[CSOptimizer] Favor SIMD related arithmetic operator choices if argument is SIMD<N> type

lib/Sema/CSOptimizer.cpp

@@ -85,6 +85,34 @@ void forEachDisjunctionChoice(
   }
 }
 
+static bool isSIMDType(Type type) {
+  auto *NTD = dyn_cast_or_null<StructDecl>(type->getAnyNominal());
+  if (!NTD)
+    return false;
+
+  auto typeName = NTD->getName().str();
+  if (!typeName.startswith("SIMD"))
+    return false;
+
+  return NTD->getParentModule()->getName().is("Swift");
+}
+
+static bool isArithmeticOperatorOnSIMDProtocol(ValueDecl *decl) {
+  if (!isSIMDOperator(decl))
+    return false;
+
+  if (!decl->getBaseIdentifier().isArithmeticOperator())
+    return false;
+
+  auto *DC = decl->getDeclContext();
+  if (auto *P = DC->getSelfProtocolDecl()) {
+    if (auto knownKind = P->getKnownProtocolKind())
+      return *knownKind == KnownProtocolKind::SIMD;
+  }
+
+  return false;
+}
+
 } // end anonymous namespace
 
 /// Given a set of disjunctions, attempt to determine
@@ -152,6 +180,23 @@ static void determineBestChoicesInContext(
       resultTypes.push_back(resultType);
     }
 
+    auto isViableOverload = [&](ValueDecl *decl) {
+      // Allow standard arithmetic operator overloads on SIMD protocol
+      // to be considered because we can favor them when then argument
+      // is a known SIMD<N> type.
+      if (isArithmeticOperatorOnSIMDProtocol(decl))
+        return true;
+
+      // Don't consider generic overloads because we need conformance
+      // checking functionality to determine best favoring, preferring
+      // such overloads based only on concrete types leads to subpar
+      // choices due to missed information.
+      if (decl->getInterfaceType()->is<GenericFunctionType>())
+        return false;
+
+      return true;
+    };
+
     // The choice with the best score.
     double bestScore = 0.0;
     SmallVector<std::pair<Constraint *, double>, 2> favoredChoices;
@@ -159,11 +204,7 @@ static void determineBestChoicesInContext(
     forEachDisjunctionChoice(
         cs, disjunction,
         [&](Constraint *choice, ValueDecl *decl, FunctionType *overloadType) {
-          // Don't consider generic overloads because we need conformance
-          // checking functionality to determine best favoring, preferring
-          // such overloads based only on concrete types leads to subpar
-          // choices due to missed information.
-          if (decl->getInterfaceType()->is<GenericFunctionType>())
+          if (!isViableOverload(decl))
             return;
 
           if (overloadType->getNumParams() != argFuncType->getNumParams())
@@ -204,6 +245,16 @@ static void determineBestChoicesInContext(
               if (candidateType->isEqual(paramType)) {
                 argScore = std::max(
                     argScore, /*fromLiteral=*/candidate.second ? 0.3 : 1.0);
+                continue;
+              }
+
+              // If argument is SIMD<N> type i.e. SIMD1<...> it's appropriate
+              // to favor of the overloads that are declared on SIMD protocol
+              // and expect a particular `Scalar` if it's known.
+              if (isSIMDType(candidateType) &&
+                  isArithmeticOperatorOnSIMDProtocol(decl)) {
+                argScore = std::max(argScore, 1.0);
+                continue;
               }
             }