Don't perform ADL when looking up operator=; there is no non-member form of

that function, and apart from being slow, this is unnecessary: ADL can trigger
instantiations that are not permitted here. The standard isn't *completely*
clear here, but this seems like the intent, and in any case this approach is
permitted by [temp.inst]p7.

llvm-svn: 218330

clang/lib/Sema/SemaOverload.cpp

@@ -11031,10 +11031,13 @@ Sema::CreateOverloadedBinOp(SourceLocation OpLoc,
   // Add operator candidates that are member functions.
   AddMemberOperatorCandidates(Op, OpLoc, Args, CandidateSet);
 
-  // Add candidates from ADL.
-  AddArgumentDependentLookupCandidates(OpName, OpLoc, Args,
-                                       /*ExplicitTemplateArgs*/ nullptr,
-                                       CandidateSet);
+  // Add candidates from ADL. Per [over.match.oper]p2, this lookup is not
+  // performed for an assignment operator (nor for operator[] nor operator->,
+  // which don't get here).
+  if (Opc != BO_Assign)
+    AddArgumentDependentLookupCandidates(OpName, OpLoc, Args,
+                                         /*ExplicitTemplateArgs*/ nullptr,
+                                         CandidateSet);
 
   // Add builtin operator candidates.
   AddBuiltinOperatorCandidates(Op, OpLoc, Args, CandidateSet);