[ConstraintSystem] Better handling of operators with multiple designated types.

For operators with multiple designated types, we attempt to decide the
best order for exploring the types. We were doing this by checking
for matching types. Extend this to also consider conforming types.

Fixes: rdar://problem/46687985

Author: rudkx

lib/Sema/CSSolver.cpp

@@ -1670,11 +1670,18 @@ void ConstraintSystem::sortDesignatedTypes(
   size_t nextType = 0;
   for (auto argType : argInfo.getTypes()) {
     auto *nominal = argType->getAnyNominal();
-    for (size_t i = nextType + 1; i < nominalTypes.size(); ++i) {
+    for (size_t i = nextType; i < nominalTypes.size(); ++i) {
       if (nominal == nominalTypes[i]) {
         std::swap(nominalTypes[nextType], nominalTypes[i]);
         ++nextType;
         break;
+      } else if (auto *protoDecl = dyn_cast<ProtocolDecl>(nominalTypes[i])) {
+        if (TC.conformsToProtocol(argType, protoDecl, DC,
+                                  ConformanceCheckFlags::InExpression)) {
+          std::swap(nominalTypes[nextType], nominalTypes[i]);
+          ++nextType;
+          break;
+        }
       }
     }
   }

validation-test/Sema/type_checker_perf/fast/rdar46687985.swift

@@ -0,0 +1,5 @@
+// RUN: %target-typecheck-verify-swift -solver-expression-time-threshold=1 -solver-enable-operator-designated-types
+
+func test(_ d: Double) -> Double {
+  return d + d - d - (d / 2) + (d / 2) + (d / 2.0)
+}