Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -7840,6 +7840,8 @@
   "this builtin is only available on x86-64 targets">;
 def err_x86_builtin_invalid_rounding : Error<
   "invalid rounding argument">;
+def err_x86_sse_register : Error<
+  "SSE register return with SSE disabled">;
 
 def err_builtin_longjmp_unsupported : Error<
   "__builtin_longjmp is not supported for the current target">;
Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -2474,6 +2474,17 @@
         CheckArgumentWithTypeTag(I, Args.data());
     }
   }
+
+  // Don't allow calls returning floating point scalars when
+  // target == x86_64 && SSE disabled.
+  if (Context.getTargetInfo().getTriple().getArch() == llvm::Triple::x86_64 &&
+      (!Context.getTargetInfo().hasFeature("sse") ||
+       !Context.getTargetInfo().hasFeature("sse2"))) {
+    if (auto *ResultType = Proto->getReturnType().getTypePtrOrNull()) {
+      if (ResultType->isRealFloatingType())
+        Diag(Loc, diag::err_x86_sse_register);
+    }
+  }
 }
 
 /// CheckConstructorCall - Check a constructor call for correctness and safety