Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -318,6 +318,9 @@
 def TargetELF : TargetSpec {
   let ObjectFormats = ["ELF"];
 }
+def TargetSupportsAlias : TargetSpec {
+  let ObjectFormats = ["COFF", "ELF", "Wasm"];
+}
 
 // Attribute subject match rules that are used for #pragma clang attribute.
 //
@@ -554,7 +557,7 @@
   let Documentation = [Undocumented];
 }
 
-def Alias : Attr {
+def Alias : Attr, TargetSpecificAttr<TargetSupportsAlias> {
   let Spellings = [GCC<"alias">];
   let Args = [StringArgument<"Aliasee">];
   let Subjects = SubjectList<[Function, GlobalVar], ErrorDiag>;
Index: test/Sema/attr-alias-has.c
===================================================================
--- /dev/null
+++ test/Sema/attr-alias-has.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin  -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple i686-pc-linux-gnu  -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple i686-unknown-windows-msvc  -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple wasm32-unknown-unknown -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple wasm64-unknown-unknown -fsyntax-only -verify %s
+
+void g() {}
+#if !__has_attribute(alias) 
+void f() __attribute__((alias("g"))); // expected-warning {{unknown attribute 'alias' ignored}}
+#else
+void f() __attribute__((alias("g"))); // expected-no-diagnostics
+#endif
\ No newline at end of file
Index: test/Sema/attr-alias.c
===================================================================
--- test/Sema/attr-alias.c
+++ test/Sema/attr-alias.c
@@ -2,4 +2,4 @@
 
 void g() {}
 
-void f() __attribute__((alias("g"))); //expected-error {{aliases are not supported on darwin}}
+void f() __attribute__((alias("g"))); //expected-warning {{unknown attribute 'alias' ignored}}