1//===- TypeSwitch.h - Switch functionality for RTTI casting -*- C++ -*-----===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8///
9/// \file
10/// This file implements the TypeSwitch template, which mimics a switch()
11/// statement whose cases are type names.
12///
13//===-----------------------------------------------------------------------===/
14
15#ifndef LLVM_ADT_TYPESWITCH_H
16#define LLVM_ADT_TYPESWITCH_H
17
18#include "llvm/ADT/STLExtras.h"
19#include "llvm/Support/Casting.h"
20#include <optional>
21
22namespace llvm {
23namespace detail {
24
25template <typename DerivedT, typename T> class TypeSwitchBase {
26public:
27 TypeSwitchBase(const T &value) : value(value) {}
28 TypeSwitchBase(TypeSwitchBase &&other) : value(other.value) {}
29 ~TypeSwitchBase() = default;
30
31 /// TypeSwitchBase is not copyable.
32 TypeSwitchBase(const TypeSwitchBase &) = delete;
33 void operator=(const TypeSwitchBase &) = delete;
34 void operator=(TypeSwitchBase &&other) = delete;
35
36 /// Invoke a case on the derived class with multiple case types.
37 template <typename CaseT, typename CaseT2, typename... CaseTs,
38 typename CallableT>
39 // This is marked always_inline and nodebug so it doesn't show up in stack
40 // traces at -O0 (or other optimization levels). Large TypeSwitch's are
41 // common, are equivalent to a switch, and don't add any value to stack
42 // traces.
43 LLVM_ATTRIBUTE_ALWAYS_INLINE LLVM_ATTRIBUTE_NODEBUG DerivedT &
44 Case(CallableT &&caseFn) {
45 DerivedT &derived = static_cast<DerivedT &>(*this);
46 return derived.template Case<CaseT>(caseFn)
47 .template Case<CaseT2, CaseTs...>(caseFn);
48 }
49
50 /// Invoke a case on the derived class, inferring the type of the Case from
51 /// the first input of the given callable.
52 /// Note: This inference rules for this overload are very simple: strip
53 /// pointers and references.
54 template <typename CallableT> DerivedT &Case(CallableT &&caseFn) {
55 using Traits = function_traits<std::decay_t<CallableT>>;
56 using CaseT = std::remove_cv_t<std::remove_pointer_t<
57 std::remove_reference_t<typename Traits::template arg_t<0>>>>;
58
59 DerivedT &derived = static_cast<DerivedT &>(*this);
60 return derived.template Case<CaseT>(std::forward<CallableT>(caseFn));
61 }
62
63protected:
64 /// Trait to check whether `ValueT` provides a 'dyn_cast' method with type
65 /// `CastT`.
66 template <typename ValueT, typename CastT>
67 using has_dyn_cast_t =
68 decltype(std::declval<ValueT &>().template dyn_cast<CastT>());
69
70 /// Attempt to dyn_cast the given `value` to `CastT`. This overload is
71 /// selected if `value` already has a suitable dyn_cast method.
72 template <typename CastT, typename ValueT>
73 static decltype(auto) castValue(
74 ValueT &&value,
75 std::enable_if_t<is_detected<has_dyn_cast_t, ValueT, CastT>::value> * =
76 nullptr) {
77 return value.template dyn_cast<CastT>();
78 }
79
80 /// Attempt to dyn_cast the given `value` to `CastT`. This overload is
81 /// selected if llvm::dyn_cast should be used.
82 template <typename CastT, typename ValueT>
83 static decltype(auto) castValue(
84 ValueT &&value,
85 std::enable_if_t<!is_detected<has_dyn_cast_t, ValueT, CastT>::value> * =
86 nullptr) {
87 return dyn_cast<CastT>(value);
88 }
89
90 /// The root value we are switching on.
91 const T value;
92};
93} // end namespace detail
94
95/// This class implements a switch-like dispatch statement for a value of 'T'
96/// using dyn_cast functionality. Each `Case<T>` takes a callable to be invoked
97/// if the root value isa<T>, the callable is invoked with the result of
98/// dyn_cast<T>() as a parameter.
99///
100/// Example:
101/// Operation *op = ...;
102/// LogicalResult result = TypeSwitch<Operation *, LogicalResult>(op)
103/// .Case<ConstantOp>([](ConstantOp op) { ... })
104/// .Default([](Operation *op) { ... });
105///
106template <typename T, typename ResultT = void>
107class TypeSwitch : public detail::TypeSwitchBase<TypeSwitch<T, ResultT>, T> {
108public:
109 using BaseT = detail::TypeSwitchBase<TypeSwitch<T, ResultT>, T>;
110 using BaseT::BaseT;
111 using BaseT::Case;
112 TypeSwitch(TypeSwitch &&other) = default;
113
114 /// Add a case on the given type.
115 template <typename CaseT, typename CallableT>
116 TypeSwitch<T, ResultT> &Case(CallableT &&caseFn) {
117 if (result)
118 return *this;
119
120 // Check to see if CaseT applies to 'value'.
121 if (auto caseValue = BaseT::template castValue<CaseT>(this->value))
122 result.emplace(caseFn(caseValue));
123 return *this;
124 }
125
126 /// As a default, invoke the given callable within the root value.
127 template <typename CallableT>
128 [[nodiscard]] ResultT Default(CallableT &&defaultFn) {
129 if (result)
130 return std::move(*result);
131 return defaultFn(this->value);
132 }
133 /// As a default, return the given value.
134 [[nodiscard]] ResultT Default(ResultT defaultResult) {
135 if (result)
136 return std::move(*result);
137 return defaultResult;
138 }
139
140 [[nodiscard]] operator ResultT() {
141 assert(result && "Fell off the end of a type-switch");
142 return std::move(*result);
143 }
144
145private:
146 /// The pointer to the result of this switch statement, once known,
147 /// null before that.
148 std::optional<ResultT> result;
149};
150
151/// Specialization of TypeSwitch for void returning callables.
152template <typename T>
153class TypeSwitch<T, void>
154 : public detail::TypeSwitchBase<TypeSwitch<T, void>, T> {
155public:
156 using BaseT = detail::TypeSwitchBase<TypeSwitch<T, void>, T>;
157 using BaseT::BaseT;
158 using BaseT::Case;
159 TypeSwitch(TypeSwitch &&other) = default;
160
161 /// Add a case on the given type.
162 template <typename CaseT, typename CallableT>
163 TypeSwitch<T, void> &Case(CallableT &&caseFn) {
164 if (foundMatch)
165 return *this;
166
167 // Check to see if any of the types apply to 'value'.
168 if (auto caseValue = BaseT::template castValue<CaseT>(this->value)) {
169 caseFn(caseValue);
170 foundMatch = true;
171 }
172 return *this;
173 }
174
175 /// As a default, invoke the given callable within the root value.
176 template <typename CallableT> void Default(CallableT &&defaultFn) {
177 if (!foundMatch)
178 defaultFn(this->value);
179 }
180
181private:
182 /// A flag detailing if we have already found a match.
183 bool foundMatch = false;
184};
185} // end namespace llvm
186
187#endif // LLVM_ADT_TYPESWITCH_H
188

source code of llvm/include/llvm/ADT/TypeSwitch.h