c10/util/SmallVector.cpp

//===- llvm/ADT/SmallVector.cpp - 'Normally small' vectors ----------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements the SmallVector class.
//
//===----------------------------------------------------------------------===//

// ATen: modified from llvm::SmallVector.
// replaced llvm::safe_malloc with std::bad_alloc
// deleted LLVM_ENABLE_EXCEPTIONS

#include <c10/util/SmallVector.h>
#include <cstdint>
#include <stdexcept>
#include <string>
using namespace c10;

// Check that no bytes are wasted and everything is well-aligned.
namespace {
// These structures may cause binary compat warnings on AIX. Suppress the
// warning since we are only using these types for the static assertions below.
#if defined(_AIX)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Waix-compat"
#endif
struct Struct16B {
  alignas(16) void* X;
};
struct Struct32B {
  alignas(32) void* X;
};
#if defined(_AIX)
#pragma GCC diagnostic pop
#endif
} // namespace
static_assert(
    sizeof(SmallVector<void*, 0>) == sizeof(unsigned) * 2 + sizeof(void*),
    "wasted space in SmallVector size 0");
static_assert(
    alignof(SmallVector<Struct16B, 0>) >= alignof(Struct16B),
    "wrong alignment for 16-byte aligned T");
static_assert(
    alignof(SmallVector<Struct32B, 0>) >= alignof(Struct32B),
    "wrong alignment for 32-byte aligned T");
static_assert(
    sizeof(SmallVector<Struct16B, 0>) >= alignof(Struct16B),
    "missing padding for 16-byte aligned T");
static_assert(
    sizeof(SmallVector<Struct32B, 0>) >= alignof(Struct32B),
    "missing padding for 32-byte aligned T");
static_assert(
    sizeof(SmallVector<void*, 1>) == sizeof(unsigned) * 2 + sizeof(void*) * 2,
    "wasted space in SmallVector size 1");

static_assert(
    sizeof(SmallVector<char, 0>) == sizeof(void*) * 2 + sizeof(void*),
    "1 byte elements have word-sized type for size and capacity");

/// Report that MinSize doesn't fit into this vector's size type. Throws
/// std::length_error or calls report_fatal_error.
[[noreturn]] static void report_size_overflow(size_t MinSize, size_t MaxSize);
static void report_size_overflow(size_t MinSize, size_t MaxSize) {
  std::string Reason = "SmallVector unable to grow. Requested capacity (" +
      std::to_string(MinSize) +
      ") is larger than maximum value for size type (" +
      std::to_string(MaxSize) + ")";
  throw std::length_error(Reason);
}

/// Report that this vector is already at maximum capacity. Throws
/// std::length_error or calls report_fatal_error.
[[noreturn]] static void report_at_maximum_capacity(size_t MaxSize);
static void report_at_maximum_capacity(size_t MaxSize) {
  std::string Reason =
      "SmallVector capacity unable to grow. Already at maximum size " +
      std::to_string(MaxSize);
  throw std::length_error(Reason);
}

// Note: Moving this function into the header may cause performance regression.
template <class Size_T>
static size_t getNewCapacity(size_t MinSize, size_t TSize, size_t OldCapacity) {
  constexpr size_t MaxSize = std::numeric_limits<Size_T>::max();

  // Ensure we can fit the new capacity.
  // This is only going to be applicable when the capacity is 32 bit.
  if (MinSize > MaxSize)
    report_size_overflow(MinSize, MaxSize);

  // Ensure we can meet the guarantee of space for at least one more element.
  // The above check alone will not catch the case where grow is called with a
  // default MinSize of 0, but the current capacity cannot be increased.
  // This is only going to be applicable when the capacity is 32 bit.
  if (OldCapacity == MaxSize)
    report_at_maximum_capacity(MaxSize);

  // In theory 2*capacity can overflow if the capacity is 64 bit, but the
  // original capacity would never be large enough for this to be a problem.
  size_t NewCapacity = 2 * OldCapacity + 1; // Always grow.
  return std::min(std::max(NewCapacity, MinSize), MaxSize);
}

// Note: Moving this function into the header may cause performance regression.
template <class Size_T>
void* SmallVectorBase<Size_T>::mallocForGrow(
    size_t MinSize,
    size_t TSize,
    size_t& NewCapacity) {
  NewCapacity = getNewCapacity<Size_T>(MinSize, TSize, this->capacity());
  auto Result = std::malloc(NewCapacity * TSize);
  if (Result == nullptr) {
    throw std::bad_alloc();
  }
  return Result;
}

// Note: Moving this function into the header may cause performance regression.
template <class Size_T>
void SmallVectorBase<Size_T>::grow_pod(
    void* FirstEl,
    size_t MinSize,
    size_t TSize) {
  size_t NewCapacity = getNewCapacity<Size_T>(MinSize, TSize, this->capacity());
  void* NewElts = nullptr;
  if (BeginX == FirstEl) {
    NewElts = std::malloc(NewCapacity * TSize);
    if (NewElts == nullptr) {
      throw std::bad_alloc();
    }

    // Copy the elements over.  No need to run dtors on PODs.
    memcpy(NewElts, this->BeginX, size() * TSize);
  } else {
    // If this wasn't grown from the inline copy, grow the allocated space.
    NewElts = std::realloc(this->BeginX, NewCapacity * TSize);
    if (NewElts == nullptr) {
      throw std::bad_alloc();
    }
  }

  this->BeginX = NewElts;
  this->Capacity = NewCapacity;
}

template class c10::SmallVectorBase<uint32_t>;

// Disable the uint64_t instantiation for 32-bit builds.
// Both uint32_t and uint64_t instantiations are needed for 64-bit builds.
// This instantiation will never be used in 32-bit builds, and will cause
// warnings when sizeof(Size_T) > sizeof(size_t).
#if SIZE_MAX > UINT32_MAX
template class c10::SmallVectorBase<uint64_t>;

// Assertions to ensure this #if stays in sync with SmallVectorSizeType.
static_assert(
    sizeof(SmallVectorSizeType<char>) == sizeof(uint64_t),
    "Expected SmallVectorBase<uint64_t> variant to be in use.");
#else
static_assert(
    sizeof(SmallVectorSizeType<char>) == sizeof(uint32_t),
    "Expected SmallVectorBase<uint32_t> variant to be in use.");
#endif