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+//===--- InterpStack.h - Stack implementation for the VM --------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// Defines the upwards-growing stack used by the interpreter.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_AST_INTERP_INTERPSTACK_H
+#define LLVM_CLANG_AST_INTERP_INTERPSTACK_H
+
+#include <memory>
+
+namespace clang {
+namespace interp {
+
+/// Stack frame storing temporaries and parameters.
+class InterpStack final {
+public:
+ InterpStack() {}
+
+ /// Destroys the stack, freeing up storage.
+ ~InterpStack();
+
+ /// Constructs a value in place on the top of the stack.
+ template <typename T, typename... Tys> void push(Tys &&... Args) {
+ new (grow(aligned_size<T>())) T(std::forward<Tys>(Args)...);
+ }
+
+ /// Returns the value from the top of the stack and removes it.
+ template <typename T> T pop() {
+ auto *Ptr = &peek<T>();
+ auto Value = std::move(*Ptr);
+ Ptr->~T();
+ shrink(aligned_size<T>());
+ return Value;
+ }
+
+ /// Discards the top value from the stack.
+ template <typename T> void discard() {
+ auto *Ptr = &peek<T>();
+ Ptr->~T();
+ shrink(aligned_size<T>());
+ }
+
+ /// Returns a reference to the value on the top of the stack.
+ template <typename T> T &peek() {
+ return *reinterpret_cast<T *>(peek(aligned_size<T>()));
+ }
+
+ /// Returns a pointer to the top object.
+ void *top() { return Chunk ? peek(0) : nullptr; }
+
+ /// Returns the size of the stack in bytes.
+ size_t size() const { return StackSize; }
+
+ /// Clears the stack without calling any destructors.
+ void clear();
+
+private:
+ /// All stack slots are aligned to the native pointer alignment for storage.
+ /// The size of an object is rounded up to a pointer alignment multiple.
+ template <typename T> constexpr size_t aligned_size() const {
+ constexpr size_t PtrAlign = alignof(void *);
+ return ((sizeof(T) + PtrAlign - 1) / PtrAlign) * PtrAlign;
+ }
+
+ /// Grows the stack to accomodate a value and returns a pointer to it.
+ void *grow(size_t Size);
+ /// Returns a pointer from the top of the stack.
+ void *peek(size_t Size);
+ /// Shrinks the stack.
+ void shrink(size_t Size);
+
+ /// Allocate stack space in 1Mb chunks.
+ static constexpr size_t ChunkSize = 1024 * 1024;
+
+ /// Metadata for each stack chunk.
+ ///
+ /// The stack is composed of a linked list of chunks. Whenever an allocation
+ /// is out of bounds, a new chunk is linked. When a chunk becomes empty,
+ /// it is not immediately freed: a chunk is deallocated only when the
+ /// predecessor becomes empty.
+ struct StackChunk {
+ StackChunk *Next;
+ StackChunk *Prev;
+ char *End;
+
+ StackChunk(StackChunk *Prev = nullptr)
+ : Next(nullptr), Prev(Prev), End(reinterpret_cast<char *>(this + 1)) {}
+
+ /// Returns the size of the chunk, minus the header.
+ size_t size() { return End - start(); }
+
+ /// Returns a pointer to the start of the data region.
+ char *start() { return reinterpret_cast<char *>(this + 1); }
+ };
+ static_assert(sizeof(StackChunk) < ChunkSize, "Invalid chunk size");
+
+ /// First chunk on the stack.
+ StackChunk *Chunk = nullptr;
+ /// Total size of the stack.
+ size_t StackSize = 0;
+};
+
+} // namespace interp
+} // namespace clang
+
+#endif