src/tint/lang/spirv/writer/raise/var_for_dynamic_index.cc - tint - Git at Google

 // Copyright 2023 The Dawn & Tint Authors
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are met:
 //
 // 1. Redistributions of source code must retain the above copyright notice, this
 //    list of conditions and the following disclaimer.
 //
 // 2. Redistributions in binary form must reproduce the above copyright notice,
 //    this list of conditions and the following disclaimer in the documentation
 //    and/or other materials provided with the distribution.
 //
 // 3. Neither the name of the copyright holder nor the names of its
 //    contributors may be used to endorse or promote products derived from
 //    this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 #include "src/tint/lang/spirv/writer/raise/var_for_dynamic_index.h"

 #include <utility>

 #include "src/tint/lang/core/fluent_types.h"
 #include "src/tint/lang/core/ir/builder.h"
 #include "src/tint/lang/core/ir/module.h"
 #include "src/tint/lang/core/ir/validator.h"
 #include "src/tint/lang/core/type/array.h"
 #include "src/tint/lang/core/type/matrix.h"
 #include "src/tint/lang/core/type/pointer.h"
 #include "src/tint/lang/core/type/vector.h"
 #include "src/tint/utils/containers/hashmap.h"

 using namespace tint::core::number_suffixes;  // NOLINT
 using namespace tint::core::fluent_types;     // NOLINT

 namespace tint::spirv::writer::raise {

 namespace {

 /// PIMPL state for the transform.
 struct State {
     /// The IR module.
     core::ir::Module& ir;

     /// The IR builder.
     core::ir::Builder b{ir};

     /// The type manager.
     core::type::Manager& ty{ir.Types()};

     /// An access that needs replacing.
     struct AccessToReplace {
         /// The access instruction.
         core::ir::Access* access = nullptr;
         /// The index of the first dynamic index.
         size_t first_dynamic_index = 0;
         /// The object type that corresponds to the source of the first dynamic index.
         const core::type::Type* dynamic_index_source_type = nullptr;
         /// If the access indexes a vector, then the type of that vector
         const core::type::Vector* vector_access_type = nullptr;
     };

     /// A partial access chain that uses constant indices to get to an object that will be
     /// dynamically indexed.
     struct PartialAccess {
         /// The base object.
         core::ir::Value* base = nullptr;
         /// The list of constant indices to get from the base to the source object.
         Vector<core::ir::Value*, 4> indices;

         /// @returns the hash code of the PartialAccess
         tint::HashCode HashCode() const { return Hash(base, indices); }

         /// An equality helper for PartialAccess.
         bool operator==(const PartialAccess& other) const {
             return base == other.base && indices == other.indices;
         }
     };

     /// Traversal action for WalkAccessChain.
     enum class Action { kStop, kContinue };

     /// Walk an the access chain @p access, calling @p callback for each intermediate type.
     template <typename CALLBACK>
     void WalkAccessChain(core::ir::Access* access, CALLBACK&& callback) {
         auto indices = access->Indices();
         auto* type = access->Object()->Type();
         for (size_t i = 0; i < indices.Length(); i++) {
             if (callback(i, indices[i], type) == Action::kStop) {
                 break;
             }
             auto* const_idx = indices[i]->As<core::ir::Constant>();
             type = const_idx ? type->Element(const_idx->Value()->ValueAs<u32>())
                              : type->Elements().type;
         }
     }

     /// Check if @p access needs to be replaced.
     /// @returns the access descriptor or std::nullopt
     std::optional<AccessToReplace> ShouldReplace(core::ir::Access* access) {
         if (access->Result(0)->Type()->Is<core::type::Pointer>()) {
             // No need to modify accesses into pointer types.
             return {};
         }

         std::optional<AccessToReplace> result;
         WalkAccessChain(access,
                         [&](size_t i, core::ir::Value* index, const core::type::Type* type) {
                             if (auto* vec = type->As<core::type::Vector>()) {
                                 // If we haven't found a dynamic index before the vector, then the
                                 // transform doesn't need to hoist the access into a var as a vector
                                 // value can be dynamically indexed. If we have found a dynamic
                                 // index before the vector, then make a note that we're indexing a
                                 // vector as we can't obtain a pointer to a vector element, so this
                                 // needs to be handled specially.
                                 if (result) {
                                     result->vector_access_type = vec;
                                 }
                                 return Action::kStop;
                             }

                             // Check if this is the first dynamic index.
                             if (!result && !index->Is<core::ir::Constant>()) {
                                 result = AccessToReplace{access, i, type};
                             }

                             return Action::kContinue;
                         });

         return result;
     }

     /// Process the module.
     void Process() {
         // Find the access instructions that need replacing.
         Vector<AccessToReplace, 4> worklist;
         for (auto* inst : ir.Instructions()) {
             if (auto* access = inst->As<core::ir::Access>()) {
                 if (auto to_replace = ShouldReplace(access)) {
                     worklist.Push(to_replace.value());
                 }
             }
         }

         // Replace each access instruction that we recorded.
         Hashmap<core::ir::Value*, core::ir::Value*, 4> object_to_var;
         Hashmap<PartialAccess, core::ir::Value*, 4> source_object_to_value;
         for (const auto& to_replace : worklist) {
             auto* access = to_replace.access;
             auto* source_object = access->Object();

             // If the access starts with at least one constant index, extract the source of the
             // first dynamic access to avoid copying the whole object.
             if (to_replace.first_dynamic_index > 0) {
                 PartialAccess partial_access = {
                     access->Object(), access->Indices().Truncate(to_replace.first_dynamic_index)};
                 source_object =
                     source_object_to_value.GetOrAdd(partial_access, [&]() -> core::ir::Value* {
                         // If the source is a constant, then the partial access will also produce a
                         // constant. Extract the constant::Value and use that as the new source
                         // object.
                         if (source_object->Is<core::ir::Constant>()) {
                             for (const auto& i : partial_access.indices) {
                                 auto idx =
                                     i->As<core::ir::Constant>()->Value()->ValueAs<uint32_t>();
                                 source_object = b.Constant(
                                     source_object->As<core::ir::Constant>()->Value()->Index(idx));
                             }
                             return source_object;
                         }

                         // Extract a non-constant intermediate source using an access instruction
                         // that we insert immediately after the definition of the root source
                         // object.
                         auto* intermediate_source = b.Access(to_replace.dynamic_index_source_type,
                                                              source_object, partial_access.indices);
                         b.InsertAfter(source_object, [&] { b.Append(intermediate_source); });
                         return intermediate_source->Result(0);
                     });
             }

             // Declare a variable and copy the source object to it.
             auto* var = object_to_var.GetOrAdd(source_object, [&] {
                 // If the source object is a constant we use a module-scope variable, as it could be
                 // indexed by multiple functions. Otherwise, we declare a function-scope variable
                 // immediately after the definition of the source object.
                 core::ir::Var* decl = nullptr;
                 if (source_object->Is<core::ir::Constant>()) {
                     decl = b.Var(ty.ptr(core::AddressSpace::kPrivate, source_object->Type(),
                                         core::Access::kReadWrite));
                     ir.root_block->Append(decl);
                 } else {
                     b.InsertAfter(source_object, [&] {
                         decl = b.Var(ty.ptr(core::AddressSpace::kFunction, source_object->Type(),
                                             core::Access::kReadWrite));

                         // If we ever support value declarations at module-scope, we will need to
                         // modify the partial access logic above since `access` instructions cannot
                         // be used in the root block.
                         TINT_ASSERT(decl->Block() != ir.root_block);
                     });
                 }

                 decl->SetInitializer(source_object);
                 return decl->Result(0);
             });

             // Create a new access instruction using the new variable as the source.
             Vector<core::ir::Value*, 4> indices{
                 access->Indices().Offset(to_replace.first_dynamic_index)};
             const core::type::Type* access_type = access->Result(0)->Type();
             core::ir::Value* vector_index = nullptr;
             if (to_replace.vector_access_type) {
                 // The old access indexed the element of a vector.
                 // Its not valid to obtain the address of an element of a vector, so we need to
                 // access up to the vector, then use LoadVectorElement to load the element. As a
                 // vector element is always a scalar, we know the last index of the access is the
                 // index on the vector. Pop that index to obtain the index to pass to
                 // LoadVectorElement(), and perform the rest of the access chain.
                 access_type = to_replace.vector_access_type;
                 vector_index = indices.Pop();
             }

             auto addrspace = var->Type()->As<core::type::Pointer>()->AddressSpace();
             core::ir::Instruction* new_access =
                 b.Access(ty.ptr(addrspace, access_type, core::Access::kReadWrite), var, indices);
             new_access->InsertBefore(access);

             core::ir::Instruction* load = nullptr;
             if (to_replace.vector_access_type) {
                 load = b.LoadVectorElementWithResult(access->DetachResult(), new_access->Result(0),
                                                      vector_index);
             } else {
                 load = b.LoadWithResult(access->DetachResult(), new_access);
             }
             access->ReplaceWith(load);
             access->Destroy();
         }
     }
 };

 }  // namespace

 Result<SuccessType> VarForDynamicIndex(core::ir::Module& ir) {
     auto result = ValidateAndDumpIfNeeded(ir, "VarForDynamicIndex transform");
     if (result != Success) {
         return result;
     }

     State{ir}.Process();

     return Success;
 }

 }  // namespace tint::spirv::writer::raise
	// Copyright 2023 The Dawn & Tint Authors
	//
	// Redistribution and use in source and binary forms, with or without
	// modification, are permitted provided that the following conditions are met:
	//
	// 1. Redistributions of source code must retain the above copyright notice, this
	// list of conditions and the following disclaimer.
	//
	// 2. Redistributions in binary form must reproduce the above copyright notice,
	// this list of conditions and the following disclaimer in the documentation
	// and/or other materials provided with the distribution.
	//
	// 3. Neither the name of the copyright holder nor the names of its
	// contributors may be used to endorse or promote products derived from
	// this software without specific prior written permission.
	//
	// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
	// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
	// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
	// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
	// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
	// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
	// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
	// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	#include "src/tint/lang/spirv/writer/raise/var_for_dynamic_index.h"

	#include <utility>

	#include "src/tint/lang/core/fluent_types.h"
	#include "src/tint/lang/core/ir/builder.h"
	#include "src/tint/lang/core/ir/module.h"
	#include "src/tint/lang/core/ir/validator.h"
	#include "src/tint/lang/core/type/array.h"
	#include "src/tint/lang/core/type/matrix.h"
	#include "src/tint/lang/core/type/pointer.h"
	#include "src/tint/lang/core/type/vector.h"
	#include "src/tint/utils/containers/hashmap.h"

	using namespace tint::core::number_suffixes; // NOLINT
	using namespace tint::core::fluent_types; // NOLINT

	namespace tint::spirv::writer::raise {

	namespace {

	/// PIMPL state for the transform.
	struct State {
	/// The IR module.
	core::ir::Module& ir;

	/// The IR builder.
	core::ir::Builder b{ir};

	/// The type manager.
	core::type::Manager& ty{ir.Types()};

	/// An access that needs replacing.
	struct AccessToReplace {
	/// The access instruction.
	core::ir::Access* access = nullptr;
	/// The index of the first dynamic index.
	size_t first_dynamic_index = 0;
	/// The object type that corresponds to the source of the first dynamic index.
	const core::type::Type* dynamic_index_source_type = nullptr;
	/// If the access indexes a vector, then the type of that vector
	const core::type::Vector* vector_access_type = nullptr;
	};

	/// A partial access chain that uses constant indices to get to an object that will be
	/// dynamically indexed.
	struct PartialAccess {
	/// The base object.
	core::ir::Value* base = nullptr;
	/// The list of constant indices to get from the base to the source object.
	Vector<core::ir::Value*, 4> indices;

	/// @returns the hash code of the PartialAccess
	tint::HashCode HashCode() const { return Hash(base, indices); }

	/// An equality helper for PartialAccess.
	bool operator==(const PartialAccess& other) const {
	return base == other.base && indices == other.indices;
	}
	};

	/// Traversal action for WalkAccessChain.
	enum class Action { kStop, kContinue };

	/// Walk an the access chain @p access, calling @p callback for each intermediate type.
	template <typename CALLBACK>
	void WalkAccessChain(core::ir::Access* access, CALLBACK&& callback) {
	auto indices = access->Indices();
	auto* type = access->Object()->Type();
	for (size_t i = 0; i < indices.Length(); i++) {
	if (callback(i, indices[i], type) == Action::kStop) {
	break;
	}
	auto* const_idx = indices[i]->As<core::ir::Constant>();
	type = const_idx ? type->Element(const_idx->Value()->ValueAs<u32>())
	: type->Elements().type;
	}
	}

	/// Check if @p access needs to be replaced.
	/// @returns the access descriptor or std::nullopt
	std::optional<AccessToReplace> ShouldReplace(core::ir::Access* access) {
	if (access->Result(0)->Type()->Is<core::type::Pointer>()) {
	// No need to modify accesses into pointer types.
	return {};
	}

	std::optional<AccessToReplace> result;
	WalkAccessChain(access,
	[&](size_t i, core::ir::Value* index, const core::type::Type* type) {
	if (auto* vec = type->As<core::type::Vector>()) {
	// If we haven't found a dynamic index before the vector, then the
	// transform doesn't need to hoist the access into a var as a vector
	// value can be dynamically indexed. If we have found a dynamic
	// index before the vector, then make a note that we're indexing a
	// vector as we can't obtain a pointer to a vector element, so this
	// needs to be handled specially.
	if (result) {
	result->vector_access_type = vec;
	}
	return Action::kStop;
	}

	// Check if this is the first dynamic index.
	if (!result && !index->Is<core::ir::Constant>()) {
	result = AccessToReplace{access, i, type};
	}

	return Action::kContinue;
	});

	return result;
	}

	/// Process the module.
	void Process() {
	// Find the access instructions that need replacing.
	Vector<AccessToReplace, 4> worklist;
	for (auto* inst : ir.Instructions()) {
	if (auto* access = inst->As<core::ir::Access>()) {
	if (auto to_replace = ShouldReplace(access)) {
	worklist.Push(to_replace.value());
	}
	}
	}

	// Replace each access instruction that we recorded.
	Hashmap<core::ir::Value, core::ir::Value, 4> object_to_var;
	Hashmap<PartialAccess, core::ir::Value*, 4> source_object_to_value;
	for (const auto& to_replace : worklist) {
	auto* access = to_replace.access;
	auto* source_object = access->Object();

	// If the access starts with at least one constant index, extract the source of the
	// first dynamic access to avoid copying the whole object.
	if (to_replace.first_dynamic_index > 0) {
	PartialAccess partial_access = {
	access->Object(), access->Indices().Truncate(to_replace.first_dynamic_index)};
	source_object =
	source_object_to_value.GetOrAdd(partial_access, [&]() -> core::ir::Value* {
	// If the source is a constant, then the partial access will also produce a
	// constant. Extract the constant::Value and use that as the new source
	// object.
	if (source_object->Is<core::ir::Constant>()) {
	for (const auto& i : partial_access.indices) {
	auto idx =
	i->As<core::ir::Constant>()->Value()->ValueAs<uint32_t>();
	source_object = b.Constant(
	source_object->As<core::ir::Constant>()->Value()->Index(idx));
	}
	return source_object;
	}

	// Extract a non-constant intermediate source using an access instruction
	// that we insert immediately after the definition of the root source
	// object.
	auto* intermediate_source = b.Access(to_replace.dynamic_index_source_type,
	source_object, partial_access.indices);
	b.InsertAfter(source_object, [&] { b.Append(intermediate_source); });
	return intermediate_source->Result(0);
	});
	}

	// Declare a variable and copy the source object to it.
	auto* var = object_to_var.GetOrAdd(source_object, [&] {
	// If the source object is a constant we use a module-scope variable, as it could be
	// indexed by multiple functions. Otherwise, we declare a function-scope variable
	// immediately after the definition of the source object.
	core::ir::Var* decl = nullptr;
	if (source_object->Is<core::ir::Constant>()) {
	decl = b.Var(ty.ptr(core::AddressSpace::kPrivate, source_object->Type(),
	core::Access::kReadWrite));
	ir.root_block->Append(decl);
	} else {
	b.InsertAfter(source_object, [&] {
	decl = b.Var(ty.ptr(core::AddressSpace::kFunction, source_object->Type(),
	core::Access::kReadWrite));

	// If we ever support value declarations at module-scope, we will need to
	// modify the partial access logic above since `access` instructions cannot
	// be used in the root block.
	TINT_ASSERT(decl->Block() != ir.root_block);
	});
	}

	decl->SetInitializer(source_object);
	return decl->Result(0);
	});

	// Create a new access instruction using the new variable as the source.
	Vector<core::ir::Value*, 4> indices{
	access->Indices().Offset(to_replace.first_dynamic_index)};
	const core::type::Type* access_type = access->Result(0)->Type();
	core::ir::Value* vector_index = nullptr;
	if (to_replace.vector_access_type) {
	// The old access indexed the element of a vector.
	// Its not valid to obtain the address of an element of a vector, so we need to
	// access up to the vector, then use LoadVectorElement to load the element. As a
	// vector element is always a scalar, we know the last index of the access is the
	// index on the vector. Pop that index to obtain the index to pass to
	// LoadVectorElement(), and perform the rest of the access chain.
	access_type = to_replace.vector_access_type;
	vector_index = indices.Pop();
	}

	auto addrspace = var->Type()->As<core::type::Pointer>()->AddressSpace();
	core::ir::Instruction* new_access =
	b.Access(ty.ptr(addrspace, access_type, core::Access::kReadWrite), var, indices);
	new_access->InsertBefore(access);

	core::ir::Instruction* load = nullptr;
	if (to_replace.vector_access_type) {
	load = b.LoadVectorElementWithResult(access->DetachResult(), new_access->Result(0),
	vector_index);
	} else {
	load = b.LoadWithResult(access->DetachResult(), new_access);
	}
	access->ReplaceWith(load);
	access->Destroy();
	}
	}
	};

	} // namespace

	Result<SuccessType> VarForDynamicIndex(core::ir::Module& ir) {
	auto result = ValidateAndDumpIfNeeded(ir, "VarForDynamicIndex transform");
	if (result != Success) {
	return result;
	}

	State{ir}.Process();

	return Success;
	}

	} // namespace tint::spirv::writer::raise