src/tint/lang/glsl/writer/ast_raise/combine_samplers.cc - dawn - Git at Google

 // Copyright 2022 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/glsl/writer/ast_raise/combine_samplers.h"

 #include <string>
 #include <unordered_map>
 #include <utility>
 #include <vector>

 #include "src/tint/lang/wgsl/program/clone_context.h"
 #include "src/tint/lang/wgsl/program/program_builder.h"
 #include "src/tint/lang/wgsl/resolver/resolve.h"
 #include "src/tint/lang/wgsl/sem/function.h"
 #include "src/tint/lang/wgsl/sem/statement.h"

 #include "src/tint/utils/containers/map.h"

 TINT_INSTANTIATE_TYPEINFO(tint::glsl::writer::CombineSamplers);
 TINT_INSTANTIATE_TYPEINFO(tint::glsl::writer::CombineSamplers::BindingInfo);

 namespace {

 bool IsGlobal(const tint::sem::VariablePair& pair) {
     return (!pair.first || tint::Is<tint::sem::GlobalVariable>(pair.first)) &&
            (!pair.second || tint::Is<tint::sem::GlobalVariable>(pair.second));
 }

 }  // namespace

 namespace tint::glsl::writer {

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

 CombineSamplers::BindingInfo::BindingInfo(const BindingMap& map, const BindingPoint& placeholder)
     : binding_map(map), placeholder_binding_point(placeholder) {}
 CombineSamplers::BindingInfo::BindingInfo(const BindingInfo& other) = default;
 CombineSamplers::BindingInfo::~BindingInfo() = default;

 /// PIMPL state for the transform
 struct CombineSamplers::State {
     /// The source program
     const Program& src;
     /// The target program builder
     ProgramBuilder b;
     /// The clone context
     program::CloneContext ctx = {&b, &src, /* auto_clone_symbols */ true};

     /// The binding info
     const BindingInfo* binding_info;

     /// Map from a texture/sampler pair to the corresponding combined sampler
     /// variable
     using CombinedTextureSamplerMap = std::unordered_map<sem::VariablePair, const ast::Variable*>;

     /// A map of all global texture/sampler variable pairs to the global
     /// combined sampler variable that will replace it.
     CombinedTextureSamplerMap global_combined_texture_samplers_;

     /// A map of all texture/sampler variable pairs that contain a function
     /// parameter to the combined sampler function paramter that will replace it.
     std::unordered_map<const sem::Function*, CombinedTextureSamplerMap>
         function_combined_texture_samplers_;

     /// Placeholder global samplers used when a function contains texture-only
     /// references (one comparison sampler, one regular). These are also used as
     /// temporary sampler parameters to the texture builtins to satisfy the WGSL
     /// resolver, but are then ignored and removed by the GLSL writer.
     const ast::Variable* placeholder_samplers_[2] = {};

     /// Group and binding attributes used by all combined sampler globals.
     /// Group 0 and binding 0 are used, with collisions disabled.
     /// @returns the newly-created attribute list
     auto Attributes() const {
         Vector<const ast::Attribute*, 3> attributes{ctx.dst->Group(0_a), ctx.dst->Binding(0_a)};
         attributes.Push(ctx.dst->Disable(ast::DisabledValidation::kBindingPointCollision));
         return attributes;
     }

     /// Constructor
     /// @param program the source program
     /// @param info the binding map information
     State(const Program& program, const BindingInfo* info) : src(program), binding_info(info) {}

     /// Creates a combined sampler global variables.
     /// (Note this is actually a Texture node at the AST level, but it will be
     /// written as the corresponding sampler (eg., sampler2D) on GLSL output.)
     /// @param texture_var the texture (global) variable
     /// @param sampler_var the sampler (global) variable
     /// @param name the default name to use (may be overridden by map lookup)
     /// @returns the newly-created global variable
     const ast::Variable* CreateCombinedGlobal(const sem::Variable* texture_var,
                                               const sem::Variable* sampler_var,
                                               std::string name) {
         SamplerTexturePair bp_pair;
         bp_pair.texture_binding_point =
             texture_var ? *texture_var->As<sem::GlobalVariable>()->Attributes().binding_point
                         : binding_info->placeholder_binding_point;
         bp_pair.sampler_binding_point =
             sampler_var ? *sampler_var->As<sem::GlobalVariable>()->Attributes().binding_point
                         : binding_info->placeholder_binding_point;
         auto it = binding_info->binding_map.find(bp_pair);
         if (it != binding_info->binding_map.end()) {
             name = it->second;
         }
         ast::Type type = CreateCombinedASTTypeFor(texture_var, sampler_var);
         Symbol symbol = ctx.dst->Symbols().New(name);
         return ctx.dst->GlobalVar(symbol, type, Attributes());
     }

     /// Creates placeholder global sampler variables.
     /// @param kind the sampler kind to create for
     /// @returns the newly-created global variable
     const ast::Variable* CreatePlaceholder(core::type::SamplerKind kind) {
         ast::Type type = ctx.dst->ty.sampler(kind);
         const char* name = kind == core::type::SamplerKind::kComparisonSampler
                                ? "placeholder_comparison_sampler"
                                : "placeholder_sampler";
         Symbol symbol = ctx.dst->Symbols().New(name);
         return ctx.dst->GlobalVar(symbol, type, Attributes());
     }

     /// Creates Identifier for a given texture and sampler variable pair.
     /// Depth textures with no samplers are turned into the corresponding
     /// f32 texture (e.g., texture_depth_2d -> texture_2d<f32>).
     /// Either texture or sampler could be nullptr, but cannot be nullptr at the same time.
     /// The texture can only be nullptr, when the sampler is a dangling function parameter.
     /// @param texture the texture variable of interest
     /// @param sampler the texture variable of interest
     /// @returns the newly-created type
     ast::Type CreateCombinedASTTypeFor(const sem::Variable* texture, const sem::Variable* sampler) {
         if (texture) {
             const core::type::Type* texture_type = texture->Type()->UnwrapRef();
             const core::type::DepthTexture* depth = texture_type->As<core::type::DepthTexture>();
             if (depth && !sampler) {
                 return ctx.dst->ty.sampled_texture(depth->dim(), ctx.dst->ty.f32());
             } else {
                 return CreateASTTypeFor(ctx, texture_type);
             }
         } else {
             TINT_ASSERT(sampler != nullptr);
             const core::type::Type* sampler_type = sampler->Type()->UnwrapRef();
             return CreateASTTypeFor(ctx, sampler_type);
         }
     }

     /// Insert a new texture/sampler pair into the combined samplers maps (global or local, as
     /// appropriate). If local, also add a function parameter to "params".
     /// @param pair the texture/sampler pair to insert
     /// @param fn the function scope in which to insert (if local)
     /// @param params the calling function's parameter list to modify (if local)
     void InsertPair(sem::VariablePair pair,
                     const sem::Function* fn,
                     tint::Vector<const ast::Parameter*, 8>* params) {
         const sem::Variable* texture_var = pair.first;
         const sem::Variable* sampler_var = pair.second;
         std::string name = "";
         if (texture_var) {
             name = texture_var->Declaration()->name->symbol.Name();
         }
         if (sampler_var) {
             if (!name.empty()) {
                 name += "_";
             }
             name += sampler_var->Declaration()->name->symbol.Name();
         }
         if (IsGlobal(pair)) {
             // Both texture and sampler are global; add a new global variable
             // to represent the combined sampler (if not already created).
             GetOrCreate(global_combined_texture_samplers_, pair,
                         [&] { return CreateCombinedGlobal(texture_var, sampler_var, name); });
         } else {
             // Either texture or sampler (or both) is a function parameter;
             // add a new function parameter to represent the combined sampler.
             ast::Type type = CreateCombinedASTTypeFor(texture_var, sampler_var);
             auto* var = ctx.dst->Param(ctx.dst->Symbols().New(name), type);
             params->Push(var);
             function_combined_texture_samplers_[fn][pair] = var;
         }
     }

     /// For a given texture, find any texture/sampler pair with a non-null sampler in the given
     /// function scope.
     /// @param texture_var the texture variable of interest
     /// @param fn the function scope in which to search
     /// @returns the full pair, if found
     const sem::VariablePair* FindFullTextureSamplerPair(const sem::Variable* texture_var,
                                                         const sem::Function* fn) {
         for (auto pairIter = fn->TextureSamplerPairs().begin();
              pairIter != fn->TextureSamplerPairs().end(); pairIter++) {
             if (pairIter->first == texture_var && pairIter->second) {
                 return pairIter;
             }
         }
         return nullptr;
     }

     /// Runs the transform
     /// @returns the new program or SkipTransform if the transform is not required
     ApplyResult Run() {
         auto& sem = ctx.src->Sem();

         // Remove all texture and sampler global variables. These will be replaced
         // by combined samplers.
         for (auto* global : ctx.src->AST().GlobalVariables()) {
             auto* global_sem = sem.Get(global)->As<sem::GlobalVariable>();
             auto* type = ctx.src->TypeOf(global->type);
             if (tint::IsAnyOf<core::type::Texture, core::type::Sampler>(type) &&
                 !type->Is<core::type::StorageTexture>()) {
                 ctx.Remove(ctx.src->AST().GlobalDeclarations(), global);
             } else if (auto binding_point = global_sem->Attributes().binding_point) {
                 if (binding_point->group == 0 && binding_point->binding == 0) {
                     auto* attribute =
                         ctx.dst->Disable(ast::DisabledValidation::kBindingPointCollision);
                     ctx.InsertFront(global->attributes, attribute);
                 }
             }
         }

         // Rewrite all function signatures to use combined samplers, and remove
         // separate textures & samplers. Create new combined globals where found.
         ctx.ReplaceAll([&](const ast::Function* ast_fn) -> const ast::Function* {
             if (auto* fn = sem.Get(ast_fn)) {
                 auto pairs = fn->TextureSamplerPairs();
                 if (pairs.IsEmpty()) {
                     return nullptr;
                 }
                 Vector<const ast::Parameter*, 8> params;
                 for (auto pair : fn->TextureSamplerPairs()) {
                     if (!pair.second) {
                         continue;
                     }
                     InsertPair(pair, fn, &params);
                 }
                 for (auto pair : fn->TextureSamplerPairs()) {
                     if (pair.second) {
                         continue;
                     }
                     // Look for another pair with a non-null sampler.
                     // NOTE: this is O(N^2) in the number of pairs, since
                     // FindFullTextureSamplerPair() also loops over all pairs. If this proves
                     // problematic, it could be optimized.
                     if (const sem::VariablePair* fullPair =
                             FindFullTextureSamplerPair(pair.first, fn)) {
                         if (IsGlobal(pair)) {
                             global_combined_texture_samplers_[pair] =
                                 global_combined_texture_samplers_[*fullPair];
                         } else {
                             auto* var = function_combined_texture_samplers_[fn][*fullPair];
                             function_combined_texture_samplers_[fn][pair] = var;
                         }
                     } else {
                         InsertPair(pair, fn, &params);
                     }
                 }
                 // Filter out separate textures and samplers from the original
                 // function signature.
                 for (auto* param : fn->Parameters()) {
                     if (!param->Type()->IsAnyOf<core::type::Texture, core::type::Sampler>()) {
                         params.Push(ctx.Clone(param->Declaration()));
                     }
                 }
                 // Create a new function signature that differs only in the parameter
                 // list.
                 auto name = ctx.Clone(ast_fn->name);
                 auto return_type = ctx.Clone(ast_fn->return_type);
                 auto* body = ctx.Clone(ast_fn->body);
                 auto attributes = ctx.Clone(ast_fn->attributes);
                 auto return_type_attributes = ctx.Clone(ast_fn->return_type_attributes);
                 return ctx.dst->create<ast::Function>(name, params, return_type, body,
                                                       std::move(attributes),
                                                       std::move(return_type_attributes));
             }
             return nullptr;
         });

         // Replace all function call expressions containing texture or
         // sampler parameters to use the current function's combined samplers or
         // the combined global samplers, as appropriate.
         ctx.ReplaceAll([&](const ast::CallExpression* expr) -> const ast::Expression* {
             if (auto* call = sem.Get(expr)->UnwrapMaterialize()->As<sem::Call>()) {
                 Vector<const ast::Expression*, 8> args;
                 // Replace all texture builtin calls.
                 if (auto* builtin = call->Target()->As<sem::BuiltinFn>()) {
                     const auto& signature = builtin->Signature();
                     auto sampler_index = signature.IndexOf(core::ParameterUsage::kSampler);
                     auto texture_index = signature.IndexOf(core::ParameterUsage::kTexture);
                     if (texture_index == -1) {
                         return nullptr;
                     }
                     const sem::ValueExpression* texture =
                         call->Arguments()[static_cast<size_t>(texture_index)];
                     // We don't want to combine storage textures with anything, since
                     // they never have associated samplers in GLSL.
                     if (texture->Type()->UnwrapRef()->Is<core::type::StorageTexture>()) {
                         return nullptr;
                     }
                     const sem::ValueExpression* sampler =
                         sampler_index != -1 ? call->Arguments()[static_cast<size_t>(sampler_index)]
                                             : nullptr;
                     auto* texture_var = texture->UnwrapLoad()->As<sem::VariableUser>()->Variable();
                     auto* sampler_var =
                         sampler ? sampler->UnwrapLoad()->As<sem::VariableUser>()->Variable()
                                 : nullptr;
                     sem::VariablePair new_pair(texture_var, sampler_var);
                     for (auto* arg : expr->args) {
                         auto* type = ctx.src->TypeOf(arg)->UnwrapRef();
                         if (type->Is<core::type::Texture>()) {
                             const ast::Variable* var =
                                 IsGlobal(new_pair)
                                     ? global_combined_texture_samplers_[new_pair]
                                     : function_combined_texture_samplers_[call->Stmt()->Function()]
                                                                          [new_pair];
                             args.Push(ctx.dst->Expr(var->name->symbol));
                         } else if (auto* sampler_type = type->As<core::type::Sampler>()) {
                             core::type::SamplerKind kind = sampler_type->kind();
                             int index = (kind == core::type::SamplerKind::kSampler) ? 0 : 1;
                             const ast::Variable*& p = placeholder_samplers_[index];
                             if (!p) {
                                 p = CreatePlaceholder(kind);
                             }
                             args.Push(ctx.dst->Expr(p->name->symbol));
                         } else {
                             args.Push(ctx.Clone(arg));
                         }
                     }
                     const ast::Expression* value = ctx.dst->Call(ctx.Clone(expr->target), args);
                     if (builtin->Fn() == wgsl::BuiltinFn::kTextureLoad &&
                         texture_var->Type()->UnwrapRef()->Is<core::type::DepthTexture>() &&
                         !call->Stmt()->Declaration()->Is<ast::CallStatement>()) {
                         value = ctx.dst->MemberAccessor(value, "x");
                     }
                     return value;
                 }
                 // Replace all function calls.
                 if (auto* callee = call->Target()->As<sem::Function>()) {
                     for (auto pair : callee->TextureSamplerPairs()) {
                         // Global pairs used by the callee do not require a function
                         // parameter at the call site.
                         if (IsGlobal(pair)) {
                             continue;
                         }
                         // Texture-only pairs do not require a function parameter if they've been
                         // replaced by a real pair.
                         if (!pair.second && FindFullTextureSamplerPair(pair.first, callee)) {
                             continue;
                         }

                         const sem::Variable* texture_var = pair.first;
                         const sem::Variable* sampler_var = pair.second;
                         if (auto* param = texture_var->As<sem::Parameter>()) {
                             const sem::ValueExpression* texture = call->Arguments()[param->Index()];
                             texture_var =
                                 texture->UnwrapLoad()->As<sem::VariableUser>()->Variable();
                         }
                         if (sampler_var) {
                             if (auto* param = sampler_var->As<sem::Parameter>()) {
                                 const sem::ValueExpression* sampler =
                                     call->Arguments()[param->Index()];
                                 sampler_var =
                                     sampler->UnwrapLoad()->As<sem::VariableUser>()->Variable();
                             }
                         }
                         sem::VariablePair new_pair(texture_var, sampler_var);
                         // If both texture and sampler are (now) global, pass that
                         // global variable to the callee. Otherwise use the caller's
                         // function parameter for this pair.
                         const ast::Variable* var =
                             IsGlobal(new_pair)
                                 ? global_combined_texture_samplers_[new_pair]
                                 : function_combined_texture_samplers_[call->Stmt()->Function()]
                                                                      [new_pair];
                         auto* arg = ctx.dst->Expr(var->name->symbol);
                         args.Push(arg);
                     }
                     // Append all of the remaining non-texture and non-sampler
                     // parameters.
                     for (auto* arg : expr->args) {
                         if (!ctx.src->TypeOf(arg)
                                  ->UnwrapRef()
                                  ->IsAnyOf<core::type::Texture, core::type::Sampler>()) {
                             args.Push(ctx.Clone(arg));
                         }
                     }
                     return ctx.dst->Call(ctx.Clone(expr->target), args);
                 }
             }
             return nullptr;
         });

         ctx.Clone();
         return resolver::Resolve(b);
     }
 };

 CombineSamplers::CombineSamplers() = default;

 CombineSamplers::~CombineSamplers() = default;

 ast::transform::Transform::ApplyResult CombineSamplers::Apply(const Program& src,
                                                               const ast::transform::DataMap& inputs,
                                                               ast::transform::DataMap&) const {
     auto* binding_info = inputs.Get<BindingInfo>();
     if (!binding_info) {
         ProgramBuilder b;
         b.Diagnostics().add_error(diag::System::Transform,
                                   "missing transform data for " + std::string(TypeInfo().name));
         return resolver::Resolve(b);
     }

     return State(src, binding_info).Run();
 }

 }  // namespace tint::glsl::writer
	// Copyright 2022 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/glsl/writer/ast_raise/combine_samplers.h"

	#include <string>
	#include <unordered_map>
	#include <utility>
	#include <vector>

	#include "src/tint/lang/wgsl/program/clone_context.h"
	#include "src/tint/lang/wgsl/program/program_builder.h"
	#include "src/tint/lang/wgsl/resolver/resolve.h"
	#include "src/tint/lang/wgsl/sem/function.h"
	#include "src/tint/lang/wgsl/sem/statement.h"

	#include "src/tint/utils/containers/map.h"

	TINT_INSTANTIATE_TYPEINFO(tint::glsl::writer::CombineSamplers);
	TINT_INSTANTIATE_TYPEINFO(tint::glsl::writer::CombineSamplers::BindingInfo);

	namespace {

	bool IsGlobal(const tint::sem::VariablePair& pair) {
	return (!pair.first \|\| tint::Is<tint::sem::GlobalVariable>(pair.first)) &&
	(!pair.second \|\| tint::Is<tint::sem::GlobalVariable>(pair.second));
	}

	} // namespace

	namespace tint::glsl::writer {

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

	CombineSamplers::BindingInfo::BindingInfo(const BindingMap& map, const BindingPoint& placeholder)
	: binding_map(map), placeholder_binding_point(placeholder) {}
	CombineSamplers::BindingInfo::BindingInfo(const BindingInfo& other) = default;
	CombineSamplers::BindingInfo::~BindingInfo() = default;

	/// PIMPL state for the transform
	struct CombineSamplers::State {
	/// The source program
	const Program& src;
	/// The target program builder
	ProgramBuilder b;
	/// The clone context
	program::CloneContext ctx = {&b, &src, /* auto_clone_symbols */ true};

	/// The binding info
	const BindingInfo* binding_info;

	/// Map from a texture/sampler pair to the corresponding combined sampler
	/// variable
	using CombinedTextureSamplerMap = std::unordered_map<sem::VariablePair, const ast::Variable*>;

	/// A map of all global texture/sampler variable pairs to the global
	/// combined sampler variable that will replace it.
	CombinedTextureSamplerMap global_combined_texture_samplers_;

	/// A map of all texture/sampler variable pairs that contain a function
	/// parameter to the combined sampler function paramter that will replace it.
	std::unordered_map<const sem::Function*, CombinedTextureSamplerMap>
	function_combined_texture_samplers_;

	/// Placeholder global samplers used when a function contains texture-only
	/// references (one comparison sampler, one regular). These are also used as
	/// temporary sampler parameters to the texture builtins to satisfy the WGSL
	/// resolver, but are then ignored and removed by the GLSL writer.
	const ast::Variable* placeholder_samplers_[2] = {};

	/// Group and binding attributes used by all combined sampler globals.
	/// Group 0 and binding 0 are used, with collisions disabled.
	/// @returns the newly-created attribute list
	auto Attributes() const {
	Vector<const ast::Attribute*, 3> attributes{ctx.dst->Group(0_a), ctx.dst->Binding(0_a)};
	attributes.Push(ctx.dst->Disable(ast::DisabledValidation::kBindingPointCollision));
	return attributes;
	}

	/// Constructor
	/// @param program the source program
	/// @param info the binding map information
	State(const Program& program, const BindingInfo* info) : src(program), binding_info(info) {}

	/// Creates a combined sampler global variables.
	/// (Note this is actually a Texture node at the AST level, but it will be
	/// written as the corresponding sampler (eg., sampler2D) on GLSL output.)
	/// @param texture_var the texture (global) variable
	/// @param sampler_var the sampler (global) variable
	/// @param name the default name to use (may be overridden by map lookup)
	/// @returns the newly-created global variable
	const ast::Variable* CreateCombinedGlobal(const sem::Variable* texture_var,
	const sem::Variable* sampler_var,
	std::string name) {
	SamplerTexturePair bp_pair;
	bp_pair.texture_binding_point =
	texture_var ? *texture_var->As<sem::GlobalVariable>()->Attributes().binding_point
	: binding_info->placeholder_binding_point;
	bp_pair.sampler_binding_point =
	sampler_var ? *sampler_var->As<sem::GlobalVariable>()->Attributes().binding_point
	: binding_info->placeholder_binding_point;
	auto it = binding_info->binding_map.find(bp_pair);
	if (it != binding_info->binding_map.end()) {
	name = it->second;
	}
	ast::Type type = CreateCombinedASTTypeFor(texture_var, sampler_var);
	Symbol symbol = ctx.dst->Symbols().New(name);
	return ctx.dst->GlobalVar(symbol, type, Attributes());
	}

	/// Creates placeholder global sampler variables.
	/// @param kind the sampler kind to create for
	/// @returns the newly-created global variable
	const ast::Variable* CreatePlaceholder(core::type::SamplerKind kind) {
	ast::Type type = ctx.dst->ty.sampler(kind);
	const char* name = kind == core::type::SamplerKind::kComparisonSampler
	? "placeholder_comparison_sampler"
	: "placeholder_sampler";
	Symbol symbol = ctx.dst->Symbols().New(name);
	return ctx.dst->GlobalVar(symbol, type, Attributes());
	}

	/// Creates Identifier for a given texture and sampler variable pair.
	/// Depth textures with no samplers are turned into the corresponding
	/// f32 texture (e.g., texture_depth_2d -> texture_2d<f32>).
	/// Either texture or sampler could be nullptr, but cannot be nullptr at the same time.
	/// The texture can only be nullptr, when the sampler is a dangling function parameter.
	/// @param texture the texture variable of interest
	/// @param sampler the texture variable of interest
	/// @returns the newly-created type
	ast::Type CreateCombinedASTTypeFor(const sem::Variable* texture, const sem::Variable* sampler) {
	if (texture) {
	const core::type::Type* texture_type = texture->Type()->UnwrapRef();
	const core::type::DepthTexture* depth = texture_type->As<core::type::DepthTexture>();
	if (depth && !sampler) {
	return ctx.dst->ty.sampled_texture(depth->dim(), ctx.dst->ty.f32());
	} else {
	return CreateASTTypeFor(ctx, texture_type);
	}
	} else {
	TINT_ASSERT(sampler != nullptr);
	const core::type::Type* sampler_type = sampler->Type()->UnwrapRef();
	return CreateASTTypeFor(ctx, sampler_type);
	}
	}

	/// Insert a new texture/sampler pair into the combined samplers maps (global or local, as
	/// appropriate). If local, also add a function parameter to "params".
	/// @param pair the texture/sampler pair to insert
	/// @param fn the function scope in which to insert (if local)
	/// @param params the calling function's parameter list to modify (if local)
	void InsertPair(sem::VariablePair pair,
	const sem::Function* fn,
	tint::Vector<const ast::Parameter, 8> params) {
	const sem::Variable* texture_var = pair.first;
	const sem::Variable* sampler_var = pair.second;
	std::string name = "";
	if (texture_var) {
	name = texture_var->Declaration()->name->symbol.Name();
	}
	if (sampler_var) {
	if (!name.empty()) {
	name += "_";
	}
	name += sampler_var->Declaration()->name->symbol.Name();
	}
	if (IsGlobal(pair)) {
	// Both texture and sampler are global; add a new global variable
	// to represent the combined sampler (if not already created).
	GetOrCreate(global_combined_texture_samplers_, pair,
	[&] { return CreateCombinedGlobal(texture_var, sampler_var, name); });
	} else {
	// Either texture or sampler (or both) is a function parameter;
	// add a new function parameter to represent the combined sampler.
	ast::Type type = CreateCombinedASTTypeFor(texture_var, sampler_var);
	auto* var = ctx.dst->Param(ctx.dst->Symbols().New(name), type);
	params->Push(var);
	function_combined_texture_samplers_[fn][pair] = var;
	}
	}

	/// For a given texture, find any texture/sampler pair with a non-null sampler in the given
	/// function scope.
	/// @param texture_var the texture variable of interest
	/// @param fn the function scope in which to search
	/// @returns the full pair, if found
	const sem::VariablePair* FindFullTextureSamplerPair(const sem::Variable* texture_var,
	const sem::Function* fn) {
	for (auto pairIter = fn->TextureSamplerPairs().begin();
	pairIter != fn->TextureSamplerPairs().end(); pairIter++) {
	if (pairIter->first == texture_var && pairIter->second) {
	return pairIter;
	}
	}
	return nullptr;
	}

	/// Runs the transform
	/// @returns the new program or SkipTransform if the transform is not required
	ApplyResult Run() {
	auto& sem = ctx.src->Sem();

	// Remove all texture and sampler global variables. These will be replaced
	// by combined samplers.
	for (auto* global : ctx.src->AST().GlobalVariables()) {
	auto* global_sem = sem.Get(global)->As<sem::GlobalVariable>();
	auto* type = ctx.src->TypeOf(global->type);
	if (tint::IsAnyOf<core::type::Texture, core::type::Sampler>(type) &&
	!type->Is<core::type::StorageTexture>()) {
	ctx.Remove(ctx.src->AST().GlobalDeclarations(), global);
	} else if (auto binding_point = global_sem->Attributes().binding_point) {
	if (binding_point->group == 0 && binding_point->binding == 0) {
	auto* attribute =
	ctx.dst->Disable(ast::DisabledValidation::kBindingPointCollision);
	ctx.InsertFront(global->attributes, attribute);
	}
	}
	}

	// Rewrite all function signatures to use combined samplers, and remove
	// separate textures & samplers. Create new combined globals where found.
	ctx.ReplaceAll([&](const ast::Function* ast_fn) -> const ast::Function* {
	if (auto* fn = sem.Get(ast_fn)) {
	auto pairs = fn->TextureSamplerPairs();
	if (pairs.IsEmpty()) {
	return nullptr;
	}
	Vector<const ast::Parameter*, 8> params;
	for (auto pair : fn->TextureSamplerPairs()) {
	if (!pair.second) {
	continue;
	}
	InsertPair(pair, fn, &params);
	}
	for (auto pair : fn->TextureSamplerPairs()) {
	if (pair.second) {
	continue;
	}
	// Look for another pair with a non-null sampler.
	// NOTE: this is O(N^2) in the number of pairs, since
	// FindFullTextureSamplerPair() also loops over all pairs. If this proves
	// problematic, it could be optimized.
	if (const sem::VariablePair* fullPair =
	FindFullTextureSamplerPair(pair.first, fn)) {
	if (IsGlobal(pair)) {
	global_combined_texture_samplers_[pair] =
	global_combined_texture_samplers_[*fullPair];
	} else {
	auto* var = function_combined_texture_samplers_[fn][*fullPair];
	function_combined_texture_samplers_[fn][pair] = var;
	}
	} else {
	InsertPair(pair, fn, &params);
	}
	}
	// Filter out separate textures and samplers from the original
	// function signature.
	for (auto* param : fn->Parameters()) {
	if (!param->Type()->IsAnyOf<core::type::Texture, core::type::Sampler>()) {
	params.Push(ctx.Clone(param->Declaration()));
	}
	}
	// Create a new function signature that differs only in the parameter
	// list.
	auto name = ctx.Clone(ast_fn->name);
	auto return_type = ctx.Clone(ast_fn->return_type);
	auto* body = ctx.Clone(ast_fn->body);
	auto attributes = ctx.Clone(ast_fn->attributes);
	auto return_type_attributes = ctx.Clone(ast_fn->return_type_attributes);
	return ctx.dst->create<ast::Function>(name, params, return_type, body,
	std::move(attributes),
	std::move(return_type_attributes));
	}
	return nullptr;
	});

	// Replace all function call expressions containing texture or
	// sampler parameters to use the current function's combined samplers or
	// the combined global samplers, as appropriate.
	ctx.ReplaceAll([&](const ast::CallExpression* expr) -> const ast::Expression* {
	if (auto* call = sem.Get(expr)->UnwrapMaterialize()->As<sem::Call>()) {
	Vector<const ast::Expression*, 8> args;
	// Replace all texture builtin calls.
	if (auto* builtin = call->Target()->As<sem::BuiltinFn>()) {
	const auto& signature = builtin->Signature();
	auto sampler_index = signature.IndexOf(core::ParameterUsage::kSampler);
	auto texture_index = signature.IndexOf(core::ParameterUsage::kTexture);
	if (texture_index == -1) {
	return nullptr;
	}
	const sem::ValueExpression* texture =
	call->Arguments()[static_cast<size_t>(texture_index)];
	// We don't want to combine storage textures with anything, since
	// they never have associated samplers in GLSL.
	if (texture->Type()->UnwrapRef()->Is<core::type::StorageTexture>()) {
	return nullptr;
	}
	const sem::ValueExpression* sampler =
	sampler_index != -1 ? call->Arguments()[static_cast<size_t>(sampler_index)]
	: nullptr;
	auto* texture_var = texture->UnwrapLoad()->As<sem::VariableUser>()->Variable();
	auto* sampler_var =
	sampler ? sampler->UnwrapLoad()->As<sem::VariableUser>()->Variable()
	: nullptr;
	sem::VariablePair new_pair(texture_var, sampler_var);
	for (auto* arg : expr->args) {
	auto* type = ctx.src->TypeOf(arg)->UnwrapRef();
	if (type->Is<core::type::Texture>()) {
	const ast::Variable* var =
	IsGlobal(new_pair)
	? global_combined_texture_samplers_[new_pair]
	: function_combined_texture_samplers_[call->Stmt()->Function()]
	[new_pair];
	args.Push(ctx.dst->Expr(var->name->symbol));
	} else if (auto* sampler_type = type->As<core::type::Sampler>()) {
	core::type::SamplerKind kind = sampler_type->kind();
	int index = (kind == core::type::SamplerKind::kSampler) ? 0 : 1;
	const ast::Variable*& p = placeholder_samplers_[index];
	if (!p) {
	p = CreatePlaceholder(kind);
	}
	args.Push(ctx.dst->Expr(p->name->symbol));
	} else {
	args.Push(ctx.Clone(arg));
	}
	}
	const ast::Expression* value = ctx.dst->Call(ctx.Clone(expr->target), args);
	if (builtin->Fn() == wgsl::BuiltinFn::kTextureLoad &&
	texture_var->Type()->UnwrapRef()->Is<core::type::DepthTexture>() &&
	!call->Stmt()->Declaration()->Is<ast::CallStatement>()) {
	value = ctx.dst->MemberAccessor(value, "x");
	}
	return value;
	}
	// Replace all function calls.
	if (auto* callee = call->Target()->As<sem::Function>()) {
	for (auto pair : callee->TextureSamplerPairs()) {
	// Global pairs used by the callee do not require a function
	// parameter at the call site.
	if (IsGlobal(pair)) {
	continue;
	}
	// Texture-only pairs do not require a function parameter if they've been
	// replaced by a real pair.
	if (!pair.second && FindFullTextureSamplerPair(pair.first, callee)) {
	continue;
	}

	const sem::Variable* texture_var = pair.first;
	const sem::Variable* sampler_var = pair.second;
	if (auto* param = texture_var->As<sem::Parameter>()) {
	const sem::ValueExpression* texture = call->Arguments()[param->Index()];
	texture_var =
	texture->UnwrapLoad()->As<sem::VariableUser>()->Variable();
	}
	if (sampler_var) {
	if (auto* param = sampler_var->As<sem::Parameter>()) {
	const sem::ValueExpression* sampler =
	call->Arguments()[param->Index()];
	sampler_var =
	sampler->UnwrapLoad()->As<sem::VariableUser>()->Variable();
	}
	}
	sem::VariablePair new_pair(texture_var, sampler_var);
	// If both texture and sampler are (now) global, pass that
	// global variable to the callee. Otherwise use the caller's
	// function parameter for this pair.
	const ast::Variable* var =
	IsGlobal(new_pair)
	? global_combined_texture_samplers_[new_pair]
	: function_combined_texture_samplers_[call->Stmt()->Function()]
	[new_pair];
	auto* arg = ctx.dst->Expr(var->name->symbol);
	args.Push(arg);
	}
	// Append all of the remaining non-texture and non-sampler
	// parameters.
	for (auto* arg : expr->args) {
	if (!ctx.src->TypeOf(arg)
	->UnwrapRef()
	->IsAnyOf<core::type::Texture, core::type::Sampler>()) {
	args.Push(ctx.Clone(arg));
	}
	}
	return ctx.dst->Call(ctx.Clone(expr->target), args);
	}
	}
	return nullptr;
	});

	ctx.Clone();
	return resolver::Resolve(b);
	}
	};

	CombineSamplers::CombineSamplers() = default;

	CombineSamplers::~CombineSamplers() = default;

	ast::transform::Transform::ApplyResult CombineSamplers::Apply(const Program& src,
	const ast::transform::DataMap& inputs,
	ast::transform::DataMap&) const {
	auto* binding_info = inputs.Get<BindingInfo>();
	if (!binding_info) {
	ProgramBuilder b;
	b.Diagnostics().add_error(diag::System::Transform,
	"missing transform data for " + std::string(TypeInfo().name));
	return resolver::Resolve(b);
	}

	return State(src, binding_info).Run();
	}

	} // namespace tint::glsl::writer