirtual())
       continue;
+    MD = MD->getCanonicalDecl();
 
     // Get the final overrider.
     FinalOverriders::OverriderInfo Overrider = 
@@ -2196,6 +2199,7 @@
     // We only want virtual member functions.
     if (!MD->isVirtual())
       continue;
+    MD = MD->getCanonicalDecl();
 
     std::string MethodName =
       PredefinedExpr::ComputeName(PredefinedExpr::PrettyFunctionNoVirtual,
Index: test/Modules/Inputs/merge-vtable-codegen/a.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/merge-vtable-codegen/a.h
@@ -0,0 +1,8 @@
+#ifndef A_H
+#define A_H
+
+struct A {
+  virtual void x();
+};
+
+#endif
Index: test/Modules/Inputs/merge-vtable-codegen/b.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/merge-vtable-codegen/b.h
@@ -0,0 +1,17 @@
+#ifndef B_H
+#define B_H
+
+#include "a.h"
+
+class B : virtual public A {
+  virtual void x() {}
+};
+
+void b(A* p) {
+  p->x();
+  // Instantiating a class that virtually inherits 'A'
+  // triggers calculation of the vtable offsets in 'A'.
+  B b;
+}
+
+#endif
Index: test/Modules/Inputs/merge-vtable-codegen/c.h
===================================================================
--- /dev/null
+++ test/Modules/Inputs/merge-vtable-codegen/c.h
@@ -0,0 +1,6 @@
+#ifndef C_H
+#define C_H
+
+#include "a.h"
+
+#endif
Index: test/Modules/Inputs/merge-vtable-codegen/merge-vtable-codegen.modulemap
===================================================================
--- /dev/null
+++ test/Modules/Inputs/merge-vtable-codegen/merge-vtable-codegen.modulemap
@@ -0,0 +1,11 @@
+module "a" {
+  textual header "a.h"
+}
+
+module "b" {
+  header "b.h"
+}
+
+module "c" {
+  header "c.h"
+}
Index: test/Modules/merge-vtable-codegen.cpp
===================================================================
--- /dev/null
+++ test/Modules/merge-vtable-codegen.cpp
@@ -0,0 +1,24 @@
+// RUN: rm -rf %t
+
+// First, build two modules that both re-export the same header.
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fmodule-name=b -o %t/b.pcm -fmodule-maps \
+// RUN:     -emit-module %S/Inputs/merge-vtable-codegen/merge-vtable-codegen.modulemap \
+// RUN:     -I %S/Inputs/merge-vtable-codegen
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fmodule-name=c -o %t/c.pcm -fmodule-maps \
+// RUN:     -emit-module %S/Inputs/merge-vtable-codegen/merge-vtable-codegen.modulemap \
+// RUN:     -I %S/Inputs/merge-vtable-codegen
+
+// Use the two modules in a single compile.
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fmodule-file=%t/b.pcm -fmodule-file=%t/c.pcm \
+// RUN:     -fmodule-map-file=%S/Inputs/merge-vtable-codegen/merge-vtable-codegen.modulemap \
+// RUN:     -emit-llvm -o %t/test.o %s
+
+// Note that order is important:
+// Module 'c' just reexports A, while module 'b' defines a method that uses a
+// virtual method of A.
+#include "Inputs/merge-vtable-codegen/c.h"
+#include "Inputs/merge-vtable-codegen/b.h"
+
+void t() {
+  b(nullptr);
+}