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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 for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// Defines the upwards-growing stack used by the interpreter.
#include <memory>
namespace clang {
namespace interp {
/// Stack frame storing temporaries and parameters.
class InterpStack final {
InterpStack() {}
/// Destroys the stack, freeing up storage.
/// 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);
return Value;
/// Discards the top value from the stack.
template <typename T> void discard() {
auto *Ptr = &peek<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();
/// 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