stdlib/public/runtime/Array.cpp

//===------------- Array.cpp - Swift Array Operations Support -------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// Implementations of the array runtime functions.
//
// arrayInitWithCopy(T *dest, T *src, size_t count, M* self)
// arrayInitWithTake(NoAlias|FrontToBack|BackToFront)(T *dest, T *src,
//                                                    size_t count, M* self)
// arrayAssignWithCopy(NoAlias|FrontToBack|BackToFront)(T *dest, T *src,
//                                                      size_t count, M* self)
// arrayAssignWithTake(T *dest, T *src, size_t count, M* self)
// arrayDestroy(T *dst, size_t count, M* self)
//
//===----------------------------------------------------------------------===//

#include "swift/Runtime/Config.h"
#include "swift/Runtime/HeapObject.h"
#include "swift/Runtime/Metadata.h"

using namespace swift;

namespace {
enum class ArrayCopy : unsigned {
  NoAlias = 0,
  FrontToBack = 1,
  BackToFront = 2
};

enum class ArraySource {
  Copy,
  Take
};

enum class ArrayDest {
  Init,
  Assign
};
} // end anonymous namespace.

static void array_pod_copy(ArrayCopy copyKind, OpaqueValue *dest,
                           OpaqueValue *src, size_t stride, size_t count) {
  if (copyKind == ArrayCopy::NoAlias) {
    memcpy(dest, src, stride * count);
    return;
  }

  assert(copyKind == ArrayCopy::FrontToBack ||
         copyKind == ArrayCopy::BackToFront);
  memmove(dest, src, stride * count);
}

namespace {
typedef OpaqueValue *(*const WitnessFunction)(OpaqueValue *, OpaqueValue *,
                                              const Metadata *);
}

template <ArrayDest destOp, ArraySource srcOp>
static WitnessFunction get_witness_function(const ValueWitnessTable *wtable) {
  if (destOp == ArrayDest::Init) {
    if (srcOp == ArraySource::Copy)
      return wtable->initializeWithCopy;
    else {
      assert(srcOp == ArraySource::Take);
      return wtable->initializeWithTake;
    }
  } else {
    assert(destOp == ArrayDest::Assign);
    if (srcOp == ArraySource::Copy) {
      return wtable->assignWithCopy;
    } else {
      assert(srcOp == ArraySource::Take);
      return wtable->assignWithTake;
    }
  }
}
template <ArrayDest destOp, ArraySource srcOp, ArrayCopy copyKind>
static void array_copy_operation(OpaqueValue *dest, OpaqueValue *src,
                                 size_t count, const Metadata *self) {
  if (count == 0)
    return;

  auto wtable = self->getValueWitnesses();
  auto stride = wtable->getStride();

  // If we are doing a copy we need PODness for a memcpy.
  if (srcOp == ArraySource::Copy) {
    auto isPOD = wtable->isPOD();
    if (isPOD) {
      array_pod_copy(copyKind, dest, src, stride, count);
      return;
    }
  } else {
    // Otherwise, we are doing a take and need bitwise takability for a copy.
    assert(srcOp == ArraySource::Take);
    auto isBitwiseTakable = wtable->isBitwiseTakable();
    if (isBitwiseTakable && (destOp == ArrayDest::Init || wtable->isPOD())) {
      array_pod_copy(copyKind, dest, src, stride, count);
      return;
    }
  }

  // Call the witness to do the copy.
  if (copyKind == ArrayCopy::NoAlias || copyKind == ArrayCopy::FrontToBack) {
    auto copy = get_witness_function<destOp, srcOp>(wtable);
    for (size_t i = 0; i < count; ++i) {
      auto offset = i * stride;
      auto *from = reinterpret_cast<OpaqueValue *>((char *)src + offset);
      auto *to = reinterpret_cast<OpaqueValue *>((char *)dest + offset);
      copy(to, from, self);
    }
    return;
  }

  // Back-to-front copy.
  assert(copyKind == ArrayCopy::BackToFront);
  assert(count != 0);

  auto copy = get_witness_function<destOp, srcOp>(wtable);
  size_t i = count;
  do {
    auto offset = --i * stride;
    auto *from = reinterpret_cast<OpaqueValue *>((char *)src + offset);
    auto *to = reinterpret_cast<OpaqueValue *>((char *)dest + offset);
    copy(to, from, self);
  } while (i != 0);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayInitWithCopy(OpaqueValue *dest, OpaqueValue *src, size_t count,
                             const Metadata *self) {
  array_copy_operation<ArrayDest::Init, ArraySource::Copy, ArrayCopy::NoAlias>(
      dest, src, count, self);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayInitWithTakeNoAlias(OpaqueValue *dest, OpaqueValue *src,
                                    size_t count, const Metadata *self) {
  array_copy_operation<ArrayDest::Init, ArraySource::Take, ArrayCopy::NoAlias>(
      dest, src, count, self);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayInitWithTakeFrontToBack(OpaqueValue *dest, OpaqueValue *src,
                                        size_t count, const Metadata *self) {
  array_copy_operation<ArrayDest::Init, ArraySource::Take,
                       ArrayCopy::FrontToBack>(dest, src, count, self);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayInitWithTakeBackToFront(OpaqueValue *dest, OpaqueValue *src,
                                        size_t count, const Metadata *self) {
  array_copy_operation<ArrayDest::Init, ArraySource::Take,
                       ArrayCopy::BackToFront>(dest, src, count, self);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayAssignWithCopyNoAlias(OpaqueValue *dest, OpaqueValue *src,
                                      size_t count, const Metadata *self) {
  array_copy_operation<ArrayDest::Assign, ArraySource::Copy,
                       ArrayCopy::NoAlias>(dest, src, count, self);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayAssignWithCopyFrontToBack(OpaqueValue *dest, OpaqueValue *src,
                                          size_t count, const Metadata *self) {
  array_copy_operation<ArrayDest::Assign, ArraySource::Copy,
                       ArrayCopy::FrontToBack>(dest, src, count, self);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayAssignWithCopyBackToFront(OpaqueValue *dest, OpaqueValue *src,
                                          size_t count, const Metadata *self) {
  array_copy_operation<ArrayDest::Assign, ArraySource::Copy,
                       ArrayCopy::BackToFront>(dest, src, count, self);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayAssignWithTake(OpaqueValue *dest, OpaqueValue *src,
                               size_t count, const Metadata *self) {
  array_copy_operation<ArrayDest::Assign, ArraySource::Take,
                       ArrayCopy::NoAlias>(dest, src, count, self);
}

SWIFT_RUNTIME_EXPORT
void swift_arrayDestroy(OpaqueValue *begin, size_t count, const Metadata *self) {
  if (count == 0)
    return;

  auto wtable = self->getValueWitnesses();

  // Nothing to do if the type is POD.
  if (wtable->isPOD())
    return;

  auto stride = wtable->getStride();
  for (size_t i = 0; i < count; ++i) {
    auto offset = i * stride;
    auto *obj = reinterpret_cast<OpaqueValue *>((char *)begin + offset);
    wtable->destroy(obj, self);
  }
}