Index: llvm/lib/IR/Function.cpp
===================================================================
--- llvm/lib/IR/Function.cpp
+++ llvm/lib/IR/Function.cpp
@@ -1658,11 +1658,26 @@
 
   Intrinsic::ID ID = F->getIntrinsicID();
   StringRef Name = F->getName();
-  if (Name ==
-      Intrinsic::getName(ID, ArgTys, F->getParent(), F->getFunctionType()))
+  std::string WantedName =
+      Intrinsic::getName(ID, ArgTys, F->getParent(), F->getFunctionType());
+  if (Name == WantedName)
     return None;
 
-  auto NewDecl = Intrinsic::getDeclaration(F->getParent(), ID, ArgTys);
+  GlobalValue *ExistingF = F->getParent()->getNamedValue(WantedName);
+
+  Function *NewDecl = nullptr;
+  if (ExistingF) {
+    if (cast<Function>(ExistingF)->getFunctionType() == F->getFunctionType()) {
+      NewDecl = cast<Function>(ExistingF);
+    } else {
+      // The name already exists, but has the wrong prototype. Make place for
+      // the new one by renaming the old version.
+      ExistingF->setName(Name + ".renamed");
+    }
+  }
+
+  if (!NewDecl)
+    NewDecl = Intrinsic::getDeclaration(F->getParent(), ID, ArgTys);
   NewDecl->setCallingConv(F->getCallingConv());
   assert(NewDecl->getFunctionType() == F->getFunctionType() &&
          "Shouldn't change the signature");
Index: llvm/test/tools/llvm-link/Inputs/remangle1.ll
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-link/Inputs/remangle1.ll
@@ -0,0 +1,10 @@
+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-unknown-linux-gnu"
+
+%aaa = type <{ %aab, i32, [4 x i8] }>
+%aab = type { i64 }
+%fum = type { %aac, i8, [7 x i8] }
+%aac = type { [8 x i8] }
+
+declare void @bar01(%aaa*)
+declare void @bar02(%fum*)
Index: llvm/test/tools/llvm-link/Inputs/remangle2.ll
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-link/Inputs/remangle2.ll
@@ -0,0 +1,27 @@
+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-unknown-linux-gnu"
+
+%fum = type { %aab, i8, [7 x i8] }
+%aab = type { %aba }
+%aba = type { [8 x i8] }
+%fum.1 = type { %abb, i8, [7 x i8] }
+%abb = type { %abc }
+%abc = type { [4 x i8] }
+
+declare void @foo(%fum*)
+
+declare %fum.1** @"llvm.ssa.copy.p0p0s_fum.1s"(%fum.1**)
+
+declare %fum** @"llvm.ssa.copy.p0p0s_fums"(%fum**)
+
+define void @foo1(%fum** %a, %fum.1 ** %b) {
+  %b.copy = call %fum.1** @"llvm.ssa.copy.p0p0s_fum.1s"(%fum.1** %b)
+  %a.copy = call %fum** @"llvm.ssa.copy.p0p0s_fums"(%fum** %a)
+  ret void
+}
+
+define void @foo2(%fum.1 ** %b, %fum** %a) {
+  %a.copy = call %fum** @"llvm.ssa.copy.p0p0s_fums"(%fum** %a)
+  %b.copy = call %fum.1** @"llvm.ssa.copy.p0p0s_fum.1s"(%fum.1** %b)
+  ret void
+}
Index: llvm/test/tools/llvm-link/remangle.ll
===================================================================
--- /dev/null
+++ llvm/test/tools/llvm-link/remangle.ll
@@ -0,0 +1,27 @@
+# RUN: llvm-as %S/Inputs/remangle1.ll -o %t.remangle1.bc
+# RUN: llvm-as %S/Inputs/remangle2.ll -o %t.remangle2.bc
+# RUN: llvm-link %t.remangle1.bc %t.remangle2.bc -o %t.remangle.linked.bc
+# RUN: llvm-dis %t.remangle.linked.bc -o - | FileCheck %s
+
+; CHECK-DAG: %fum.1 = type { %aab.0, i8, [7 x i8] }
+; CHECK-DAG: %aab.0 = type { %aba }
+; CHECK-DAG: %aba = type { [8 x i8] }
+; CHECK-DAG: %fum.1.2 = type { %abb, i8, [7 x i8] }
+; CHECK-DAG: %abb = type { %abc }
+; CHECK-DAG: %abc = type { [4 x i8] }
+
+; CHECK-LABEL: define void @foo1(%fum.1** %a, %fum.1.2** %b) {
+; CHECK-NEXT:   %b.copy = call %fum.1.2** @llvm.ssa.copy.p0p0s_fum.1.2s(%fum.1.2** %b)
+; CHECK-NEXT:   %a.copy = call %fum.1** @llvm.ssa.copy.p0p0s_fum.1s(%fum.1** %a)
+; CHECK-NEXT:  ret void
+
+; CHECK: declare %fum.1.2** @llvm.ssa.copy.p0p0s_fum.1.2s(%fum.1.2** returned)
+
+; CHECK: declare %fum.1** @llvm.ssa.copy.p0p0s_fum.1s(%fum.1** returned)
+
+; CHECK-LABEL: define void @foo2(%fum.1.2** %b, %fum.1** %a) {
+; CHECK-NEXT:   %a.copy = call %fum.1** @llvm.ssa.copy.p0p0s_fum.1s(%fum.1** %a)
+; CHECK-NEXT:  %b.copy = call %fum.1.2** @llvm.ssa.copy.p0p0s_fum.1.2s(%fum.1.2** %b)
+; CHECK-NEXT:  ret void
+
+