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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 "PrimType.h"
#include <memory>
#include <vector>
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)...);
#ifndef NDEBUG
ItemTypes.push_back(toPrimType<T>());
#endif
}
/// Returns the value from the top of the stack and removes it.
template <typename T> T pop() {
#ifndef NDEBUG
assert(!ItemTypes.empty());
assert(ItemTypes.back() == toPrimType<T>());
ItemTypes.pop_back();
#endif
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() {
#ifndef NDEBUG
assert(ItemTypes.back() == toPrimType<T>());
ItemTypes.pop_back();
#endif
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() const {
return *reinterpret_cast<T *>(peek(aligned_size<T>()));
}
/// Returns a pointer to the top object.
void *top() const { 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();
// Returns whether the stack is empty.
bool empty() const { return StackSize == 0; }
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 accommodate 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) const;
/// 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() const { return End - start(); }
/// Returns a pointer to the start of the data region.
char *start() { return reinterpret_cast<char *>(this + 1); }
const char *start() const {
return reinterpret_cast<const 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;
#ifndef NDEBUG
/// vector recording the type of data we pushed into the stack.
std::vector<PrimType> ItemTypes;
template <typename T> static constexpr PrimType toPrimType() {
if constexpr (std::is_same_v<T, Pointer>)
return PT_Ptr;
else if constexpr (std::is_same_v<T, bool> ||
std::is_same_v<T, Boolean>)
return PT_Bool;
else if constexpr (std::is_same_v<T, int8_t> ||
std::is_same_v<T, Integral<8, true>>)
return PT_Sint8;
else if constexpr (std::is_same_v<T, uint8_t> ||
std::is_same_v<T, Integral<8, false>>)
return PT_Uint8;
else if constexpr (std::is_same_v<T, int16_t> ||
std::is_same_v<T, Integral<16, true>>)
return PT_Sint16;
else if constexpr (std::is_same_v<T, uint16_t> ||
std::is_same_v<T, Integral<16, false>>)
return PT_Uint16;
else if constexpr (std::is_same_v<T, int32_t> ||
std::is_same_v<T, Integral<32, true>>)
return PT_Sint32;
else if constexpr (std::is_same_v<T, uint32_t> ||
std::is_same_v<T, Integral<32, false>>)
return PT_Uint32;
else if constexpr (std::is_same_v<T, int64_t> ||
std::is_same_v<T, Integral<64, true>>)
return PT_Sint64;
else if constexpr (std::is_same_v<T, uint64_t> ||
std::is_same_v<T, Integral<64, false>>)
return PT_Uint64;
llvm_unreachable("unknown type push()'ed into InterpStack");
}
#endif
};
} // namespace interp
} // namespace clang
#endif
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