Compute potential bindings with the help of the constraint graph.

Rather than performing a two-pass walk over all of the constraints in
the system to attach them to type variables, use the existing type
variable -> constraints mapping in the constraint graph to make this a
faster single-pass process. Also clarify the type bindings a little
bit. Improves type checking time for the standard library by ~3%.



Swift SVN r11098

lib/Sema/CSSimplify.cpp

@@ -1426,6 +1426,13 @@ ConstraintSystem::simplifyMemberConstraint(const Constraint &constraint) {
       choices.push_back(OverloadChoice(baseTy, result.first,
                                        /*isSpecialized=*/false));
     }
+
+    if (choices.empty()) {
+      recordFailure(constraint.getLocator(), Failure::DoesNotHaveMember,
+                    baseObjTy, name);
+      return SolutionKind::Error;
+    }
+
     auto locator = getConstraintLocator(constraint.getLocator());
     addOverloadSet(memberTy, choices, locator);
     return SolutionKind::Solved;