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https://gitlab.kitware.com/vtk/vtk-m
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c029ac113d
For several versions, VTK-m has had a `Variant` templated class. This acts like a templated union where the object will store one of a list of types specified as the template arguments. (There are actually 2 versions for the control and execution environments, respectively.) Because this is a complex class that required several iterations to work through performance and compiler issues, `Variant` was placed in the `internal` namespace to avoid complications with backward compatibility. However, the class has been stable for a while, so let us expose this helpful tool for wider use.
356 lines
12 KiB
C
356 lines
12 KiB
C
//============================================================================
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// Copyright (c) Kitware, Inc.
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// All rights reserved.
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// See LICENSE.txt for details.
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//
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// This software is distributed WITHOUT ANY WARRANTY; without even
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// the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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// PURPOSE. See the above copyright notice for more information.
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//============================================================================
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$# This file uses the pyexpander macro processing utility to build the
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$# FunctionInterface facilities that use a variable number of arguments.
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$# Information, documentation, and downloads for pyexpander can be found at:
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$#
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$# http://pyexpander.sourceforge.net/
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$#
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$# To build the source code, execute the following (after installing
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$# pyexpander, of course):
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$#
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$# expander.py VariantDetail.h.in > VariantDetail.h
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$#
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$# Ignore the following comment. It is meant for the generated file.
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// **** DO NOT EDIT THIS FILE!!! ****
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// This file is automatically generated by VariantDetail.h.in
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#if !defined(VTK_M_DEVICE) || !defined(VTK_M_NAMESPACE)
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#error VarianImplDetail.h must be included from VariantImpl.h
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// Some defines to make my IDE happy.
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#define VTK_M_DEVICE
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#define VTK_M_NAMESPACE tmp
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#endif
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#include <vtkm/List.h>
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#include <vtkm/Types.h>
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#include <vtkm/internal/Assume.h>
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#include <vtkmstd/is_trivial.h>
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#include <type_traits>
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$py(max_expanded=8)\
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$# Python commands used in template expansion.
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$py(
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def type_list(num_params):
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if num_params < 0:
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return ''
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result = 'T0'
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for param in range(1, num_params + 1):
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result += ', T%d' % param
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return result
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def typename_list(num_params):
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if num_params < 0:
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return ''
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result = 'typename T0'
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for param in range(1, num_params + 1):
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result += ', typename T%d' % param
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return result
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)\
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$#
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$extend(type_list, typename_list)\
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namespace vtkm
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{
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namespace VTK_M_NAMESPACE
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{
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namespace detail
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{
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// --------------------------------------------------------------------------------
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// Helper classes to determine if all Variant types are trivial.
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template <typename... Ts>
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using AllTriviallyCopyable = vtkm::ListAll<vtkm::List<Ts...>, vtkmstd::is_trivially_copyable>;
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// Single argument version of is_trivially_constructible
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template <typename T>
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using Constructible = vtkmstd::is_trivially_constructible<T>;
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template <typename... Ts>
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using AllTriviallyConstructible = vtkm::ListAll<vtkm::List<Ts...>, Constructible>;
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template <typename... Ts>
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using AllTriviallyDestructible =
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vtkm::ListAll<vtkm::List<Ts...>, vtkmstd::is_trivially_destructible>;
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// clang-format off
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// --------------------------------------------------------------------------------
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// Union type used inside of Variant
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//
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// You may be asking yourself, why not just use an std::aligned_union rather than a real union
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// type? That was our first implementation, but the problem is that the std::aligned_union
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// reference needs to be recast to the actual type. Typically you would do that with
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// reinterpret_cast. However, doing that leads to undefined behavior. The C++ compiler assumes that
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// 2 pointers of different types point to different memory (even if it is clear that they are set
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// to the same address). That means optimizers can remove code because it "knows" that data in one
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// type cannot affect data in another type. (See Shafik Yaghmour's excellent writeup at
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// https://gist.github.com/shafik/848ae25ee209f698763cffee272a58f8 for more details.) To safely
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// change the type of an std::aligned_union, you really have to do an std::memcpy. This is
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// problematic for types that cannot be trivially copied. Another problem is that we found that
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// device compilers do not optimize the memcpy as well as most CPU compilers. Likely, memcpy is
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// used much less frequently on GPU devices.
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//
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// Part of the trickiness of the union implementation is trying to preserve when the type is
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// trivially constructible and copyable. The trick is that if members of the union are not trivial,
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// then the default constructors are deleted. To get around that, a non-default constructor is
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// added, which we can use to construct the union for non-trivial types. Working with types with
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// non-trivial destructors are particularly tricky. Again, if any member of the union has a
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// non-trivial destructor, the destructor is deleted. Unlike a constructor, you cannot just say to
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// use a different destructor. Thus, we have to define our own destructor for the union.
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// Technically, the destructor here does not do anything, but the actual destruction should be
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// handled by the Variant class that contains this VariantUnion. We actually need two separate
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// implementations of our union, one that defines a destructor and one that use the default
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// destructor. If you define your own destructor, you can lose the trivial constructor and trivial
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// copy properties.
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//
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// TD = trivially deconstructible
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template <typename T0, typename... Ts>
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union VariantUnionTD;
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// NTD = non-trivially deconstructible
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template <typename T0, typename... Ts>
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union VariantUnionNTD;
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$for(param_length in range(max_expanded))\
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template <$typename_list(param_length)>
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union VariantUnionTD<$type_list(param_length)>
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{
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$for(param_index in range(param_length + 1))\
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T$(param_index) V$(param_index);
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$endfor\
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VTK_M_DEVICE VariantUnionTD(vtkm::internal::NullType) { }
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VariantUnionTD() = default;
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};
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template <$typename_list(param_length)>
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union VariantUnionNTD<$type_list(param_length)>
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{
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$for(param_index in range(param_length + 1))\
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T$(param_index) V$(param_index);
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$endfor\
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VTK_M_DEVICE VariantUnionNTD(vtkm::internal::NullType) { }
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VariantUnionNTD() = default;
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VTK_M_DEVICE ~VariantUnionNTD() { }
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};
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$endfor\
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template <$typename_list(max_expanded), typename... Ts>
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union VariantUnionTD<$type_list(max_expanded), Ts...>
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{
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$for(param_index in range(max_expanded))\
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T$(param_index) V$(param_index);
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$endfor\
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VariantUnionTD<T$(max_expanded), Ts...> Remaining;
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VTK_M_DEVICE VariantUnionTD(vtkm::internal::NullType) { }
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VariantUnionTD() = default;
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};
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template <$typename_list(max_expanded), typename... Ts>
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union VariantUnionNTD<$type_list(max_expanded), Ts...>
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{
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$for(param_index in range(max_expanded))\
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T$(param_index) V$(param_index);
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$endfor\
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VariantUnionNTD<T$(max_expanded), Ts...> Remaining;
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VTK_M_DEVICE VariantUnionNTD(vtkm::internal::NullType) { }
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VariantUnionNTD() = default;
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VTK_M_DEVICE ~VariantUnionNTD() { }
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};
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//clang-format on
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template <bool TrivialConstructor, typename... Ts>
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struct VariantUnionFinder;
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template <typename... Ts>
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struct VariantUnionFinder<true, Ts...>
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{
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using type = VariantUnionTD<Ts...>;
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};
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template <typename... Ts>
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struct VariantUnionFinder<false, Ts...>
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{
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using type = VariantUnionNTD<Ts...>;
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};
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template <typename... Ts>
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using VariantUnion =
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typename VariantUnionFinder<AllTriviallyDestructible<Ts...>::value, Ts...>::type;
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// --------------------------------------------------------------------------------
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// Methods to get values out of the variant union
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template <vtkm::IdComponent I, typename UnionType>
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struct VariantUnionGetImpl;
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$for(param_index in range(max_expanded))\
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template <typename UnionType>
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struct VariantUnionGetImpl<$(param_index), UnionType>
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{
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using ReturnType = decltype(std::declval<UnionType>().V$(param_index));
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VTK_M_DEVICE static ReturnType& Get(UnionType& storage) noexcept
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{
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return storage.V$(param_index);
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}
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VTK_M_DEVICE static const ReturnType& Get(const UnionType& storage) noexcept
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{
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return storage.V$(param_index);
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}
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};
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$endfor\
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template <vtkm::IdComponent I, typename UnionType>
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struct VariantUnionGetImpl
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{
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VTKM_STATIC_ASSERT(I >= $(max_expanded));
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using RecursiveGet = VariantUnionGetImpl<I - $(max_expanded), decltype(std::declval<UnionType&>().Remaining)>;
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using ReturnType = typename RecursiveGet::ReturnType;
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VTK_M_DEVICE static ReturnType& Get(UnionType& storage) noexcept
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{
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return RecursiveGet::Get(storage.Remaining);
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}
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VTK_M_DEVICE static const ReturnType& Get(const UnionType& storage) noexcept
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{
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return RecursiveGet::Get(storage.Remaining);
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}
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};
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template <vtkm::IdComponent I, typename UnionType>
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VTK_M_DEVICE auto VariantUnionGet(UnionType& storage) noexcept
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-> decltype(VariantUnionGetImpl<I, typename std::decay<UnionType>::type>::Get(storage))&
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{
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return VariantUnionGetImpl<I, typename std::decay<UnionType>::type>::Get(storage);
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}
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// --------------------------------------------------------------------------------
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// Internal implementation of CastAndCall for Variant
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template <std::size_t NumCases>
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struct VariantCases
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{
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template <typename Functor, typename UnionType, typename... Args>
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VTK_M_DEVICE static
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#ifdef VTKM_HIP
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// this is a temporary solution to improve Kokkos/HIP compile times for
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// ConnectivityTracer in Rendering.
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//
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// This function currently gets inlined many times, which dramatically increases
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// both compile time and the size of the resulting code-object
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__attribute__((noinline))
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#else
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inline
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#endif
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auto CastAndCall(
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vtkm::IdComponent index,
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Functor&& f,
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UnionType& storage,
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Args&&... args) noexcept(noexcept(f(storage.V0, args...)))
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-> decltype(f(storage.V0, args...))
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{
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VTKM_ASSERT((index >= 0) && (index < static_cast<vtkm::IdComponent>(NumCases)));
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switch (index)
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{
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$for(param_index in range(max_expanded))\
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case $(param_index):
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// If you get a compile error here, it probably means that you have called
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// Variant::CastAndCall with a functor that does not accept one of the types in the
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// Variant. The functor you provide must be callable with all types in the Variant, not
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// just the one that it currently holds.
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return f(storage.V$(param_index), std::forward<Args>(args)...);
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$endfor\
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default:
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return VariantCases<NumCases - $(max_expanded)>::template CastAndCall(
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index - $(max_expanded), std::forward<Functor>(f), storage.Remaining, std::forward<Args>(args)...);
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}
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}
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};
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template<>
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struct VariantCases<1>
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{
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template <typename Functor, typename UnionType, typename... Args>
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VTK_M_DEVICE static inline auto CastAndCall(
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vtkm::IdComponent index,
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Functor&& f,
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UnionType& storage,
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Args&&... args) noexcept(noexcept(f(storage.V0, args...)))
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-> decltype(f(storage.V0, args...))
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{
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// Assume index is 0. Saves us some conditionals.
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VTKM_ASSERT(index == 0);
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(void)index;
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return f(storage.V0, std::forward<Args>(args)...);
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}
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};
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$for(case_index in range(2, max_expanded + 1))\
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template<>
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struct VariantCases<$(case_index)>
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{
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template <typename Functor, typename UnionType, typename... Args>
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VTK_M_DEVICE static
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#ifdef VTKM_HIP
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// this is a temporary solution to improve Kokkos/HIP compile times for
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// ConnectivityTracer in Rendering.
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//
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// This function currently gets inlined many times, which dramatically increases
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// both compile time and the size of the resulting code-object
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__attribute__((noinline))
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#else
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inline
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#endif
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auto CastAndCall(
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vtkm::IdComponent index,
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Functor&& f,
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UnionType& storage,
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Args&&... args) noexcept(noexcept(f(storage.V0, args...)))
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-> decltype(f(storage.V0, args...))
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{
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// Assume index is 0. Saves us some conditionals.
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VTKM_ASSERT((index >= 0) && (index < $(case_index)));
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switch (index)
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{
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default:
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$for(param_index in range(case_index))\
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case $(param_index):
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// If you get a compile error here, it probably means that you have called
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// Variant::CastAndCall with a functor that does not accept one of the types in the
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// Variant. The functor you provide must be callable with all types in the Variant, not
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// just the one that it currently holds.
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return f(storage.V$(param_index), std::forward<Args>(args)...);
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$endfor\
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}
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}
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};
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$endfor
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template <std::size_t UnionSize, typename Functor, typename UnionType, typename... Args>
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VTK_M_DEVICE inline auto VariantCastAndCallImpl(
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vtkm::IdComponent index,
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Functor&& f,
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UnionType& storage,
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Args&&... args) noexcept(noexcept(f(storage.V0, args...)))
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-> decltype(f(storage.V0, args...))
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{
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return VariantCases<UnionSize>::CastAndCall(
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index, std::forward<Functor>(f), storage, std::forward<Args>(args)...);
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}
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}
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}
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} // vtkm::VTK_M_NAMESPACE::detail
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