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// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_CODEGEN_ALIGNED_SLOT_ALLOCATOR_H_
#define V8_CODEGEN_ALIGNED_SLOT_ALLOCATOR_H_
#include "src/base/macros.h"
#include "src/base/platform/platform.h"
#include "src/common/globals.h"
namespace v8 {
namespace internal {
// An aligned slot allocator. Allocates groups of 1, 2, or 4 slots such that the
// first slot of the group is aligned to the group size. The allocator can also
// allocate unaligned groups of arbitrary size, and an align the number of slots
// to 1, 2, or 4 slots. The allocator tries to be as thrifty as possible by
// reusing alignment padding slots in subsequent smaller slot allocations.
class V8_EXPORT_PRIVATE AlignedSlotAllocator {
public:
// Slots are always multiples of pointer-sized units.
static constexpr int kSlotSize = kSystemPointerSize;
static int NumSlotsForWidth(int bytes) {
DCHECK_GT(bytes, 0);
return (bytes + kSlotSize - 1) / kSlotSize;
}
AlignedSlotAllocator() = default;
// Allocates |n| slots, where |n| must be 1, 2, or 4. Padding slots may be
// inserted for alignment.
// Returns the starting index of the slots, which is evenly divisible by |n|.
int Allocate(int n);
// Gets the starting index of the slots that would be returned by Allocate(n).
int NextSlot(int n) const;
// Allocates the given number of slots at the current end of the slot area,
// and returns the starting index of the slots. This resets any fragment
// slots, so subsequent allocations will be after the end of this one.
// AllocateUnaligned(0) can be used to partition the slot area, for example
// to make sure tagged values follow untagged values on a Frame.
int AllocateUnaligned(int n);
// Aligns the slot area so that future allocations begin at the alignment.
// Returns the number of slots needed to align the slot area.
int Align(int n);
// Returns the size of the slot area, in slots. This will be greater than any
// already allocated slot index.
int Size() const { return size_; }
private:
static constexpr int kInvalidSlot = -1;
static bool IsValid(int slot) { return slot > kInvalidSlot; }
int next1_ = kInvalidSlot;
int next2_ = kInvalidSlot;
int next4_ = 0;
int size_ = 0;
DISALLOW_NEW_AND_DELETE()
};
} // namespace internal
} // namespace v8
#endif // V8_CODEGEN_ALIGNED_SLOT_ALLOCATOR_H_
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