3 files changed, 28 insertions, 8 deletions
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index dd9d6305caa..8175347f95c 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1372,6 +1372,15 @@ void CodeGenModule::EmitGlobal(GlobalDecl GD) {
                               /*DontDefer=*/false);
       return;
     }
+
+    if (llvm::GlobalValue *GV = GetGlobalValue(getMangledName(GD)))
+      if (!GV->isDeclaration()) {
+        getDiags().Report(FD->getLocation(), diag::err_duplicate_mangled_name);
+        GlobalDecl OldGD = Manglings.lookup(GV->getName());
+        if (auto *Prev = OldGD.getDecl())
+          getDiags().Report(Prev->getLocation(), diag::note_previous_definition);
+        return;
+      }
   } else {
     const auto *VD = cast<VarDecl>(Global);
     assert(VD->isFileVarDecl() && "Cannot emit local var decl as global.");
@@ -2405,14 +2414,6 @@ void CodeGenModule::EmitGlobalFunctionDefinition(GlobalDecl GD,
     }
   }
 
-  if (!GV->isDeclaration()) {
-    getDiags().Report(D->getLocation(), diag::err_duplicate_mangled_name);
-    GlobalDecl OldGD = Manglings.lookup(GV->getName());
-    if (auto *Prev = OldGD.getDecl())
-      getDiags().Report(Prev->getLocation(), diag::note_previous_definition);
-    return;
-  }
-
   if (GV->getType()->getElementType() != Ty) {
     // If the types mismatch then we have to rewrite the definition.
     assert(GV->isDeclaration() && "Shouldn't replace non-declaration");
diff --git a/clang/test/CodeGenCXX/duplicate-mangled-name2.cpp b/clang/test/CodeGenCXX/duplicate-mangled-name2.cpp
new file mode 100644
index 00000000000..e582733fd8a
--- /dev/null
+++ b/clang/test/CodeGenCXX/duplicate-mangled-name2.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu -emit-llvm-only %s -verify
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu -femit-all-decls -emit-llvm-only %s -verify
+
+void foo(void *p) __asm("_ZN1SC2Ev");
+void foo(void *p) { } // expected-note {{previous}}
+
+struct S {
+  S() {} // expected-error {{definition with same mangled name as another definition}}
+} s;
diff --git a/clang/test/CodeGenCXX/duplicate-mangled-name3.cpp b/clang/test/CodeGenCXX/duplicate-mangled-name3.cpp
new file mode 100644
index 00000000000..17dbc9bc85f
--- /dev/null
+++ b/clang/test/CodeGenCXX/duplicate-mangled-name3.cpp
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -emit-llvm-only %s -verify
+// RUN: %clang_cc1 -triple %itanium_abi_triple -femit-all-decls -emit-llvm-only %s -verify
+
+extern "C" {
+  void _ZN1SC2Ev(void *p) { } // expected-note {{previous}}
+}
+
+struct S {
+  S() {} // expected-error {{definition with same mangled name as another definition}}
+} s;