1 // Copyright 2020 the V8 project authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef V8_CODEGEN_ALIGNED_SLOT_ALLOCATOR_H_ 6 #define V8_CODEGEN_ALIGNED_SLOT_ALLOCATOR_H_ 7 8 #include "src/base/macros.h" 9 #include "src/base/platform/platform.h" 10 #include "src/common/globals.h" 11 12 namespace v8 { 13 namespace internal { 14 15 // An aligned slot allocator. Allocates groups of 1, 2, or 4 slots such that the 16 // first slot of the group is aligned to the group size. The allocator can also 17 // allocate unaligned groups of arbitrary size, and an align the number of slots 18 // to 1, 2, or 4 slots. The allocator tries to be as thrifty as possible by 19 // reusing alignment padding slots in subsequent smaller slot allocations. 20 class V8_EXPORT_PRIVATE AlignedSlotAllocator { 21 public: 22 // Slots are always multiples of pointer-sized units. 23 static constexpr int kSlotSize = kSystemPointerSize; 24 NumSlotsForWidth(int bytes)25 static int NumSlotsForWidth(int bytes) { 26 DCHECK_GT(bytes, 0); 27 return (bytes + kSlotSize - 1) / kSlotSize; 28 } 29 30 AlignedSlotAllocator() = default; 31 32 // Allocates |n| slots, where |n| must be 1, 2, or 4. Padding slots may be 33 // inserted for alignment. 34 // Returns the starting index of the slots, which is evenly divisible by |n|. 35 int Allocate(int n); 36 37 // Gets the starting index of the slots that would be returned by Allocate(n). 38 int NextSlot(int n) const; 39 40 // Allocates the given number of slots at the current end of the slot area, 41 // and returns the starting index of the slots. This resets any fragment 42 // slots, so subsequent allocations will be after the end of this one. 43 // AllocateUnaligned(0) can be used to partition the slot area, for example 44 // to make sure tagged values follow untagged values on a Frame. 45 int AllocateUnaligned(int n); 46 47 // Aligns the slot area so that future allocations begin at the alignment. 48 // Returns the number of slots needed to align the slot area. 49 int Align(int n); 50 51 // Returns the size of the slot area, in slots. This will be greater than any 52 // already allocated slot index. Size()53 int Size() const { return size_; } 54 55 private: 56 static constexpr int kInvalidSlot = -1; 57 IsValid(int slot)58 static bool IsValid(int slot) { return slot > kInvalidSlot; } 59 60 int next1_ = kInvalidSlot; 61 int next2_ = kInvalidSlot; 62 int next4_ = 0; 63 int size_ = 0; 64 65 DISALLOW_NEW_AND_DELETE() 66 }; 67 68 } // namespace internal 69 } // namespace v8 70 71 #endif // V8_CODEGEN_ALIGNED_SLOT_ALLOCATOR_H_ 72