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651 lines
21 KiB
651 lines
21 KiB
//===-- xray_segmented_array.h ---------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This file is a part of XRay, a dynamic runtime instrumentation system.
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//
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// Defines the implementation of a segmented array, with fixed-size segments
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// backing the segments.
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//
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//===----------------------------------------------------------------------===//
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#ifndef XRAY_SEGMENTED_ARRAY_H
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#define XRAY_SEGMENTED_ARRAY_H
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#include "sanitizer_common/sanitizer_allocator.h"
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#include "xray_allocator.h"
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#include "xray_utils.h"
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#include <cassert>
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#include <type_traits>
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#include <utility>
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namespace __xray {
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/// The Array type provides an interface similar to std::vector<...> but does
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/// not shrink in size. Once constructed, elements can be appended but cannot be
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/// removed. The implementation is heavily dependent on the contract provided by
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/// the Allocator type, in that all memory will be released when the Allocator
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/// is destroyed. When an Array is destroyed, it will destroy elements in the
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/// backing store but will not free the memory.
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template <class T> class Array {
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struct Segment {
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Segment *Prev;
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Segment *Next;
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char Data[1];
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};
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public:
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// Each segment of the array will be laid out with the following assumptions:
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//
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// - Each segment will be on a cache-line address boundary (kCacheLineSize
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// aligned).
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//
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// - The elements will be accessed through an aligned pointer, dependent on
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// the alignment of T.
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//
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// - Each element is at least two-pointers worth from the beginning of the
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// Segment, aligned properly, and the rest of the elements are accessed
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// through appropriate alignment.
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//
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// We then compute the size of the segment to follow this logic:
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//
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// - Compute the number of elements that can fit within
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// kCacheLineSize-multiple segments, minus the size of two pointers.
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//
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// - Request cacheline-multiple sized elements from the allocator.
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static constexpr uint64_t AlignedElementStorageSize =
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sizeof(typename std::aligned_storage<sizeof(T), alignof(T)>::type);
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static constexpr uint64_t SegmentControlBlockSize = sizeof(Segment *) * 2;
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static constexpr uint64_t SegmentSize = nearest_boundary(
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SegmentControlBlockSize + next_pow2(sizeof(T)), kCacheLineSize);
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using AllocatorType = Allocator<SegmentSize>;
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static constexpr uint64_t ElementsPerSegment =
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(SegmentSize - SegmentControlBlockSize) / next_pow2(sizeof(T));
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static_assert(ElementsPerSegment > 0,
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"Must have at least 1 element per segment.");
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static Segment SentinelSegment;
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using size_type = uint64_t;
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private:
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// This Iterator models a BidirectionalIterator.
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template <class U> class Iterator {
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Segment *S = &SentinelSegment;
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uint64_t Offset = 0;
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uint64_t Size = 0;
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public:
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Iterator(Segment *IS, uint64_t Off, uint64_t S) XRAY_NEVER_INSTRUMENT
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: S(IS),
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Offset(Off),
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Size(S) {}
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Iterator(const Iterator &) NOEXCEPT XRAY_NEVER_INSTRUMENT = default;
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Iterator() NOEXCEPT XRAY_NEVER_INSTRUMENT = default;
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Iterator(Iterator &&) NOEXCEPT XRAY_NEVER_INSTRUMENT = default;
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Iterator &operator=(const Iterator &) XRAY_NEVER_INSTRUMENT = default;
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Iterator &operator=(Iterator &&) XRAY_NEVER_INSTRUMENT = default;
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~Iterator() XRAY_NEVER_INSTRUMENT = default;
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Iterator &operator++() XRAY_NEVER_INSTRUMENT {
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if (++Offset % ElementsPerSegment || Offset == Size)
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return *this;
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// At this point, we know that Offset % N == 0, so we must advance the
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// segment pointer.
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DCHECK_EQ(Offset % ElementsPerSegment, 0);
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DCHECK_NE(Offset, Size);
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DCHECK_NE(S, &SentinelSegment);
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DCHECK_NE(S->Next, &SentinelSegment);
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S = S->Next;
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DCHECK_NE(S, &SentinelSegment);
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return *this;
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}
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Iterator &operator--() XRAY_NEVER_INSTRUMENT {
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DCHECK_NE(S, &SentinelSegment);
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DCHECK_GT(Offset, 0);
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auto PreviousOffset = Offset--;
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if (PreviousOffset != Size && PreviousOffset % ElementsPerSegment == 0) {
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DCHECK_NE(S->Prev, &SentinelSegment);
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S = S->Prev;
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}
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return *this;
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}
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Iterator operator++(int) XRAY_NEVER_INSTRUMENT {
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Iterator Copy(*this);
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++(*this);
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return Copy;
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}
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Iterator operator--(int) XRAY_NEVER_INSTRUMENT {
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Iterator Copy(*this);
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--(*this);
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return Copy;
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}
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template <class V, class W>
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friend bool operator==(const Iterator<V> &L,
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const Iterator<W> &R) XRAY_NEVER_INSTRUMENT {
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return L.S == R.S && L.Offset == R.Offset;
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}
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template <class V, class W>
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friend bool operator!=(const Iterator<V> &L,
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const Iterator<W> &R) XRAY_NEVER_INSTRUMENT {
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return !(L == R);
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}
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U &operator*() const XRAY_NEVER_INSTRUMENT {
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DCHECK_NE(S, &SentinelSegment);
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auto RelOff = Offset % ElementsPerSegment;
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// We need to compute the character-aligned pointer, offset from the
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// segment's Data location to get the element in the position of Offset.
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auto Base = &S->Data;
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auto AlignedOffset = Base + (RelOff * AlignedElementStorageSize);
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return *reinterpret_cast<U *>(AlignedOffset);
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}
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U *operator->() const XRAY_NEVER_INSTRUMENT { return &(**this); }
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};
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AllocatorType *Alloc;
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Segment *Head;
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Segment *Tail;
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// Here we keep track of segments in the freelist, to allow us to re-use
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// segments when elements are trimmed off the end.
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Segment *Freelist;
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uint64_t Size;
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// ===============================
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// In the following implementation, we work through the algorithms and the
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// list operations using the following notation:
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//
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// - pred(s) is the predecessor (previous node accessor) and succ(s) is
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// the successor (next node accessor).
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//
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// - S is a sentinel segment, which has the following property:
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//
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// pred(S) == succ(S) == S
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//
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// - @ is a loop operator, which can imply pred(s) == s if it appears on
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// the left of s, or succ(s) == S if it appears on the right of s.
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//
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// - sL <-> sR : means a bidirectional relation between sL and sR, which
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// means:
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//
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// succ(sL) == sR && pred(SR) == sL
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//
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// - sL -> sR : implies a unidirectional relation between sL and SR,
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// with the following properties:
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//
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// succ(sL) == sR
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//
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// sL <- sR : implies a unidirectional relation between sR and sL,
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// with the following properties:
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//
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// pred(sR) == sL
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//
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// ===============================
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Segment *NewSegment() XRAY_NEVER_INSTRUMENT {
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// We need to handle the case in which enough elements have been trimmed to
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// allow us to re-use segments we've allocated before. For this we look into
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// the Freelist, to see whether we need to actually allocate new blocks or
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// just re-use blocks we've already seen before.
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if (Freelist != &SentinelSegment) {
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// The current state of lists resemble something like this at this point:
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//
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// Freelist: @S@<-f0->...<->fN->@S@
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// ^ Freelist
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//
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// We want to perform a splice of `f0` from Freelist to a temporary list,
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// which looks like:
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//
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// Templist: @S@<-f0->@S@
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// ^ FreeSegment
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//
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// Our algorithm preconditions are:
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DCHECK_EQ(Freelist->Prev, &SentinelSegment);
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// Then the algorithm we implement is:
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//
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// SFS = Freelist
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// Freelist = succ(Freelist)
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// if (Freelist != S)
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// pred(Freelist) = S
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// succ(SFS) = S
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// pred(SFS) = S
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//
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auto *FreeSegment = Freelist;
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Freelist = Freelist->Next;
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// Note that we need to handle the case where Freelist is now pointing to
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// S, which we don't want to be overwriting.
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// TODO: Determine whether the cost of the branch is higher than the cost
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// of the blind assignment.
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if (Freelist != &SentinelSegment)
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Freelist->Prev = &SentinelSegment;
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FreeSegment->Next = &SentinelSegment;
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FreeSegment->Prev = &SentinelSegment;
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// Our postconditions are:
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DCHECK_EQ(Freelist->Prev, &SentinelSegment);
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DCHECK_NE(FreeSegment, &SentinelSegment);
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return FreeSegment;
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}
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auto SegmentBlock = Alloc->Allocate();
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if (SegmentBlock.Data == nullptr)
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return nullptr;
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// Placement-new the Segment element at the beginning of the SegmentBlock.
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new (SegmentBlock.Data) Segment{&SentinelSegment, &SentinelSegment, {0}};
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auto SB = reinterpret_cast<Segment *>(SegmentBlock.Data);
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return SB;
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}
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Segment *InitHeadAndTail() XRAY_NEVER_INSTRUMENT {
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DCHECK_EQ(Head, &SentinelSegment);
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DCHECK_EQ(Tail, &SentinelSegment);
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auto S = NewSegment();
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if (S == nullptr)
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return nullptr;
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DCHECK_EQ(S->Next, &SentinelSegment);
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DCHECK_EQ(S->Prev, &SentinelSegment);
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DCHECK_NE(S, &SentinelSegment);
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Head = S;
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Tail = S;
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DCHECK_EQ(Head, Tail);
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DCHECK_EQ(Tail->Next, &SentinelSegment);
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DCHECK_EQ(Tail->Prev, &SentinelSegment);
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return S;
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}
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Segment *AppendNewSegment() XRAY_NEVER_INSTRUMENT {
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auto S = NewSegment();
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if (S == nullptr)
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return nullptr;
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DCHECK_NE(Tail, &SentinelSegment);
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DCHECK_EQ(Tail->Next, &SentinelSegment);
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DCHECK_EQ(S->Prev, &SentinelSegment);
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DCHECK_EQ(S->Next, &SentinelSegment);
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S->Prev = Tail;
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Tail->Next = S;
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Tail = S;
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DCHECK_EQ(S, S->Prev->Next);
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DCHECK_EQ(Tail->Next, &SentinelSegment);
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return S;
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}
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public:
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explicit Array(AllocatorType &A) XRAY_NEVER_INSTRUMENT
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: Alloc(&A),
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Head(&SentinelSegment),
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Tail(&SentinelSegment),
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Freelist(&SentinelSegment),
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Size(0) {}
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Array() XRAY_NEVER_INSTRUMENT : Alloc(nullptr),
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Head(&SentinelSegment),
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Tail(&SentinelSegment),
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Freelist(&SentinelSegment),
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Size(0) {}
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Array(const Array &) = delete;
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Array &operator=(const Array &) = delete;
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Array(Array &&O) XRAY_NEVER_INSTRUMENT : Alloc(O.Alloc),
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Head(O.Head),
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Tail(O.Tail),
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Freelist(O.Freelist),
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Size(O.Size) {
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O.Alloc = nullptr;
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O.Head = &SentinelSegment;
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O.Tail = &SentinelSegment;
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O.Size = 0;
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O.Freelist = &SentinelSegment;
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}
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Array &operator=(Array &&O) XRAY_NEVER_INSTRUMENT {
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Alloc = O.Alloc;
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O.Alloc = nullptr;
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Head = O.Head;
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O.Head = &SentinelSegment;
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Tail = O.Tail;
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O.Tail = &SentinelSegment;
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Freelist = O.Freelist;
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O.Freelist = &SentinelSegment;
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Size = O.Size;
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O.Size = 0;
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return *this;
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}
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~Array() XRAY_NEVER_INSTRUMENT {
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for (auto &E : *this)
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(&E)->~T();
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}
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bool empty() const XRAY_NEVER_INSTRUMENT { return Size == 0; }
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AllocatorType &allocator() const XRAY_NEVER_INSTRUMENT {
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DCHECK_NE(Alloc, nullptr);
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return *Alloc;
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}
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uint64_t size() const XRAY_NEVER_INSTRUMENT { return Size; }
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template <class... Args>
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T *AppendEmplace(Args &&... args) XRAY_NEVER_INSTRUMENT {
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DCHECK((Size == 0 && Head == &SentinelSegment && Head == Tail) ||
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(Size != 0 && Head != &SentinelSegment && Tail != &SentinelSegment));
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if (UNLIKELY(Head == &SentinelSegment)) {
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auto R = InitHeadAndTail();
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if (R == nullptr)
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return nullptr;
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}
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DCHECK_NE(Head, &SentinelSegment);
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DCHECK_NE(Tail, &SentinelSegment);
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auto Offset = Size % ElementsPerSegment;
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if (UNLIKELY(Size != 0 && Offset == 0))
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if (AppendNewSegment() == nullptr)
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return nullptr;
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DCHECK_NE(Tail, &SentinelSegment);
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auto Base = &Tail->Data;
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auto AlignedOffset = Base + (Offset * AlignedElementStorageSize);
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DCHECK_LE(AlignedOffset + sizeof(T),
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reinterpret_cast<unsigned char *>(Base) + SegmentSize);
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// In-place construct at Position.
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new (AlignedOffset) T{std::forward<Args>(args)...};
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++Size;
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return reinterpret_cast<T *>(AlignedOffset);
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}
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T *Append(const T &E) XRAY_NEVER_INSTRUMENT {
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// FIXME: This is a duplication of AppenEmplace with the copy semantics
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// explicitly used, as a work-around to GCC 4.8 not invoking the copy
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// constructor with the placement new with braced-init syntax.
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DCHECK((Size == 0 && Head == &SentinelSegment && Head == Tail) ||
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(Size != 0 && Head != &SentinelSegment && Tail != &SentinelSegment));
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if (UNLIKELY(Head == &SentinelSegment)) {
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auto R = InitHeadAndTail();
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if (R == nullptr)
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return nullptr;
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}
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DCHECK_NE(Head, &SentinelSegment);
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DCHECK_NE(Tail, &SentinelSegment);
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auto Offset = Size % ElementsPerSegment;
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if (UNLIKELY(Size != 0 && Offset == 0))
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if (AppendNewSegment() == nullptr)
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return nullptr;
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DCHECK_NE(Tail, &SentinelSegment);
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auto Base = &Tail->Data;
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auto AlignedOffset = Base + (Offset * AlignedElementStorageSize);
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DCHECK_LE(AlignedOffset + sizeof(T),
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reinterpret_cast<unsigned char *>(Tail) + SegmentSize);
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// In-place construct at Position.
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new (AlignedOffset) T(E);
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++Size;
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return reinterpret_cast<T *>(AlignedOffset);
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}
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T &operator[](uint64_t Offset) const XRAY_NEVER_INSTRUMENT {
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DCHECK_LE(Offset, Size);
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// We need to traverse the array enough times to find the element at Offset.
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auto S = Head;
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while (Offset >= ElementsPerSegment) {
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S = S->Next;
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Offset -= ElementsPerSegment;
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DCHECK_NE(S, &SentinelSegment);
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}
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auto Base = &S->Data;
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auto AlignedOffset = Base + (Offset * AlignedElementStorageSize);
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auto Position = reinterpret_cast<T *>(AlignedOffset);
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return *reinterpret_cast<T *>(Position);
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}
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T &front() const XRAY_NEVER_INSTRUMENT {
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DCHECK_NE(Head, &SentinelSegment);
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DCHECK_NE(Size, 0u);
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return *begin();
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}
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T &back() const XRAY_NEVER_INSTRUMENT {
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DCHECK_NE(Tail, &SentinelSegment);
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DCHECK_NE(Size, 0u);
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auto It = end();
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--It;
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return *It;
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}
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template <class Predicate>
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T *find_element(Predicate P) const XRAY_NEVER_INSTRUMENT {
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if (empty())
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return nullptr;
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auto E = end();
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for (auto I = begin(); I != E; ++I)
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if (P(*I))
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return &(*I);
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return nullptr;
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}
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/// Remove N Elements from the end. This leaves the blocks behind, and not
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/// require allocation of new blocks for new elements added after trimming.
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void trim(uint64_t Elements) XRAY_NEVER_INSTRUMENT {
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auto OldSize = Size;
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Elements = Elements > Size ? Size : Elements;
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Size -= Elements;
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// We compute the number of segments we're going to return from the tail by
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// counting how many elements have been trimmed. Given the following:
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//
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// - Each segment has N valid positions, where N > 0
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// - The previous size > current size
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//
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// To compute the number of segments to return, we need to perform the
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// following calculations for the number of segments required given 'x'
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// elements:
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//
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// f(x) = {
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// x == 0 : 0
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// , 0 < x <= N : 1
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// , N < x <= max : x / N + (x % N ? 1 : 0)
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// }
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//
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// We can simplify this down to:
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//
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// f(x) = {
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// x == 0 : 0,
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// , 0 < x <= max : x / N + (x < N || x % N ? 1 : 0)
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// }
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//
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// And further down to:
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//
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// f(x) = x ? x / N + (x < N || x % N ? 1 : 0) : 0
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//
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// We can then perform the following calculation `s` which counts the number
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// of segments we need to remove from the end of the data structure:
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//
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// s(p, c) = f(p) - f(c)
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//
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// If we treat p = previous size, and c = current size, and given the
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// properties above, the possible range for s(...) is [0..max(typeof(p))/N]
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// given that typeof(p) == typeof(c).
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auto F = [](uint64_t X) {
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return X ? (X / ElementsPerSegment) +
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(X < ElementsPerSegment || X % ElementsPerSegment ? 1 : 0)
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: 0;
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};
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auto PS = F(OldSize);
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auto CS = F(Size);
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DCHECK_GE(PS, CS);
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auto SegmentsToTrim = PS - CS;
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for (auto I = 0uL; I < SegmentsToTrim; ++I) {
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|
// Here we place the current tail segment to the freelist. To do this
|
|
// appropriately, we need to perform a splice operation on two
|
|
// bidirectional linked-lists. In particular, we have the current state of
|
|
// the doubly-linked list of segments:
|
|
//
|
|
// @S@ <- s0 <-> s1 <-> ... <-> sT -> @S@
|
|
//
|
|
DCHECK_NE(Head, &SentinelSegment);
|
|
DCHECK_NE(Tail, &SentinelSegment);
|
|
DCHECK_EQ(Tail->Next, &SentinelSegment);
|
|
|
|
if (Freelist == &SentinelSegment) {
|
|
// Our two lists at this point are in this configuration:
|
|
//
|
|
// Freelist: (potentially) @S@
|
|
// Mainlist: @S@<-s0<->s1<->...<->sPT<->sT->@S@
|
|
// ^ Head ^ Tail
|
|
//
|
|
// The end state for us will be this configuration:
|
|
//
|
|
// Freelist: @S@<-sT->@S@
|
|
// Mainlist: @S@<-s0<->s1<->...<->sPT->@S@
|
|
// ^ Head ^ Tail
|
|
//
|
|
// The first step for us is to hold a reference to the tail of Mainlist,
|
|
// which in our notation is represented by sT. We call this our "free
|
|
// segment" which is the segment we are placing on the Freelist.
|
|
//
|
|
// sF = sT
|
|
//
|
|
// Then, we also hold a reference to the "pre-tail" element, which we
|
|
// call sPT:
|
|
//
|
|
// sPT = pred(sT)
|
|
//
|
|
// We want to splice sT into the beginning of the Freelist, which in
|
|
// an empty Freelist means placing a segment whose predecessor and
|
|
// successor is the sentinel segment.
|
|
//
|
|
// The splice operation then can be performed in the following
|
|
// algorithm:
|
|
//
|
|
// succ(sPT) = S
|
|
// pred(sT) = S
|
|
// succ(sT) = Freelist
|
|
// Freelist = sT
|
|
// Tail = sPT
|
|
//
|
|
auto SPT = Tail->Prev;
|
|
SPT->Next = &SentinelSegment;
|
|
Tail->Prev = &SentinelSegment;
|
|
Tail->Next = Freelist;
|
|
Freelist = Tail;
|
|
Tail = SPT;
|
|
|
|
// Our post-conditions here are:
|
|
DCHECK_EQ(Tail->Next, &SentinelSegment);
|
|
DCHECK_EQ(Freelist->Prev, &SentinelSegment);
|
|
} else {
|
|
// In the other case, where the Freelist is not empty, we perform the
|
|
// following transformation instead:
|
|
//
|
|
// This transforms the current state:
|
|
//
|
|
// Freelist: @S@<-f0->@S@
|
|
// ^ Freelist
|
|
// Mainlist: @S@<-s0<->s1<->...<->sPT<->sT->@S@
|
|
// ^ Head ^ Tail
|
|
//
|
|
// Into the following:
|
|
//
|
|
// Freelist: @S@<-sT<->f0->@S@
|
|
// ^ Freelist
|
|
// Mainlist: @S@<-s0<->s1<->...<->sPT->@S@
|
|
// ^ Head ^ Tail
|
|
//
|
|
// The algorithm is:
|
|
//
|
|
// sFH = Freelist
|
|
// sPT = pred(sT)
|
|
// pred(SFH) = sT
|
|
// succ(sT) = Freelist
|
|
// pred(sT) = S
|
|
// succ(sPT) = S
|
|
// Tail = sPT
|
|
// Freelist = sT
|
|
//
|
|
auto SFH = Freelist;
|
|
auto SPT = Tail->Prev;
|
|
auto ST = Tail;
|
|
SFH->Prev = ST;
|
|
ST->Next = Freelist;
|
|
ST->Prev = &SentinelSegment;
|
|
SPT->Next = &SentinelSegment;
|
|
Tail = SPT;
|
|
Freelist = ST;
|
|
|
|
// Our post-conditions here are:
|
|
DCHECK_EQ(Tail->Next, &SentinelSegment);
|
|
DCHECK_EQ(Freelist->Prev, &SentinelSegment);
|
|
DCHECK_EQ(Freelist->Next->Prev, Freelist);
|
|
}
|
|
}
|
|
|
|
// Now in case we've spliced all the segments in the end, we ensure that the
|
|
// main list is "empty", or both the head and tail pointing to the sentinel
|
|
// segment.
|
|
if (Tail == &SentinelSegment)
|
|
Head = Tail;
|
|
|
|
DCHECK(
|
|
(Size == 0 && Head == &SentinelSegment && Tail == &SentinelSegment) ||
|
|
(Size != 0 && Head != &SentinelSegment && Tail != &SentinelSegment));
|
|
DCHECK(
|
|
(Freelist != &SentinelSegment && Freelist->Prev == &SentinelSegment) ||
|
|
(Freelist == &SentinelSegment && Tail->Next == &SentinelSegment));
|
|
}
|
|
|
|
// Provide iterators.
|
|
Iterator<T> begin() const XRAY_NEVER_INSTRUMENT {
|
|
return Iterator<T>(Head, 0, Size);
|
|
}
|
|
Iterator<T> end() const XRAY_NEVER_INSTRUMENT {
|
|
return Iterator<T>(Tail, Size, Size);
|
|
}
|
|
Iterator<const T> cbegin() const XRAY_NEVER_INSTRUMENT {
|
|
return Iterator<const T>(Head, 0, Size);
|
|
}
|
|
Iterator<const T> cend() const XRAY_NEVER_INSTRUMENT {
|
|
return Iterator<const T>(Tail, Size, Size);
|
|
}
|
|
};
|
|
|
|
// We need to have this storage definition out-of-line so that the compiler can
|
|
// ensure that storage for the SentinelSegment is defined and has a single
|
|
// address.
|
|
template <class T>
|
|
typename Array<T>::Segment Array<T>::SentinelSegment{
|
|
&Array<T>::SentinelSegment, &Array<T>::SentinelSegment, {'\0'}};
|
|
|
|
} // namespace __xray
|
|
|
|
#endif // XRAY_SEGMENTED_ARRAY_H
|