[Constraint] Allow constraints to be disabled only in "performance" mode

Author: xedin

include/swift/Sema/Constraint.h

@@ -324,6 +324,10 @@ class Constraint final : public llvm::ilist_node<Constraint>,
   /// constraint graph during constraint propagation?
   unsigned IsDisabled : 1;
 
+  /// Constraint is disabled in performance mode only, could be attempted
+  /// for diagnostic purposes.
+  unsigned IsDisabledForPerformance : 1;
+
   /// Whether the choice of this disjunction should be recorded in the
   /// solver state.
   unsigned RememberChoice : 1;
@@ -542,18 +546,27 @@ class Constraint final : public llvm::ilist_node<Constraint>,
     IsActive = active;
   }
 
-  /// Whether this constraint is active, i.e., in the worklist.
-  bool isDisabled() const { return IsDisabled; }
+  /// Whether this constraint is disabled and shouldn't be attempted by the
+  /// solver.
+  bool isDisabled() const { return IsDisabled || IsDisabledForPerformance; }
+
+  /// Whether this constraint is disabled and shouldn't be attempted by the
+  /// solver only in "performance" mode.
+  bool isDisabledInPerformanceMode() const { return IsDisabledForPerformance; }
 
   /// Set whether this constraint is active or not.
-  void setDisabled() {
+  void setDisabled(bool enableForDiagnostics = false) {
     assert(!isActive() && "Cannot disable constraint marked as active!");
-    IsDisabled = true;
+    if (enableForDiagnostics)
+      IsDisabledForPerformance = true;
+    else
+      IsDisabled = true;
   }
 
   void setEnabled() {
     assert(isDisabled() && "Can't re-enable already active constraint!");
     IsDisabled = false;
+    IsDisabledForPerformance = false;
   }
 
   /// Mark or retrieve whether this constraint should be favored in the system.

include/swift/Sema/ConstraintSystem.h

@@ -5301,7 +5301,20 @@ class DisjunctionChoice {
 
   bool attempt(ConstraintSystem &cs) const;
 
-  bool isDisabled() const { return Choice->isDisabled(); }
+  bool isDisabled() const {
+    if (!Choice->isDisabled())
+      return false;
+
+    // If solver is in a diagnostic mode, let's allow
+    // constraints that have fixes or have been disabled
+    // in attempt to produce a solution faster for
+    // well-formed expressions.
+    if (CS.shouldAttemptFixes()) {
+      return !(hasFix() || Choice->isDisabledInPerformanceMode());
+    }
+
+    return true;
+  }
 
   bool hasFix() const {
     return bool(Choice->getFix());

lib/Sema/CSStep.cpp

@@ -612,7 +612,7 @@ bool DisjunctionStep::shouldSkip(const DisjunctionChoice &choice) const {
 
   // Skip disabled overloads in the diagnostic mode if they do not have a
   // fix attached to them e.g. overloads where labels didn't match up.
-  if (choice.isDisabled() && !(CS.shouldAttemptFixes() && choice.hasFix()))
+  if (choice.isDisabled())
     return skip("disabled");
 
   // Skip unavailable overloads (unless in dignostic mode).

lib/Sema/Constraint.cpp

@@ -30,7 +30,7 @@ Constraint::Constraint(ConstraintKind kind, ArrayRef<Constraint *> constraints,
                        ConstraintLocator *locator,
                        SmallPtrSetImpl<TypeVariableType *> &typeVars)
     : Kind(kind), HasRestriction(false), IsActive(false), IsDisabled(false),
-      RememberChoice(false), IsFavored(false),
+      IsDisabledForPerformance(false), RememberChoice(false), IsFavored(false),
       NumTypeVariables(typeVars.size()), Nested(constraints), Locator(locator) {
   assert(kind == ConstraintKind::Disjunction);
   std::uninitialized_copy(typeVars.begin(), typeVars.end(),
@@ -41,7 +41,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second,
                        ConstraintLocator *locator,
                        SmallPtrSetImpl<TypeVariableType *> &typeVars)
     : Kind(Kind), HasRestriction(false), IsActive(false), IsDisabled(false),
-      RememberChoice(false), IsFavored(false),
+      IsDisabledForPerformance(false), RememberChoice(false), IsFavored(false),
       NumTypeVariables(typeVars.size()), Types{First, Second, Type()},
       Locator(locator) {
   switch (Kind) {
@@ -110,7 +110,7 @@ Constraint::Constraint(ConstraintKind Kind, Type First, Type Second, Type Third,
                        ConstraintLocator *locator,
                        SmallPtrSetImpl<TypeVariableType *> &typeVars)
     : Kind(Kind), HasRestriction(false), IsActive(false), IsDisabled(false),
-      RememberChoice(false), IsFavored(false),
+      IsDisabledForPerformance(false), RememberChoice(false), IsFavored(false),
       NumTypeVariables(typeVars.size()), Types{First, Second, Third},
       Locator(locator) {
   switch (Kind) {
@@ -168,7 +168,7 @@ Constraint::Constraint(ConstraintKind kind, Type first, Type second,
                        ConstraintLocator *locator,
                        SmallPtrSetImpl<TypeVariableType *> &typeVars)
     : Kind(kind), HasRestriction(false), IsActive(false), IsDisabled(false),
-      RememberChoice(false), IsFavored(false),
+      IsDisabledForPerformance(false), RememberChoice(false), IsFavored(false),
       NumTypeVariables(typeVars.size()), Member{first, second, {member}, useDC},
       Locator(locator) {
   assert(kind == ConstraintKind::ValueMember ||
@@ -187,7 +187,7 @@ Constraint::Constraint(ConstraintKind kind, Type first, Type second,
                        ConstraintLocator *locator,
                        SmallPtrSetImpl<TypeVariableType *> &typeVars)
     : Kind(kind), HasRestriction(false), IsActive(false), IsDisabled(false),
-      RememberChoice(false), IsFavored(false),
+      IsDisabledForPerformance(false), RememberChoice(false), IsFavored(false),
       NumTypeVariables(typeVars.size()), Locator(locator) {
   Member.First = first;
   Member.Second = second;
@@ -207,8 +207,8 @@ Constraint::Constraint(Type type, OverloadChoice choice, DeclContext *useDC,
                        ConstraintFix *fix, ConstraintLocator *locator,
                        SmallPtrSetImpl<TypeVariableType *> &typeVars)
     : Kind(ConstraintKind::BindOverload), TheFix(fix), HasRestriction(false),
-      IsActive(false), IsDisabled(bool(fix)), RememberChoice(false),
-      IsFavored(false),
+      IsActive(false), IsDisabled(bool(fix)), IsDisabledForPerformance(false),
+      RememberChoice(false), IsFavored(false),
       NumTypeVariables(typeVars.size()), Overload{type, choice, useDC},
       Locator(locator) {
   std::copy(typeVars.begin(), typeVars.end(), getTypeVariablesBuffer().begin());
@@ -219,8 +219,8 @@ Constraint::Constraint(ConstraintKind kind,
                        Type second, ConstraintLocator *locator,
                        SmallPtrSetImpl<TypeVariableType *> &typeVars)
     : Kind(kind), Restriction(restriction), HasRestriction(true),
-      IsActive(false), IsDisabled(false), RememberChoice(false),
-      IsFavored(false),
+      IsActive(false), IsDisabled(false), IsDisabledForPerformance(false),
+      RememberChoice(false), IsFavored(false),
       NumTypeVariables(typeVars.size()), Types{first, second, Type()},
       Locator(locator) {
   assert(!first.isNull());
@@ -232,7 +232,8 @@ Constraint::Constraint(ConstraintKind kind, ConstraintFix *fix, Type first,
                        Type second, ConstraintLocator *locator,
                        SmallPtrSetImpl<TypeVariableType *> &typeVars)
     : Kind(kind), TheFix(fix), HasRestriction(false), IsActive(false),
-      IsDisabled(false), RememberChoice(false), IsFavored(false),
+      IsDisabled(false), IsDisabledForPerformance(false), RememberChoice(false),
+      IsFavored(false),
       NumTypeVariables(typeVars.size()), Types{first, second, Type()},
       Locator(locator) {
   assert(!first.isNull());