Merge pull request swiftlang#23088 from DougGregor/solver-disjunction-favoring

[Constraint solver] Generalize disjunction favoring

Author: DougGregor

lib/Sema/CSGen.cpp

@@ -595,107 +595,74 @@ namespace {
   /// of the overload set and call arguments.
   ///
   /// \param expr The application.
-  /// \param isFavored Determine whether the given overload is favored.
+  /// \param isFavored Determine whether the given overload is favored, passing
+  /// it the "effective" overload type when it's being called.
   /// \param mustConsider If provided, a function to detect the presence of
   /// overloads which inhibit any overload from being favored.
   void favorCallOverloads(ApplyExpr *expr,
                           ConstraintSystem &CS,
-                          llvm::function_ref<bool(ValueDecl *)> isFavored,
+                          llvm::function_ref<bool(ValueDecl *, Type)> isFavored,
                           std::function<bool(ValueDecl *)>
                               mustConsider = nullptr) {
     // Find the type variable associated with the function, if any.
     auto tyvarType = CS.getType(expr->getFn())->getAs<TypeVariableType>();
-    if (!tyvarType)
+    if (!tyvarType || CS.getFixedType(tyvarType))
       return;
 
     // This type variable is only currently associated with the function
     // being applied, and the only constraint attached to it should
     // be the disjunction constraint for the overload group.
-    auto &CG = CS.getConstraintGraph();
-    llvm::SetVector<Constraint *> disjunctions;
-    CG.gatherConstraints(tyvarType, disjunctions,
-                         ConstraintGraph::GatheringKind::EquivalenceClass,
-                         [](Constraint *constraint) -> bool {
-                           return constraint->getKind() ==
-                                  ConstraintKind::Disjunction;
-                         });
-    if (disjunctions.empty())
+    auto disjunction = CS.getUnboundBindOverloadDisjunction(tyvarType);
+    if (!disjunction)
       return;
 
-    // Look for the disjunction that binds the overload set.
-    for (auto *disjunction : disjunctions) {
-      auto oldConstraints = disjunction->getNestedConstraints();
-      auto csLoc = CS.getConstraintLocator(expr->getFn());
-      
-      // Only replace the disjunctive overload constraint.
-      if (oldConstraints[0]->getKind() != ConstraintKind::BindOverload) {
+    // Find the favored constraints and mark them.
+    SmallVector<Constraint *, 4> newlyFavoredConstraints;
+    unsigned numFavoredConstraints = 0;
+    Constraint *firstFavored = nullptr;
+    for (auto constraint : disjunction->getNestedConstraints()) {
+      if (!constraint->getOverloadChoice().isDecl())
         continue;
-      }
+      auto decl = constraint->getOverloadChoice().getDecl();
 
-      if (mustConsider) {
-        bool hasMustConsider = false;
-        for (auto oldConstraint : oldConstraints) {
-          auto overloadChoice = oldConstraint->getOverloadChoice();
-          if (overloadChoice.isDecl() &&
-              mustConsider(overloadChoice.getDecl()))
-            hasMustConsider = true;
-        }
-        if (hasMustConsider) {
-          continue;
-        }
-      }
+      if (mustConsider && mustConsider(decl)) {
+        // Roll back any constraints we favored.
+        for (auto favored : newlyFavoredConstraints)
+          favored->setFavored(false);
 
-      // Copy over the existing bindings, dividing the constraints up
-      // into "favored" and non-favored lists.
-      SmallVector<Constraint *, 4> favoredConstraints;
-      SmallVector<Constraint *, 4> fallbackConstraints;
-      for (auto oldConstraint : oldConstraints) {
-        if (!oldConstraint->getOverloadChoice().isDecl())
-          continue;
-        auto decl = oldConstraint->getOverloadChoice().getDecl();
-        if (!decl->getAttrs().isUnavailable(CS.getASTContext()) &&
-            isFavored(decl))
-          favoredConstraints.push_back(oldConstraint);
-        else
-          fallbackConstraints.push_back(oldConstraint);
+        return;
       }
 
-      // If we did not find any favored constraints, we're done.
-      if (favoredConstraints.empty()) break;
+      Type overloadType =
+          CS.getEffectiveOverloadType(constraint->getOverloadChoice(),
+                                      /*allowMembers=*/true, CS.DC);
+      if (!overloadType)
+        continue;
 
-      if (favoredConstraints.size() == 1) {
-        auto overloadChoice = favoredConstraints[0]->getOverloadChoice();
-        auto overloadType = overloadChoice.getDecl()->getInterfaceType();
-        auto resultType = overloadType->getAs<AnyFunctionType>()->getResult();
+      if (!decl->getAttrs().isUnavailable(CS.getASTContext()) &&
+          isFavored(decl, overloadType)) {
+        // If we might need to roll back the favored constraints, keep
+        // track of those we are favoring.
+        if (mustConsider && !constraint->isFavored())
+          newlyFavoredConstraints.push_back(constraint);
+
+        constraint->setFavored();
+        ++numFavoredConstraints;
+        if (!firstFavored)
+          firstFavored = constraint;
+      }
+    }
+
+    // If there was one favored constraint, set the favored type based on its
+    // result type.
+    if (numFavoredConstraints == 1) {
+      auto overloadChoice = firstFavored->getOverloadChoice();
+      auto overloadType =
+        CS.getEffectiveOverloadType(overloadChoice, /*allowMembers=*/true,
+                                    CS.DC);
+      auto resultType = overloadType->castTo<AnyFunctionType>()->getResult();
+      if (!resultType->hasTypeParameter())
         CS.setFavoredType(expr, resultType.getPointer());
-      }
-
-      // Remove the original constraint from the inactive constraint
-      // list and add the new one.
-      CS.removeInactiveConstraint(disjunction);
-
-      // Create the disjunction of favored constraints.
-      auto favoredConstraintsDisjunction =
-          Constraint::createDisjunction(CS,
-                                        favoredConstraints,
-                                        csLoc);
-      
-      favoredConstraintsDisjunction->setFavored();
-      
-      llvm::SmallVector<Constraint *, 2> aggregateConstraints;
-      aggregateConstraints.push_back(favoredConstraintsDisjunction);
-
-      if (!fallbackConstraints.empty()) {
-        // Find the disjunction of fallback constraints. If any
-        // constraints were added here, create a new disjunction.
-        Constraint *fallbackConstraintsDisjunction =
-          Constraint::createDisjunction(CS, fallbackConstraints, csLoc);
-
-        aggregateConstraints.push_back(fallbackConstraintsDisjunction);
-      }
-
-      CS.addDisjunctionConstraint(aggregateConstraints, csLoc);
-      break;
     }
   }
 
@@ -738,18 +705,11 @@ namespace {
   void favorMatchingUnaryOperators(ApplyExpr *expr,
                                    ConstraintSystem &CS) {
     // Determine whether the given declaration is favored.
-    auto isFavoredDecl = [&](ValueDecl *value) -> bool {
-      auto valueTy = value->getInterfaceType();
-      
-      auto fnTy = valueTy->getAs<AnyFunctionType>();
+    auto isFavoredDecl = [&](ValueDecl *value, Type type) -> bool {
+      auto fnTy = type->getAs<AnyFunctionType>();
       if (!fnTy)
         return false;
 
-      // Figure out the parameter type.
-      if (value->getDeclContext()->isTypeContext()) {
-        fnTy = fnTy->getResult()->castTo<AnyFunctionType>();
-      }
-
       Type paramTy = FunctionType::composeInput(CS.getASTContext(),
                                                 fnTy->getParams(), false);
       auto resultTy = fnTy->getResult();
@@ -791,10 +751,8 @@ namespace {
       }
 
       // Determine whether the given declaration is favored.
-      auto isFavoredDecl = [&](ValueDecl *value) -> bool {
-        auto valueTy = value->getInterfaceType();
-        
-        if (!valueTy->is<AnyFunctionType>())
+      auto isFavoredDecl = [&](ValueDecl *value, Type type) -> bool {
+        if (!type->is<AnyFunctionType>())
           return false;
 
         auto paramCount = getParamCount(value);
@@ -809,23 +767,11 @@ namespace {
 
     if (auto favoredTy = CS.getFavoredType(expr->getArg())) {
       // Determine whether the given declaration is favored.
-      auto isFavoredDecl = [&](ValueDecl *value) -> bool {
-        auto valueTy = value->getInterfaceType();
-        
-        auto fnTy = valueTy->getAs<AnyFunctionType>();
+      auto isFavoredDecl = [&](ValueDecl *value, Type type) -> bool {
+        auto fnTy = type->getAs<AnyFunctionType>();
         if (!fnTy)
           return false;
 
-        // Figure out the parameter type, accounting for the implicit 'self' if
-        // necessary.
-        if (auto *FD = dyn_cast<AbstractFunctionDecl>(value)) {
-          if (FD->hasImplicitSelfDecl()) {
-            if (auto resFnTy = fnTy->getResult()->getAs<AnyFunctionType>()) {
-              fnTy = resFnTy;
-            }
-          }
-        }
-
         auto paramTy =
             AnyFunctionType::composeInput(CS.getASTContext(), fnTy->getParams(),
                                           /*canonicalVararg*/ false);
@@ -884,10 +830,8 @@ namespace {
     };
 
     // Determine whether the given declaration is favored.
-    auto isFavoredDecl = [&](ValueDecl *value) -> bool {
-      auto valueTy = value->getInterfaceType();
-      
-      auto fnTy = valueTy->getAs<AnyFunctionType>();
+    auto isFavoredDecl = [&](ValueDecl *value, Type type) -> bool {
+      auto fnTy = type->getAs<AnyFunctionType>();
       if (!fnTy)
         return false;
 
@@ -913,11 +857,6 @@ namespace {
         }
       }
 
-      // Figure out the parameter type.
-      if (value->getDeclContext()->isTypeContext()) {
-        fnTy = fnTy->getResult()->castTo<AnyFunctionType>();
-      }
-
       auto params = fnTy->getParams();
       if (params.size() != 2)
         return false;

lib/Sema/CSSimplify.cpp

@@ -4538,7 +4538,6 @@ ConstraintSystem::simplifyEscapableFunctionOfConstraint(
     return SolutionKind::Unsolved;
   };
 
-
   type2 = getFixedTypeRecursive(type2, flags, /*wantRValue=*/true);
   if (auto fn2 = type2->getAs<FunctionType>()) {
     // Solve forward by binding the other type variable to the escapable
@@ -5037,6 +5036,33 @@ Type ConstraintSystem::simplifyAppliedOverloads(
     break;
   }
 
+  // Collect the active overload choices.
+  SmallVector<OverloadChoice, 4> choices;
+  for (auto constraint : disjunction->getNestedConstraints()) {
+    if (constraint->isDisabled())
+      continue;
+    choices.push_back(constraint->getOverloadChoice());
+  }
+
+  // If we can favor one generic result over another, do so.
+  if (auto favoredChoice = tryOptimizeGenericDisjunction(choices)) {
+    unsigned favoredIndex = favoredChoice - choices.data();
+    for (auto constraint : disjunction->getNestedConstraints()) {
+      if (constraint->isDisabled())
+        continue;
+
+      if (favoredIndex == 0) {
+        if (solverState)
+          solverState->favorConstraint(constraint);
+        else
+          constraint->setFavored();
+
+        break;
+      } else {
+        --favoredIndex;
+      }
+    }
+  }
 
   // If there was a constraint that we couldn't reason about, don't use the
   // results of any common-type computations.

lib/Sema/CSSolver.cpp

@@ -424,6 +424,7 @@ ConstraintSystem::SolverScope::SolverScope(ConstraintSystem &cs)
   numCheckedConformances = cs.CheckedConformances.size();
   numMissingMembers = cs.MissingMembers.size();
   numDisabledConstraints = cs.solverState->getNumDisabledConstraints();
+  numFavoredConstraints = cs.solverState->getNumFavoredConstraints();
 
   PreviousScore = cs.CurrentScore;
 
@@ -1909,21 +1910,6 @@ void ConstraintSystem::partitionForDesignatedTypes(
 void ConstraintSystem::partitionDisjunction(
     ArrayRef<Constraint *> Choices, SmallVectorImpl<unsigned> &Ordering,
     SmallVectorImpl<unsigned> &PartitionBeginning) {
-  // Maintain the original ordering, and make a single partition of
-  // disjunction choices.
-  auto originalOrdering = [&]() {
-    for (unsigned long i = 0, e = Choices.size(); i != e; ++i)
-      Ordering.push_back(i);
-
-    PartitionBeginning.push_back(0);
-  };
-
-  if (!TC.getLangOpts().SolverEnableOperatorDesignatedTypes ||
-      !isOperatorBindOverload(Choices[0])) {
-    originalOrdering();
-    return;
-  }
-
   SmallSet<Constraint *, 16> taken;
 
   // Local function used to iterate over the untaken choices from the
@@ -1937,33 +1923,45 @@ void ConstraintSystem::partitionDisjunction(
           if (taken.count(constraint))
             continue;
 
-          assert(constraint->getKind() == ConstraintKind::BindOverload);
-          assert(constraint->getOverloadChoice().isDecl());
-
           if (fn(index, constraint))
             taken.insert(constraint);
         }
       };
 
-  // First collect some things that we'll generally put near the end
-  // of the partitioning.
+  // First collect some things that we'll generally put near the beginning or
+  // end of the partitioning.
 
+  SmallVector<unsigned, 4> favored;
   SmallVector<unsigned, 4> disabled;
   SmallVector<unsigned, 4> unavailable;
 
-  // First collect disabled constraints.
+  // First collect disabled and favored constraints.
   forEachChoice(Choices, [&](unsigned index, Constraint *constraint) -> bool {
-    if (!constraint->isDisabled())
-      return false;
-    disabled.push_back(index);
-    return true;
+    if (constraint->isDisabled()) {
+      disabled.push_back(index);
+      return true;
+    }
+
+    if (constraint->isFavored()) {
+      favored.push_back(index);
+      return true;
+    }
+
+    return false;
   });
 
   // Then unavailable constraints if we're skipping them.
   if (!shouldAttemptFixes()) {
     forEachChoice(Choices, [&](unsigned index, Constraint *constraint) -> bool {
+      if (constraint->getKind() != ConstraintKind::BindOverload)
+        return false;
+      if (!constraint->getOverloadChoice().isDecl())
+        return false;
+
       auto *decl = constraint->getOverloadChoice().getDecl();
-      auto *funcDecl = cast<FuncDecl>(decl);
+      auto *funcDecl = dyn_cast<FuncDecl>(decl);
+      if (!funcDecl)
+        return false;
 
       if (!funcDecl->getAttrs().isUnavailable(getASTContext()))
         return false;
@@ -1983,14 +1981,18 @@ void ConstraintSystem::partitionDisjunction(
         }
       };
 
-  partitionForDesignatedTypes(Choices, forEachChoice, appendPartition);
+  if (TC.getLangOpts().SolverEnableOperatorDesignatedTypes &&
+      isOperatorBindOverload(Choices[0])) {
+    partitionForDesignatedTypes(Choices, forEachChoice, appendPartition);
+  }
 
   SmallVector<unsigned, 4> everythingElse;
   // Gather the remaining options.
   forEachChoice(Choices, [&](unsigned index, Constraint *constraint) -> bool {
     everythingElse.push_back(index);
     return true;
   });
+  appendPartition(favored);
   appendPartition(everythingElse);
 
   // Now create the remaining partitions from what we previously collected.

lib/Sema/Constraint.h

@@ -444,7 +444,7 @@ class Constraint final : public llvm::ilist_node<Constraint>,
   }
 
   /// Mark or retrieve whether this constraint should be favored in the system.
-  void setFavored() { IsFavored = true; }
+  void setFavored(bool favored = true) { IsFavored = favored; }
   bool isFavored() const { return IsFavored; }
 
   /// Whether the solver should remember which choice was taken for