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Sema: Factor out SolverTrail from ConstraintGraph
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8 files changed

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-297
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8 files changed

+425
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Diff for: ‎include/swift/Sema/CSTrail.h

+138
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,138 @@
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//===--- CSTrail.h - Constraint Solver Trail --------------------*- C++ -*-===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the \c SolverTrail class, which records the decisions taken
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// while attempting to find a solution.
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//
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_SEMA_CSTRAIL_H
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#define SWIFT_SEMA_CSTRAIL_H
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#include <vector>
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namespace llvm {
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class raw_ostream;
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}
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namespace swift {
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class TypeBase;
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class TypeVariableType;
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namespace constraints {
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class Constraint;
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class ConstraintGraphScope;
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class SolverTrail {
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public:
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/// The kind of change made to the graph.
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enum class ChangeKind {
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/// Added a type variable to the constraint graph.
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AddedTypeVariable,
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/// Added a new constraint to the constraint graph.
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AddedConstraint,
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/// Removed an existing constraint from the constraint graph.
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RemovedConstraint,
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/// Extended the equivalence class of a type variable in the constraint graph.
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ExtendedEquivalenceClass,
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/// Added a fixed binding for a type variable in the constraint graph.
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BoundTypeVariable,
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};
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/// A change made to the constraint system.
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///
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/// Each change can be undone (once, and in reverse order) by calling the
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/// undo() method.
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class Change {
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public:
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/// The kind of change.
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ChangeKind Kind;
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union {
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TypeVariableType *TypeVar;
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Constraint *TheConstraint;
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struct {
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/// The type variable whose equivalence class was extended.
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TypeVariableType *TypeVar;
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/// The previous size of the equivalence class.
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unsigned PrevSize;
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} EquivClass;
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struct {
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/// The type variable being bound to a fixed type.
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TypeVariableType *TypeVar;
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/// The fixed type to which the type variable was bound.
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TypeBase *FixedType;
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} Binding;
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};
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Change() : Kind(ChangeKind::AddedTypeVariable), TypeVar(nullptr) { }
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/// Create a change that added a type variable.
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static Change addedTypeVariable(TypeVariableType *typeVar);
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/// Create a change that added a constraint.
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static Change addedConstraint(Constraint *constraint);
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/// Create a change that removed a constraint.
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static Change removedConstraint(Constraint *constraint);
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/// Create a change that extended an equivalence class.
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static Change extendedEquivalenceClass(TypeVariableType *typeVar,
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unsigned prevSize);
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/// Create a change that bound a type variable to a fixed type.
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static Change boundTypeVariable(TypeVariableType *typeVar, Type fixed);
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/// Undo this change, reverting the constraint graph to the state it
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/// had prior to this change.
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///
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/// Changes must be undone in stack order.
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void undo(ConstraintSystem &cs);
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};
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SolverTrail(ConstraintSystem &cs) : CS(cs) {}
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~SolverTrail();
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SolverTrail(const SolverTrail &) = delete;
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SolverTrail &operator=(const SolverTrail &) = delete;
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void recordChange(Change change);
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void dumpActiveScopeChanges(llvm::raw_ostream &out,
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unsigned indent = 0);
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unsigned size() const {
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return Changes.size();
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}
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void undo(unsigned toIndex);
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private:
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ConstraintSystem &CS;
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/// The list of changes made to this constraint system.
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std::vector<Change> Changes;
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friend class ConstraintGraphScope;
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};
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} // namespace constraints
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} // namespace swift
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#endif // SWIFT_SEMA_CSTRAIL_H

Diff for: ‎include/swift/Sema/ConstraintGraph.h

+2-76
Original file line numberDiff line numberDiff line change
@@ -216,6 +216,7 @@ class ConstraintGraphNode {
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friend class ConstraintGraph;
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friend class ConstraintSystem;
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friend class TypeVariableBinding;
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friend class SolverTrail;
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};
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/// A graph that describes the relationships among the various type variables
@@ -387,7 +388,6 @@ class ConstraintGraph {
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/// Print the graph.
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void print(ArrayRef<TypeVariableType *> typeVars, llvm::raw_ostream &out);
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void dump(llvm::raw_ostream &out);
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void dumpActiveScopeChanges(llvm::raw_ostream &out, unsigned indent = 0);
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// FIXME: Potentially side-effectful.
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SWIFT_DEBUG_HELPER(void dump());
@@ -440,86 +440,12 @@ class ConstraintGraph {
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/// to contract constraint graph edges.
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void incrementConstraintsPerContractionCounter();
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/// The kind of change made to the graph.
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enum class ChangeKind {
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/// Added a type variable.
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AddedTypeVariable,
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/// Added a new constraint.
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AddedConstraint,
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/// Removed an existing constraint
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RemovedConstraint,
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/// Extended the equivalence class of a type variable.
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ExtendedEquivalenceClass,
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/// Added a fixed binding for a type variable.
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BoundTypeVariable,
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};
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/// A change made to the constraint graph.
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///
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/// Each change can be undone (once, and in reverse order) by calling the
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/// undo() method.
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class Change {
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public:
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/// The kind of change.
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ChangeKind Kind;
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union {
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TypeVariableType *TypeVar;
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Constraint *TheConstraint;
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struct {
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/// The type variable whose equivalence class was extended.
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TypeVariableType *TypeVar;
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/// The previous size of the equivalence class.
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unsigned PrevSize;
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} EquivClass;
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struct {
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/// The type variable being bound to a fixed type.
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TypeVariableType *TypeVar;
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/// The fixed type to which the type variable was bound.
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TypeBase *FixedType;
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} Binding;
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};
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Change() : Kind(ChangeKind::AddedTypeVariable), TypeVar(nullptr) { }
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/// Create a change that added a type variable.
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static Change addedTypeVariable(TypeVariableType *typeVar);
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/// Create a change that added a constraint.
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static Change addedConstraint(Constraint *constraint);
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/// Create a change that removed a constraint.
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static Change removedConstraint(Constraint *constraint);
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/// Create a change that extended an equivalence class.
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static Change extendedEquivalenceClass(TypeVariableType *typeVar,
500-
unsigned prevSize);
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/// Create a change that bound a type variable to a fixed type.
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static Change boundTypeVariable(TypeVariableType *typeVar, Type fixed);
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/// Undo this change, reverting the constraint graph to the state it
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/// had prior to this change.
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///
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/// Changes must be undone in stack order.
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void undo(ConstraintGraph &cg);
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};
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/// The currently active scope, or null if we aren't tracking changes made
513444
/// to the constraint graph.
514445
ConstraintGraphScope *ActiveScope = nullptr;
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/// The set of changes made to this constraint graph.
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///
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/// As the constraint graph is extended and mutated, additional changes are
519-
/// introduced into this vector. Each scope
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llvm::SmallVector<Change, 4> Changes;
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522447
friend class ConstraintGraphScope;
448+
friend class SolverTrail;
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};
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525451
} // end namespace constraints

Diff for: ‎include/swift/Sema/ConstraintSystem.h

+9-2
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@@ -32,6 +32,7 @@
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#include "swift/Basic/OptionSet.h"
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#include "swift/Sema/CSBindings.h"
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#include "swift/Sema/CSFix.h"
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#include "swift/Sema/CSTrail.h"
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#include "swift/Sema/Constraint.h"
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#include "swift/Sema/ConstraintGraph.h"
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#include "swift/Sema/ConstraintGraphScope.h"
@@ -63,8 +64,6 @@ enum class TypeCheckExprFlags;
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namespace constraints {
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class ConstraintGraph;
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class ConstraintGraphNode;
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class ConstraintSystem;
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class SyntacticElementTarget;
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@@ -2533,6 +2532,10 @@ class ConstraintSystem {
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/// processing this constraint system.
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SavedTypeVariableBindings savedBindings;
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/// A log of changes to the constraint system, representing the
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/// current path being explored in the solution space.
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SolverTrail Trail;
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/// The best solution computed so far.
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std::optional<Score> BestScore;
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@@ -2681,6 +2684,10 @@ class ConstraintSystem {
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favoredConstraints.push_back(constraint);
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}
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void recordChange(SolverTrail::Change change) {
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Trail.recordChange(change);
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}
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private:
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/// The list of constraints that have been retired along the
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/// current path, this list is used in LIFO fashion when

Diff for: ‎lib/Sema/CMakeLists.txt

+1
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@@ -11,6 +11,7 @@ add_swift_host_library(swiftSema STATIC
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CSSimplify.cpp
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CSSolver.cpp
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CSStep.cpp
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CSTrail.cpp
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CSFix.cpp
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CSDiagnostics.cpp
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CodeSynthesis.cpp

Diff for: ‎lib/Sema/CSSolver.cpp

+1-1
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@@ -568,7 +568,7 @@ void truncate(llvm::SetVector<V> &vector, unsigned newSize) {
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569569
ConstraintSystem::SolverState::SolverState(
570570
ConstraintSystem &cs, FreeTypeVariableBinding allowFreeTypeVariables)
571-
: CS(cs), AllowFreeTypeVariables(allowFreeTypeVariables) {
571+
: CS(cs), AllowFreeTypeVariables(allowFreeTypeVariables), Trail(cs) {
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assert(!CS.solverState &&
573573
"Constraint system should not already have solver state!");
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CS.solverState = this;

Diff for: ‎lib/Sema/CSStep.h

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Original file line numberDiff line numberDiff line change
@@ -550,9 +550,8 @@ template <typename P> class BindingStep : public SolverStep {
550550
ActiveChoice.emplace(std::move(scope), *choice);
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552552
if (CS.isDebugMode()) {
553-
auto &log = llvm::errs();
554-
auto &CG = CS.getConstraintGraph();
555-
CG.dumpActiveScopeChanges(log, CS.solverState->getCurrentIndent());
553+
CS.solverState->Trail.dumpActiveScopeChanges(
554+
llvm::errs(), CS.solverState->getCurrentIndent());
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}
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558557
return suspend(std::make_unique<SplitterStep>(CS, Solutions));

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