clang  10.0.0svn
InterpStack.h
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1 //===--- InterpStack.h - Stack implementation for the VM --------*- 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 // Defines the upwards-growing stack used by the interpreter.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_CLANG_AST_INTERP_INTERPSTACK_H
14 #define LLVM_CLANG_AST_INTERP_INTERPSTACK_H
15 
16 #include <memory>
17 
18 namespace clang {
19 namespace interp {
20 
21 /// Stack frame storing temporaries and parameters.
22 class InterpStack final {
23 public:
25 
26  /// Destroys the stack, freeing up storage.
27  ~InterpStack();
28 
29  /// Constructs a value in place on the top of the stack.
30  template <typename T, typename... Tys> void push(Tys &&... Args) {
31  new (grow(aligned_size<T>())) T(std::forward<Tys>(Args)...);
32  }
33 
34  /// Returns the value from the top of the stack and removes it.
35  template <typename T> T pop() {
36  auto *Ptr = &peek<T>();
37  auto Value = std::move(*Ptr);
38  Ptr->~T();
39  shrink(aligned_size<T>());
40  return Value;
41  }
42 
43  /// Discards the top value from the stack.
44  template <typename T> void discard() {
45  auto *Ptr = &peek<T>();
46  Ptr->~T();
47  shrink(aligned_size<T>());
48  }
49 
50  /// Returns a reference to the value on the top of the stack.
51  template <typename T> T &peek() {
52  return *reinterpret_cast<T *>(peek(aligned_size<T>()));
53  }
54 
55  /// Returns a pointer to the top object.
56  void *top() { return Chunk ? peek(0) : nullptr; }
57 
58  /// Returns the size of the stack in bytes.
59  size_t size() const { return StackSize; }
60 
61  /// Clears the stack without calling any destructors.
62  void clear();
63 
64 private:
65  /// All stack slots are aligned to the native pointer alignment for storage.
66  /// The size of an object is rounded up to a pointer alignment multiple.
67  template <typename T> constexpr size_t aligned_size() const {
68  constexpr size_t PtrAlign = alignof(void *);
69  return ((sizeof(T) + PtrAlign - 1) / PtrAlign) * PtrAlign;
70  }
71 
72  /// Grows the stack to accomodate a value and returns a pointer to it.
73  void *grow(size_t Size);
74  /// Returns a pointer from the top of the stack.
75  void *peek(size_t Size);
76  /// Shrinks the stack.
77  void shrink(size_t Size);
78 
79  /// Allocate stack space in 1Mb chunks.
80  static constexpr size_t ChunkSize = 1024 * 1024;
81 
82  /// Metadata for each stack chunk.
83  ///
84  /// The stack is composed of a linked list of chunks. Whenever an allocation
85  /// is out of bounds, a new chunk is linked. When a chunk becomes empty,
86  /// it is not immediately freed: a chunk is deallocated only when the
87  /// predecessor becomes empty.
88  struct StackChunk {
89  StackChunk *Next;
90  StackChunk *Prev;
91  char *End;
92 
93  StackChunk(StackChunk *Prev = nullptr)
94  : Next(nullptr), Prev(Prev), End(reinterpret_cast<char *>(this + 1)) {}
95 
96  /// Returns the size of the chunk, minus the header.
97  size_t size() { return End - start(); }
98 
99  /// Returns a pointer to the start of the data region.
100  char *start() { return reinterpret_cast<char *>(this + 1); }
101  };
102  static_assert(sizeof(StackChunk) < ChunkSize, "Invalid chunk size");
103 
104  /// First chunk on the stack.
105  StackChunk *Chunk = nullptr;
106  /// Total size of the stack.
107  size_t StackSize = 0;
108 };
109 
110 } // namespace interp
111 } // namespace clang
112 
113 #endif
void clear()
Clears the stack without calling any destructors.
Definition: InterpStack.cpp:20
void * top()
Returns a pointer to the top object.
Definition: InterpStack.h:56
void push(Tys &&... Args)
Constructs a value in place on the top of the stack.
Definition: InterpStack.h:30
T pop()
Returns the value from the top of the stack and removes it.
Definition: InterpStack.h:35
Stack frame storing temporaries and parameters.
Definition: InterpStack.h:22
SourceLocation End
~InterpStack()
Destroys the stack, freeing up storage.
Definition: InterpStack.cpp:16
Dataflow Directional Tag Classes.
size_t size() const
Returns the size of the stack in bytes.
Definition: InterpStack.h:59
void discard()
Discards the top value from the stack.
Definition: InterpStack.h:44
T & peek()
Returns a reference to the value on the top of the stack.
Definition: InterpStack.h:51