diff --git a/clang/lib/CodeGen/CGVTables.h b/clang/lib/CodeGen/CGVTables.h
--- a/clang/lib/CodeGen/CGVTables.h
+++ b/clang/lib/CodeGen/CGVTables.h
@@ -154,6 +154,10 @@
   /// when a vtable may not be dso_local.
   void GenerateRelativeVTableAlias(llvm::GlobalVariable *VTable,
                                    llvm::StringRef AliasNameRef);
+
+  /// Check if we can place the vtable in a comdat group under the relative
+  /// layout.
+  bool CanPlaceRelativeVTableInComdat(const llvm::GlobalVariable *VTable);
 };
 
 } // end namespace CodeGen
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -936,9 +936,19 @@
   if (UsingRelativeLayout && !VTable->isDSOLocal())
     GenerateRelativeVTableAlias(VTable, OutName);
 
+  if (CanPlaceRelativeVTableInComdat(VTable))
+    VTable->setComdat(CGM.getModule().getOrInsertComdat(VTable->getName()));
+
   return VTable;
 }
 
+bool CodeGenVTables::CanPlaceRelativeVTableInComdat(
+    const llvm::GlobalVariable *VTable) {
+  return CGM.supportsCOMDAT() && getItaniumVTableContext().isRelativeLayout() &&
+         !VTable->hasLocalLinkage() && !VTable->isDeclarationForLinker() &&
+         !VTable->hasComdat();
+}
+
 // If the VTable is not dso_local, then we will not be able to indicate that
 // the VTable does not need a relocation and move into rodata. A frequent
 // time this can occur is for classes that should be made public from a DSO
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -1772,6 +1772,9 @@
 
   if (VTContext.isRelativeLayout() && !VTable->isDSOLocal())
     CGVT.GenerateRelativeVTableAlias(VTable, VTable->getName());
+
+  if (CGVT.CanPlaceRelativeVTableInComdat(VTable))
+    VTable->setComdat(CGM.getModule().getOrInsertComdat(VTable->getName()));
 }
 
 bool ItaniumCXXABI::isVirtualOffsetNeededForVTableField(
diff --git a/clang/test/CodeGenCXX/RelativeVTablesABI/vtable-in-comdat.cpp b/clang/test/CodeGenCXX/RelativeVTablesABI/vtable-in-comdat.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenCXX/RelativeVTablesABI/vtable-in-comdat.cpp
@@ -0,0 +1,24 @@
+// Check that all vtables under the relative ABI are placed in a comdat group.
+// This is necessary because if the vtable happens to fit in a mergable
+// constants section, then the LLVM backend will not place the symbol in its own
+// unique section even if -fdata-sections is enabled. (That is, in the object
+// file the vtable is defined, it will be in section .rodata.cst{N} instead of
+// something like .rodata.{vtable}). This can cause vtables to be retained that
+// normally would be collected by --gc-sections. Placing them in a comdat group
+// can guarantee that they will be placed in a unique section group and garbage
+// collected.
+
+// RUN: %clang_cc1 %s -triple=aarch64-unknown-fuchsia -S -o - -emit-llvm -fexperimental-relative-c++-abi-vtables -fno-rtti | FileCheck %s
+
+// This will result in a vtable of size 16, which would normally be placed in
+// .rodata.cst16.
+class A {
+public:
+  virtual void func();
+  virtual void func2();
+};
+
+void A::func() {}
+void A::func2() {}
+
+// CHECK: @_ZTV1A = {{.*}}, comdat, align 4