1 //===- Ownership.h - Parser ownership helpers -------------------*- 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 //  This file contains classes for managing ownership of Stmt and Expr nodes.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_CLANG_SEMA_OWNERSHIP_H
14 #define LLVM_CLANG_SEMA_OWNERSHIP_H
15 
16 #include "clang/AST/Expr.h"
17 #include "clang/Basic/LLVM.h"
18 #include "llvm/ADT/ArrayRef.h"
19 #include "llvm/Support/PointerLikeTypeTraits.h"
20 #include "llvm/Support/type_traits.h"
21 #include <cassert>
22 #include <cstddef>
23 #include <cstdint>
24 
25 //===----------------------------------------------------------------------===//
26 // OpaquePtr
27 //===----------------------------------------------------------------------===//
28 
29 namespace clang {
30 
31 class CXXBaseSpecifier;
32 class CXXCtorInitializer;
33 class Decl;
34 class Expr;
35 class ParsedTemplateArgument;
36 class QualType;
37 class Stmt;
38 class TemplateName;
39 class TemplateParameterList;
40 
41   /// Wrapper for void* pointer.
42   /// \tparam PtrTy Either a pointer type like 'T*' or a type that behaves like
43   ///               a pointer.
44   ///
45   /// This is a very simple POD type that wraps a pointer that the Parser
46   /// doesn't know about but that Sema or another client does.  The PtrTy
47   /// template argument is used to make sure that "Decl" pointers are not
48   /// compatible with "Type" pointers for example.
49   template <class PtrTy>
50   class OpaquePtr {
51     void *Ptr = nullptr;
52 
53     explicit OpaquePtr(void *Ptr) : Ptr(Ptr) {}
54 
55     using Traits = llvm::PointerLikeTypeTraits<PtrTy>;
56 
57   public:
58     OpaquePtr(std::nullptr_t = nullptr) {}
59 
60     static OpaquePtr make(PtrTy P) { OpaquePtr OP; OP.set(P); return OP; }
61 
62     /// Returns plain pointer to the entity pointed by this wrapper.
63     /// \tparam PointeeT Type of pointed entity.
64     ///
65     /// It is identical to getPtrAs<PointeeT*>.
66     template <typename PointeeT> PointeeT* getPtrTo() const {
67       return get();
68     }
69 
70     /// Returns pointer converted to the specified type.
71     /// \tparam PtrT Result pointer type.  There must be implicit conversion
72     ///              from PtrTy to PtrT.
73     ///
74     /// In contrast to getPtrTo, this method allows the return type to be
75     /// a smart pointer.
76     template <typename PtrT> PtrT getPtrAs() const {
77       return get();
78     }
79 
80     PtrTy get() const {
81       return Traits::getFromVoidPointer(Ptr);
82     }
83 
84     void set(PtrTy P) {
85       Ptr = Traits::getAsVoidPointer(P);
86     }
87 
88     explicit operator bool() const { return Ptr != nullptr; }
89 
90     void *getAsOpaquePtr() const { return Ptr; }
91     static OpaquePtr getFromOpaquePtr(void *P) { return OpaquePtr(P); }
92   };
93 
94   /// UnionOpaquePtr - A version of OpaquePtr suitable for membership
95   /// in a union.
96   template <class T> struct UnionOpaquePtr {
97     void *Ptr;
98 
99     static UnionOpaquePtr make(OpaquePtr<T> P) {
100       UnionOpaquePtr OP = { P.getAsOpaquePtr() };
101       return OP;
102     }
103 
104     OpaquePtr<T> get() const { return OpaquePtr<T>::getFromOpaquePtr(Ptr); }
105     operator OpaquePtr<T>() const { return get(); }
106 
107     UnionOpaquePtr &operator=(OpaquePtr<T> P) {
108       Ptr = P.getAsOpaquePtr();
109       return *this;
110     }
111   };
112 
113 } // namespace clang
114 
115 namespace llvm {
116 
117   template <class T>
118   struct PointerLikeTypeTraits<clang::OpaquePtr<T>> {
119     static constexpr int NumLowBitsAvailable = 0;
120 
121     static inline void *getAsVoidPointer(clang::OpaquePtr<T> P) {
122       // FIXME: Doesn't work? return P.getAs< void >();
123       return P.getAsOpaquePtr();
124     }
125 
126     static inline clang::OpaquePtr<T> getFromVoidPointer(void *P) {
127       return clang::OpaquePtr<T>::getFromOpaquePtr(P);
128     }
129   };
130 
131 } // namespace llvm
132 
133 namespace clang {
134 
135   // Basic
136   class DiagnosticBuilder;
137 
138   // Determines whether the low bit of the result pointer for the
139   // given UID is always zero. If so, ActionResult will use that bit
140   // for it's "invalid" flag.
141   template<class Ptr>
142   struct IsResultPtrLowBitFree {
143     static const bool value = false;
144   };
145 
146   /// ActionResult - This structure is used while parsing/acting on
147   /// expressions, stmts, etc.  It encapsulates both the object returned by
148   /// the action, plus a sense of whether or not it is valid.
149   /// When CompressInvalid is true, the "invalid" flag will be
150   /// stored in the low bit of the Val pointer.
151   template<class PtrTy,
152            bool CompressInvalid = IsResultPtrLowBitFree<PtrTy>::value>
153   class ActionResult {
154     PtrTy Val;
155     bool Invalid;
156 
157   public:
158     ActionResult(bool Invalid = false) : Val(PtrTy()), Invalid(Invalid) {}
159     ActionResult(PtrTy val) : Val(val), Invalid(false) {}
160     ActionResult(const DiagnosticBuilder &) : Val(PtrTy()), Invalid(true) {}
161 
162     // These two overloads prevent void* -> bool conversions.
163     ActionResult(const void *) = delete;
164     ActionResult(volatile void *) = delete;
165 
166     bool isInvalid() const { return Invalid; }
167     bool isUsable() const { return !Invalid && Val; }
168     bool isUnset() const { return !Invalid && !Val; }
169 
170     PtrTy get() const { return Val; }
171     template <typename T> T *getAs() { return static_cast<T*>(get()); }
172 
173     void set(PtrTy V) { Val = V; }
174 
175     const ActionResult &operator=(PtrTy RHS) {
176       Val = RHS;
177       Invalid = false;
178       return *this;
179     }
180   };
181 
182   // This ActionResult partial specialization places the "invalid"
183   // flag into the low bit of the pointer.
184   template<typename PtrTy>
185   class ActionResult<PtrTy, true> {
186     // A pointer whose low bit is 1 if this result is invalid, 0
187     // otherwise.
188     uintptr_t PtrWithInvalid;
189 
190     using PtrTraits = llvm::PointerLikeTypeTraits<PtrTy>;
191 
192   public:
193     ActionResult(bool Invalid = false)
194         : PtrWithInvalid(static_cast<uintptr_t>(Invalid)) {}
195 
196     ActionResult(PtrTy V) {
197       void *VP = PtrTraits::getAsVoidPointer(V);
198       PtrWithInvalid = reinterpret_cast<uintptr_t>(VP);
199       assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer");
200     }
201 
202     ActionResult(const DiagnosticBuilder &) : PtrWithInvalid(0x01) {}
203 
204     // These two overloads prevent void* -> bool conversions.
205     ActionResult(const void *) = delete;
206     ActionResult(volatile void *) = delete;
207 
208     bool isInvalid() const { return PtrWithInvalid & 0x01; }
209     bool isUsable() const { return PtrWithInvalid > 0x01; }
210     bool isUnset() const { return PtrWithInvalid == 0; }
211 
212     PtrTy get() const {
213       void *VP = reinterpret_cast<void *>(PtrWithInvalid & ~0x01);
214       return PtrTraits::getFromVoidPointer(VP);
215     }
216 
217     template <typename T> T *getAs() { return static_cast<T*>(get()); }
218 
219     void set(PtrTy V) {
220       void *VP = PtrTraits::getAsVoidPointer(V);
221       PtrWithInvalid = reinterpret_cast<uintptr_t>(VP);
222       assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer");
223     }
224 
225     const ActionResult &operator=(PtrTy RHS) {
226       void *VP = PtrTraits::getAsVoidPointer(RHS);
227       PtrWithInvalid = reinterpret_cast<uintptr_t>(VP);
228       assert((PtrWithInvalid & 0x01) == 0 && "Badly aligned pointer");
229       return *this;
230     }
231 
232     // For types where we can fit a flag in with the pointer, provide
233     // conversions to/from pointer type.
234     static ActionResult getFromOpaquePointer(void *P) {
235       ActionResult Result;
236       Result.PtrWithInvalid = (uintptr_t)P;
237       return Result;
238     }
239     void *getAsOpaquePointer() const { return (void*)PtrWithInvalid; }
240   };
241 
242   /// An opaque type for threading parsed type information through the
243   /// parser.
244   using ParsedType = OpaquePtr<QualType>;
245   using UnionParsedType = UnionOpaquePtr<QualType>;
246 
247   // We can re-use the low bit of expression, statement, base, and
248   // member-initializer pointers for the "invalid" flag of
249   // ActionResult.
250   template<> struct IsResultPtrLowBitFree<Expr*> {
251     static const bool value = true;
252   };
253   template<> struct IsResultPtrLowBitFree<Stmt*> {
254     static const bool value = true;
255   };
256   template<> struct IsResultPtrLowBitFree<CXXBaseSpecifier*> {
257     static const bool value = true;
258   };
259   template<> struct IsResultPtrLowBitFree<CXXCtorInitializer*> {
260     static const bool value = true;
261   };
262 
263   using ExprResult = ActionResult<Expr *>;
264   using StmtResult = ActionResult<Stmt *>;
265   using TypeResult = ActionResult<ParsedType>;
266   using BaseResult = ActionResult<CXXBaseSpecifier *>;
267   using MemInitResult = ActionResult<CXXCtorInitializer *>;
268 
269   using DeclResult = ActionResult<Decl *>;
270   using ParsedTemplateTy = OpaquePtr<TemplateName>;
271   using UnionParsedTemplateTy = UnionOpaquePtr<TemplateName>;
272 
273   using MultiExprArg = MutableArrayRef<Expr *>;
274   using MultiStmtArg = MutableArrayRef<Stmt *>;
275   using ASTTemplateArgsPtr = MutableArrayRef<ParsedTemplateArgument>;
276   using MultiTypeArg = MutableArrayRef<ParsedType>;
277   using MultiTemplateParamsArg = MutableArrayRef<TemplateParameterList *>;
278 
279   inline ExprResult ExprError() { return ExprResult(true); }
280   inline StmtResult StmtError() { return StmtResult(true); }
281   inline TypeResult TypeError() { return TypeResult(true); }
282 
283   inline ExprResult ExprError(const DiagnosticBuilder&) { return ExprError(); }
284   inline StmtResult StmtError(const DiagnosticBuilder&) { return StmtError(); }
285 
286   inline ExprResult ExprEmpty() { return ExprResult(false); }
287   inline StmtResult StmtEmpty() { return StmtResult(false); }
288 
289   inline Expr *AssertSuccess(ExprResult R) {
290     assert(!R.isInvalid() && "operation was asserted to never fail!");
291     return R.get();
292   }
293 
294   inline Stmt *AssertSuccess(StmtResult R) {
295     assert(!R.isInvalid() && "operation was asserted to never fail!");
296     return R.get();
297   }
298 
299 } // namespace clang
300 
301 #endif // LLVM_CLANG_SEMA_OWNERSHIP_H
302