[CSOptimizer] Prefer homogeneous arithmetic operator overloads when argument(s) or result match

This is an opportunistic optimization based on the operator
use patterns where homogeneous operators are the most
heavily used ones.

Author: xedin

lib/Sema/CSOptimizer.cpp

@@ -493,6 +493,24 @@ static void determineBestChoicesInContext(
           }
 
           if (score > 0) {
+            if (decl->isOperator() &&
+                decl->getBaseIdentifier().isArithmeticOperator() &&
+                overloadType->getNumParams() == 2) {
+              // Nudge the score slightly to prefer concrete homogeneous
+              // operators.
+              //
+              // This is an opportunistic optimization based on the operator
+              // use patterns where homogeneous operators are the most
+              // heavily used ones.
+              auto resultTy = overloadType->getResult();
+              if (!resultTy->hasTypeParameter() &&
+                  llvm::all_of(overloadType->getParams(),
+                               [&resultTy](const auto &param) {
+                                 return param.getPlainType()->isEqual(resultTy);
+                               }))
+                score += 0.001;
+            }
+
             favoredChoices.push_back({choice, score});
             bestScore = std::max(bestScore, score);
           }