Index: lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp
===================================================================
--- lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp
+++ lib/Target/WebAssembly/WebAssemblyAddMissingPrototypes.cpp
@@ -96,9 +96,10 @@
           if (!NewType) {
             // Create a new function with the correct type
             NewType = DestType;
-            NewF = Function::Create(NewType, F.getLinkage(), F.getName());
+            NewF = Function::Create(NewType, F.getLinkage(), F.getName() + ".fixed_sig");
             NewF->setAttributes(F.getAttributes());
             NewF->removeFnAttr("no-prototype");
+            Replacements.emplace_back(&F, NewF);
           } else {
             if (NewType != DestType) {
               report_fatal_error("Prototypeless function used with "
@@ -116,45 +117,17 @@
                         F.getName() + "\n");
       continue;
     }
-
-    SmallVector<Instruction *, 4> DeadInsts;
-
-    for (Use &US : F.uses()) {
-      User *U = US.getUser();
-      if (auto *BC = dyn_cast<BitCastOperator>(U)) {
-        if (auto *Inst = dyn_cast<BitCastInst>(U)) {
-          // Replace with a new bitcast
-          IRBuilder<> Builder(Inst);
-          Value *NewCast = Builder.CreatePointerCast(NewF, BC->getDestTy());
-          Inst->replaceAllUsesWith(NewCast);
-          DeadInsts.push_back(Inst);
-        } else if (auto *Const = dyn_cast<ConstantExpr>(U)) {
-          Constant *NewConst =
-              ConstantExpr::getPointerCast(NewF, BC->getDestTy());
-          Const->replaceAllUsesWith(NewConst);
-        } else {
-          dbgs() << *U->getType() << "\n";
-#ifndef NDEBUG
-          U->dump();
-#endif
-          report_fatal_error("unexpected use of prototypeless function: " +
-                             F.getName() + "\n");
-        }
-      }
-    }
-
-    for (auto I : DeadInsts)
-      I->eraseFromParent();
-    Replacements.emplace_back(&F, NewF);
   }
 
-
-  // Finally replace the old function declarations with the new ones
   for (auto &Pair : Replacements) {
-    Function *Old = Pair.first;
-    Function *New = Pair.second;
-    Old->eraseFromParent();
-    M.getFunctionList().push_back(New);
+    Function *OldF = Pair.first;
+    Function *NewF = Pair.second;
+    std::string Name = OldF->getName();
+    M.getFunctionList().push_back(NewF);
+    OldF->replaceAllUsesWith(
+      ConstantExpr::getPointerBitCastOrAddrSpaceCast(NewF, OldF->getType()));
+    OldF->eraseFromParent();
+    NewF->setName(Name);
   }
 
   return !Replacements.empty();
Index: test/CodeGen/WebAssembly/add-prototypes.ll
===================================================================
--- test/CodeGen/WebAssembly/add-prototypes.ll
+++ test/CodeGen/WebAssembly/add-prototypes.ll
@@ -17,7 +17,8 @@
 }
 
 ; CHECK-LABEL: @call_foo_ptr
-; CHECK: %call = call i64 @foo(i32 43)
+; CHECK: %1 = bitcast i64 (...)* bitcast (i64 (i32)* @foo to i64 (...)*) to i64 (i32)*
+; CHECK-NEXT: %call = call i64 %1(i32 43)
 define i64 @call_foo_ptr(i32 %a) {
   %1 = bitcast i64 (...)* @foo to i64 (i32)*
   %call = call i64 (i32) %1(i32 43)
@@ -25,7 +26,8 @@
 }
 
 ; CHECK-LABEL: @to_intptr_inst
-; CHECK: ret i8* bitcast (i64 (i32)* @foo to i8*)
+; CHECK: %1 = bitcast i64 (...)* bitcast (i64 (i32)* @foo to i64 (...)*) to i8*
+; CHECK-NEXT: ret i8* %1
 define i8* @to_intptr_inst() {
   %1 = bitcast i64 (...)* @foo to i8*
   ret i8* %1
@@ -37,8 +39,27 @@
   ret i8* bitcast (i64 (...)* @foo to i8*)
 }
 
-; CHECK: declare i64 @foo(i32)
-declare i64 @foo(...) #1
+; CHECK-LABEL: @null_compare
+; CHECK: br i1 icmp eq (i64 (...)* bitcast (i64 (i32)* @foo to i64 (...)*), i64 (...)* null), label %if.then, label %if.end
+define i8 @null_compare() {
+  br i1 icmp eq (i64 (...)* @foo, i64 (...)* null), label %if.then, label %if.end
+if.then:
+  ret i8 0
+if.end:
+  ret i8 1
+}
+
+; CHECK-LABEL: @as_paramater
+; CHECK: call void @func_param(i64 (...)* bitcast (i64 (i32)* @foo to i64 (...)*))
+define void @as_paramater() {
+  call void @func_param(i64 (...)* @foo)
+  ret void
+}
+
+declare void @func_param(i64 (...)*)
+
+; CHECK: declare extern_weak i64 @foo(i32)
+declare extern_weak i64 @foo(...) #1
 
 ; CHECK-NOT: attributes {{.*}} = { {{.*}}"no-prototype"{{.*}} }
 attributes #1 = { "no-prototype" }