[CSOptimizer] Allow generic operator overloads without associated type parameters

lib/Sema/CSOptimizer.cpp

@@ -14,6 +14,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "TypeChecker.h"
+#include "swift/AST/GenericSignature.h"
 #include "swift/Sema/ConstraintGraph.h"
 #include "swift/Sema/ConstraintSystem.h"
 #include "llvm/ADT/BitVector.h"
@@ -86,34 +88,6 @@ 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
@@ -181,23 +155,6 @@ 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;
@@ -205,8 +162,21 @@ static void determineBestChoicesInContext(
     forEachDisjunctionChoice(
         cs, disjunction,
         [&](Constraint *choice, ValueDecl *decl, FunctionType *overloadType) {
-          if (!isViableOverload(decl))
-            return;
+          GenericSignature genericSig;
+          {
+            if (auto *GF = dyn_cast<AbstractFunctionDecl>(decl)) {
+              genericSig = GF->getGenericSignature();
+            } else if (auto *SD = dyn_cast<SubscriptDecl>(decl)) {
+              genericSig = SD->getGenericSignature();
+            }
+
+            // Let's not consider non-operator generic overloads because we
+            // need conformance checking functionality to determine best
+            // favoring, preferring such overloads based on concrete types
+            // alone leads to subpar choices due to missed information.
+            if (genericSig && !decl->isOperator())
+              return;
+          }
 
           ParameterListInfo paramListInfo(
               overloadType->getParams(), decl,
@@ -249,6 +219,23 @@ static void determineBestChoicesInContext(
             if (candidateArgumentTypes[i].empty())
               continue;
 
+            // Check protocol requirement(s) if this parameter is a
+            // generic parameter type.
+            GenericSignature::RequiredProtocols protocolRequirements;
+            if (genericSig) {
+              if (auto *GP = paramType->getAs<GenericTypeParamType>()) {
+                protocolRequirements = genericSig->getRequiredProtocols(GP);
+                // It's a generic parameter which might be connected via
+                // same-type constraints to other generic parameters but
+                // we cannot check that here, so let's ignore it.
+                if (protocolRequirements.empty())
+                  continue;
+              }
+
+              if (paramType->getAs<DependentMemberType>())
+                return;
+            }
+
             // The idea here is to match the parameter type against
             // all of the argument candidate types and pick the best
             // match (i.e. exact equality one).
@@ -281,22 +268,36 @@ static void determineBestChoicesInContext(
 
               // The specifier only matters for `inout` check.
               candidateType = candidateType->getWithoutSpecifierType();
-              // Exact match on one of the candidate bindings.
-              if (candidateType->isEqual(paramType)) {
+
+              // We don't check generic requirements against literal default
+              // types because it creates more noise than signal for operators.
+              if (!protocolRequirements.empty() && !isLiteralDefault) {
+                if (llvm::all_of(
+                        protocolRequirements, [&](ProtocolDecl *protocol) {
+                          return TypeChecker::conformsToProtocol(
+                              candidateType, protocol, cs.DC->getParentModule(),
+                              /*allowMissing=*/false);
+                        })) {
+                  // Score is lower here because we still prefer concrete
+                  // overloads over the generic ones when possible.
+                  bestCandidateScore = std::max(bestCandidateScore, 0.7);
+                  continue;
+                }
+              } else if (paramType->hasTypeParameter()) {
+                // i.e. Array<Element> or Optional<Wrapped> as a parameter.
+                // This is slightly better than all of the conformances matching
+                // because the parameter is concrete and could split the graph.
+                if (paramType->getAnyNominal() == candidateType->getAnyNominal()) {
+                  bestCandidateScore = std::max(bestCandidateScore, 0.8);
+                  continue;
+                }
+              } else if (candidateType->isEqual(paramType)) {
+                // Exact match on one of the candidate bindings.
                 bestCandidateScore =
                     std::max(bestCandidateScore, isLiteralDefault ? 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)) {
-                bestCandidateScore = 1.0;
-                continue;
-              }
-
               // Only established arguments could be considered mismatches,
               // literal default types should be regarded as holes if they
               // didn't match.

validation-test/Sema/type_checker_perf/fast/rdar17170728.swift

@@ -5,7 +5,6 @@ let i: Int? = 1
 let j: Int?
 let k: Int? = 2
 
-// expected-error@+1 {{the compiler is unable to type-check this expression in reasonable time}}
 let _ = [i, j, k].reduce(0 as Int?) {
   $0 != nil && $1 != nil ? $0! + $1! : ($0 != nil ? $0! : ($1 != nil ? $1! : nil))
 }