// Copyright 2018 the V8 project authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef V8_TORQUE_PARAMETER_DIFFERENCE_H_
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#define V8_TORQUE_PARAMETER_DIFFERENCE_H_
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#include <vector>
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#include "src/torque/types.h"
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namespace v8 {
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namespace internal {
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namespace torque {
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class ParameterDifference {
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public:
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ParameterDifference(const TypeVector& to, const TypeVector& from) {
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DCHECK_EQ(to.size(), from.size());
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for (size_t i = 0; i < to.size(); ++i) {
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AddParameter(to[i], from[i]);
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}
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}
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// An overload is selected if it is strictly better than all alternatives.
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// This means that it has to be strictly better in at least one parameter,
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// and better or equally good in all others.
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//
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// When comparing a pair of corresponding parameters of two overloads...
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// ... they are considered equally good if:
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// - They are equal.
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// - Both require some implicit conversion.
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// ... one is considered better if:
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// - It is a strict subtype of the other.
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// - It doesn't require an implicit conversion, while the other does.
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bool StrictlyBetterThan(const ParameterDifference& other) const {
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DCHECK_EQ(difference_.size(), other.difference_.size());
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bool better_parameter_found = false;
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for (size_t i = 0; i < difference_.size(); ++i) {
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base::Optional<const Type*> a = difference_[i];
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base::Optional<const Type*> b = other.difference_[i];
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if (a == b) {
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continue;
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} else if (a && b && a != b && (*a)->IsSubtypeOf(*b)) {
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DCHECK(!(*b)->IsSubtypeOf(*a));
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better_parameter_found = true;
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} else if (a && !b) {
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better_parameter_found = true;
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} else {
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return false;
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}
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}
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return better_parameter_found;
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}
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private:
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// Pointwise difference between call arguments and a signature.
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// {base::nullopt} means that an implicit conversion was necessary,
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// otherwise we store the supertype found in the signature.
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std::vector<base::Optional<const Type*>> difference_;
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void AddParameter(const Type* to, const Type* from) {
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if (from->IsSubtypeOf(to)) {
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difference_.push_back(to);
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} else if (IsAssignableFrom(to, from)) {
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difference_.push_back(base::nullopt);
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} else {
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UNREACHABLE();
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}
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}
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};
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} // namespace torque
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} // namespace internal
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} // namespace v8
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#endif // V8_TORQUE_PARAMETER_DIFFERENCE_H_
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