src/transform/spirv.cc - tint.git - Git at Google

 // Copyright 2020 The Tint Authors.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 #include "src/transform/spirv.h"

 #include <string>
 #include <utility>

 #include "src/ast/call_statement.h"
 #include "src/ast/return_statement.h"
 #include "src/ast/stage_decoration.h"
 #include "src/program_builder.h"
 #include "src/sem/function.h"
 #include "src/sem/statement.h"
 #include "src/sem/variable.h"

 namespace tint {
 namespace transform {

 Spirv::Spirv() = default;
 Spirv::~Spirv() = default;

 Output Spirv::Run(const Program* in, const DataMap&) {
   ProgramBuilder out;
   CloneContext ctx(&out, in);
   HandleEntryPointIOTypes(ctx);
   ctx.Clone();

   // TODO(jrprice): Look into combining these transforms into a single clone.
   Program tmp(std::move(out));

   ProgramBuilder out2;
   CloneContext ctx2(&out2, &tmp);
   HandleSampleMaskBuiltins(ctx2);
   AddEmptyEntryPoint(ctx2);
   ctx2.Clone();

   return Output{Program(std::move(out2))};
 }

 void Spirv::HandleEntryPointIOTypes(CloneContext& ctx) const {
   // Hoist entry point parameters, return values, and struct members out to
   // global variables. Declare and construct struct parameters in the function
   // body. Replace entry point return statements with calls to a function that
   // assigns the return value to the global output variables.
   //
   // Before:
   // ```
   // struct FragmentInput {
   //   [[builtin(sample_index)]] sample_index : u32;
   //   [[builtin(sample_mask)]] sample_mask : u32;
   // };
   // struct FragmentOutput {
   //   [[builtin(frag_depth)]] depth: f32;
   //   [[builtin(sample_mask)]] mask_out : u32;
   // };
   //
   // [[stage(fragment)]]
   // fn frag_main(
   //   [[builtin(position)]] coord : vec4<f32>,
   //   samples : FragmentInput
   // ) -> FragmentOutput {
   //   var output : FragmentOutput = FragmentOutput(1.0,
   //                                                samples.sample_mask);
   //   return output;
   // }
   // ```
   //
   // After:
   // ```
   // struct FragmentInput {
   //   sample_index : u32;
   //   sample_mask : u32;
   // };
   // struct FragmentOutput {
   //   depth: f32;
   //   mask_out : u32;
   // };
   //
   // [[builtin(position)]] var<in> coord : vec4<f32>,
   // [[builtin(sample_index)]] var<in> sample_index : u32,
   // [[builtin(sample_mask)]] var<in> sample_mask : u32,
   // [[builtin(frag_depth)]] var<out> depth: f32;
   // [[builtin(sample_mask)]] var<out> mask_out : u32;
   //
   // fn frag_main_ret(retval : FragmentOutput) {
   //   depth = reval.depth;
   //   mask_out = retval.mask_out;
   // }
   //
   // [[stage(fragment)]]
   // fn frag_main() {
   //   let samples : FragmentInput(sample_index, sample_mask);
   //   var output : FragmentOutput = FragmentOutput(1.0,
   //                                                samples.sample_mask);
   //   frag_main_ret(output);
   //   return;
   // }
   // ```

   // Strip entry point IO decorations from struct declarations.
   for (auto* ty : ctx.src->AST().ConstructedTypes()) {
     if (auto* struct_ty = ty->As<sem::StructType>()) {
       // Build new list of struct members without entry point IO decorations.
       ast::StructMemberList new_struct_members;
       for (auto* member : struct_ty->impl()->members()) {
         ast::DecorationList new_decorations = RemoveDecorations(
             &ctx, member->decorations(), [](const ast::Decoration* deco) {
               return deco
                   ->IsAnyOf<ast::BuiltinDecoration, ast::LocationDecoration>();
             });
         new_struct_members.push_back(
             ctx.dst->Member(ctx.Clone(member->symbol()),
                             ctx.Clone(member->type()), new_decorations));
       }

       // Redeclare the struct.
       auto new_struct_name = ctx.Clone(struct_ty->impl()->name());
       auto* new_struct =
           ctx.dst->create<sem::StructType>(ctx.dst->create<ast::Struct>(
               new_struct_name, new_struct_members,
               ctx.Clone(struct_ty->impl()->decorations())));
       ctx.Replace(struct_ty, new_struct);
     }
   }

   for (auto* func : ctx.src->AST().Functions()) {
     if (!func->IsEntryPoint()) {
       continue;
     }

     for (auto* param : func->params()) {
       Symbol new_var = HoistToInputVariables(
           ctx, func, ctx.src->Sem().Get(param)->Type(),
           ctx.src->Sem().Get(param)->DeclaredType(), param->decorations());

       // Replace all uses of the function parameter with the new variable.
       for (auto* user : ctx.src->Sem().Get(param)->Users()) {
         ctx.Replace<ast::Expression>(user->Declaration(),
                                      ctx.dst->Expr(new_var));
       }
     }

     if (!func->return_type()->Is<sem::Void>()) {
       ast::StatementList stores;
       auto store_value_symbol = ctx.dst->Sym();
       HoistToOutputVariables(
           ctx, func, func->return_type(), func->return_type(),
           func->return_type_decorations(), {}, store_value_symbol, stores);

       // Create a function that writes a return value to all output variables.
       auto* store_value =
           ctx.dst->Param(store_value_symbol, ctx.Clone(func->return_type()));
       auto return_func_symbol = ctx.dst->Sym();
       auto* return_func = ctx.dst->create<ast::Function>(
           return_func_symbol, ast::VariableList{store_value},
           ctx.dst->ty.void_(), ctx.dst->create<ast::BlockStatement>(stores),
           ast::DecorationList{}, ast::DecorationList{});
       ctx.InsertBefore(ctx.src->AST().GlobalDeclarations(), func, return_func);

       // Replace all return statements with calls to the output function.
       auto* sem_func = ctx.src->Sem().Get(func);
       for (auto* ret : sem_func->ReturnStatements()) {
         auto* ret_sem = ctx.src->Sem().Get(ret);
         auto* call = ctx.dst->Call(return_func_symbol, ctx.Clone(ret->value()));
         ctx.InsertBefore(ret_sem->Block()->statements(), ret,
                          ctx.dst->create<ast::CallStatement>(call));
         ctx.Replace(ret, ctx.dst->Return());
       }
     }

     // Rewrite the function header to remove the parameters and return value.
     auto* new_func = ctx.dst->create<ast::Function>(
         func->source(), ctx.Clone(func->symbol()), ast::VariableList{},
         ctx.dst->ty.void_(), ctx.Clone(func->body()),
         ctx.Clone(func->decorations()), ast::DecorationList{});
     ctx.Replace(func, new_func);
   }
 }

 void Spirv::HandleSampleMaskBuiltins(CloneContext& ctx) const {
   // Find global variables decorated with [[builtin(sample_mask)]] and
   // change their type from `u32` to `array<u32, 1>`, as required by Vulkan.
   //
   // Before:
   // ```
   // [[builtin(sample_mask)]] var<out> mask_out : u32;
   // fn main() {
   //   mask_out = 1u;
   // }
   // ```
   // After:
   // ```
   // [[builtin(sample_mask)]] var<out> mask_out : array<u32, 1>;
   // fn main() {
   //   mask_out[0] = 1u;
   // }
   // ```

   for (auto* var : ctx.src->AST().GlobalVariables()) {
     for (auto* deco : var->decorations()) {
       if (auto* builtin = deco->As<ast::BuiltinDecoration>()) {
         if (builtin->value() != ast::Builtin::kSampleMask &&
             builtin->value() != ast::Builtin::kSampleMaskIn &&
             builtin->value() != ast::Builtin::kSampleMaskOut) {
           continue;
         }

         // Use the same name as the old variable.
         auto var_name = ctx.Clone(var->symbol());
         // Use `array<u32, 1>` for the new variable.
         auto type = ctx.dst->ty.array(ctx.dst->ty.u32(), 1u);
         // Create the new variable.
         auto* var_arr = ctx.dst->Var(var->source(), var_name, type,
                                      var->declared_storage_class(), nullptr,
                                      ctx.Clone(var->decorations()));
         // Replace the variable with the arrayed version.
         ctx.Replace(var, var_arr);

         // Replace all uses of the old variable with `var_arr[0]`.
         for (auto* user : ctx.src->Sem().Get(var)->Users()) {
           auto* new_ident = ctx.dst->IndexAccessor(
               ctx.dst->Expr(var_arr->symbol()), ctx.dst->Expr(0));
           ctx.Replace<ast::Expression>(user->Declaration(), new_ident);
         }
       }
     }
   }
 }

 void Spirv::AddEmptyEntryPoint(CloneContext& ctx) const {
   for (auto* func : ctx.src->AST().Functions()) {
     if (func->IsEntryPoint()) {
       return;
     }
   }
   ctx.dst->Func("_tint_unused_entry_point", {}, ctx.dst->ty.void_(), {},
                 {ctx.dst->Stage(ast::PipelineStage::kCompute)});
 }

 Symbol Spirv::HoistToInputVariables(
     CloneContext& ctx,
     const ast::Function* func,
     sem::Type* ty,
     sem::Type* declared_ty,
     const ast::DecorationList& decorations) const {
   if (!ty->Is<sem::StructType>()) {
     // Base case: create a global variable and return.
     ast::DecorationList new_decorations =
         RemoveDecorations(&ctx, decorations, [](const ast::Decoration* deco) {
           return !deco->IsAnyOf<ast::BuiltinDecoration,
                                 ast::LocationDecoration>();
         });
     auto global_var_symbol = ctx.dst->Sym();
     auto* global_var =
         ctx.dst->Var(global_var_symbol, ctx.Clone(declared_ty),
                      ast::StorageClass::kInput, nullptr, new_decorations);
     ctx.InsertBefore(ctx.src->AST().GlobalDeclarations(), func, global_var);
     return global_var_symbol;
   }

   // Recurse into struct members and build the initializer list.
   std::vector<Symbol> init_value_names;
   auto* struct_ty = ty->As<sem::StructType>();
   for (auto* member : struct_ty->impl()->members()) {
     auto member_var = HoistToInputVariables(
         ctx, func, member->type(), member->type(), member->decorations());
     init_value_names.emplace_back(member_var);
   }

   auto func_var_symbol = ctx.dst->Sym();
   if (func->body()->empty()) {
     // The return value should never get used.
     return func_var_symbol;
   }

   ast::ExpressionList init_values;
   for (auto name : init_value_names) {
     init_values.push_back(ctx.dst->Expr(name));
   }

   // Create a function-scope variable for the struct.
   auto* initializer = ctx.dst->Construct(ctx.Clone(declared_ty), init_values);
   auto* func_var =
       ctx.dst->Const(func_var_symbol, ctx.Clone(declared_ty), initializer);
   ctx.InsertBefore(func->body()->statements(), *func->body()->begin(),
                    ctx.dst->WrapInStatement(func_var));
   return func_var_symbol;
 }

 void Spirv::HoistToOutputVariables(CloneContext& ctx,
                                    const ast::Function* func,
                                    sem::Type* ty,
                                    sem::Type* declared_ty,
                                    const ast::DecorationList& decorations,
                                    std::vector<Symbol> member_accesses,
                                    Symbol store_value,
                                    ast::StatementList& stores) const {
   // Base case.
   if (!ty->Is<sem::StructType>()) {
     // Create a global variable.
     ast::DecorationList new_decorations =
         RemoveDecorations(&ctx, decorations, [](const ast::Decoration* deco) {
           return !deco->IsAnyOf<ast::BuiltinDecoration,
                                 ast::LocationDecoration>();
         });
     auto global_var_symbol = ctx.dst->Sym();
     auto* global_var =
         ctx.dst->Var(global_var_symbol, ctx.Clone(declared_ty),
                      ast::StorageClass::kOutput, nullptr, new_decorations);
     ctx.InsertBefore(ctx.src->AST().GlobalDeclarations(), func, global_var);

     // Special case for PointSize. The EmitVertexPointSize transform will
     // produce a struct containing a member with the [[builtin(pointsize)]]
     // attribute. The SPIR-V reader currently requires that a variable decorated
     // with PointSize is assigned a _literal_ 1.0 value, so generate that
     // assignment here to prevent the RHS from using a non-literal expression.
     if (auto* builtin =
             ast::GetDecoration<ast::BuiltinDecoration>(new_decorations)) {
       if (builtin->value() == ast::Builtin::kPointSize) {
         stores.push_back(ctx.dst->Assign(ctx.dst->Expr(global_var_symbol),
                                          ctx.dst->Expr(1.f)));
         return;
       }
     }

     // Create the assignment instruction.
     ast::Expression* rhs = ctx.dst->Expr(store_value);
     for (auto member : member_accesses) {
       rhs = ctx.dst->MemberAccessor(rhs, member);
     }
     stores.push_back(ctx.dst->Assign(ctx.dst->Expr(global_var_symbol), rhs));

     return;
   }

   // Recurse into struct members.
   auto* struct_ty = ty->As<sem::StructType>();
   for (auto* member : struct_ty->impl()->members()) {
     member_accesses.push_back(ctx.Clone(member->symbol()));
     HoistToOutputVariables(ctx, func, member->type(), member->type(),
                            member->decorations(), member_accesses, store_value,
                            stores);
     member_accesses.pop_back();
   }
 }

 }  // namespace transform
 }  // namespace tint
	// Copyright 2020 The Tint Authors.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.

	#include "src/transform/spirv.h"

	#include <string>
	#include <utility>

	#include "src/ast/call_statement.h"
	#include "src/ast/return_statement.h"
	#include "src/ast/stage_decoration.h"
	#include "src/program_builder.h"
	#include "src/sem/function.h"
	#include "src/sem/statement.h"
	#include "src/sem/variable.h"

	namespace tint {
	namespace transform {

	Spirv::Spirv() = default;
	Spirv::~Spirv() = default;

	Output Spirv::Run(const Program* in, const DataMap&) {
	ProgramBuilder out;
	CloneContext ctx(&out, in);
	HandleEntryPointIOTypes(ctx);
	ctx.Clone();

	// TODO(jrprice): Look into combining these transforms into a single clone.
	Program tmp(std::move(out));

	ProgramBuilder out2;
	CloneContext ctx2(&out2, &tmp);
	HandleSampleMaskBuiltins(ctx2);
	AddEmptyEntryPoint(ctx2);
	ctx2.Clone();

	return Output{Program(std::move(out2))};
	}

	void Spirv::HandleEntryPointIOTypes(CloneContext& ctx) const {
	// Hoist entry point parameters, return values, and struct members out to
	// global variables. Declare and construct struct parameters in the function
	// body. Replace entry point return statements with calls to a function that
	// assigns the return value to the global output variables.
	//
	// Before:
	// ```
	// struct FragmentInput {
	// [[builtin(sample_index)]] sample_index : u32;
	// [[builtin(sample_mask)]] sample_mask : u32;
	// };
	// struct FragmentOutput {
	// [[builtin(frag_depth)]] depth: f32;
	// [[builtin(sample_mask)]] mask_out : u32;
	// };
	//
	// [[stage(fragment)]]
	// fn frag_main(
	// [[builtin(position)]] coord : vec4<f32>,
	// samples : FragmentInput
	// ) -> FragmentOutput {
	// var output : FragmentOutput = FragmentOutput(1.0,
	// samples.sample_mask);
	// return output;
	// }
	// ```
	//
	// After:
	// ```
	// struct FragmentInput {
	// sample_index : u32;
	// sample_mask : u32;
	// };
	// struct FragmentOutput {
	// depth: f32;
	// mask_out : u32;
	// };
	//
	// [[builtin(position)]] var<in> coord : vec4<f32>,
	// [[builtin(sample_index)]] var<in> sample_index : u32,
	// [[builtin(sample_mask)]] var<in> sample_mask : u32,
	// [[builtin(frag_depth)]] var<out> depth: f32;
	// [[builtin(sample_mask)]] var<out> mask_out : u32;
	//
	// fn frag_main_ret(retval : FragmentOutput) {
	// depth = reval.depth;
	// mask_out = retval.mask_out;
	// }
	//
	// [[stage(fragment)]]
	// fn frag_main() {
	// let samples : FragmentInput(sample_index, sample_mask);
	// var output : FragmentOutput = FragmentOutput(1.0,
	// samples.sample_mask);
	// frag_main_ret(output);
	// return;
	// }
	// ```

	// Strip entry point IO decorations from struct declarations.
	for (auto* ty : ctx.src->AST().ConstructedTypes()) {
	if (auto* struct_ty = ty->As<sem::StructType>()) {
	// Build new list of struct members without entry point IO decorations.
	ast::StructMemberList new_struct_members;
	for (auto* member : struct_ty->impl()->members()) {
	ast::DecorationList new_decorations = RemoveDecorations(
	&ctx, member->decorations(), [](const ast::Decoration* deco) {
	return deco
	->IsAnyOf<ast::BuiltinDecoration, ast::LocationDecoration>();
	});
	new_struct_members.push_back(
	ctx.dst->Member(ctx.Clone(member->symbol()),
	ctx.Clone(member->type()), new_decorations));
	}

	// Redeclare the struct.
	auto new_struct_name = ctx.Clone(struct_ty->impl()->name());
	auto* new_struct =
	ctx.dst->create<sem::StructType>(ctx.dst->create<ast::Struct>(
	new_struct_name, new_struct_members,
	ctx.Clone(struct_ty->impl()->decorations())));
	ctx.Replace(struct_ty, new_struct);
	}
	}

	for (auto* func : ctx.src->AST().Functions()) {
	if (!func->IsEntryPoint()) {
	continue;
	}

	for (auto* param : func->params()) {
	Symbol new_var = HoistToInputVariables(
	ctx, func, ctx.src->Sem().Get(param)->Type(),
	ctx.src->Sem().Get(param)->DeclaredType(), param->decorations());

	// Replace all uses of the function parameter with the new variable.
	for (auto* user : ctx.src->Sem().Get(param)->Users()) {
	ctx.Replace<ast::Expression>(user->Declaration(),
	ctx.dst->Expr(new_var));
	}
	}

	if (!func->return_type()->Is<sem::Void>()) {
	ast::StatementList stores;
	auto store_value_symbol = ctx.dst->Sym();
	HoistToOutputVariables(
	ctx, func, func->return_type(), func->return_type(),
	func->return_type_decorations(), {}, store_value_symbol, stores);

	// Create a function that writes a return value to all output variables.
	auto* store_value =
	ctx.dst->Param(store_value_symbol, ctx.Clone(func->return_type()));
	auto return_func_symbol = ctx.dst->Sym();
	auto* return_func = ctx.dst->create<ast::Function>(
	return_func_symbol, ast::VariableList{store_value},
	ctx.dst->ty.void_(), ctx.dst->create<ast::BlockStatement>(stores),
	ast::DecorationList{}, ast::DecorationList{});
	ctx.InsertBefore(ctx.src->AST().GlobalDeclarations(), func, return_func);

	// Replace all return statements with calls to the output function.
	auto* sem_func = ctx.src->Sem().Get(func);
	for (auto* ret : sem_func->ReturnStatements()) {
	auto* ret_sem = ctx.src->Sem().Get(ret);
	auto* call = ctx.dst->Call(return_func_symbol, ctx.Clone(ret->value()));
	ctx.InsertBefore(ret_sem->Block()->statements(), ret,
	ctx.dst->create<ast::CallStatement>(call));
	ctx.Replace(ret, ctx.dst->Return());
	}
	}

	// Rewrite the function header to remove the parameters and return value.
	auto* new_func = ctx.dst->create<ast::Function>(
	func->source(), ctx.Clone(func->symbol()), ast::VariableList{},
	ctx.dst->ty.void_(), ctx.Clone(func->body()),
	ctx.Clone(func->decorations()), ast::DecorationList{});
	ctx.Replace(func, new_func);
	}
	}

	void Spirv::HandleSampleMaskBuiltins(CloneContext& ctx) const {
	// Find global variables decorated with [[builtin(sample_mask)]] and
	// change their type from `u32` to `array<u32, 1>`, as required by Vulkan.
	//
	// Before:
	// ```
	// [[builtin(sample_mask)]] var<out> mask_out : u32;
	// fn main() {
	// mask_out = 1u;
	// }
	// ```
	// After:
	// ```
	// [[builtin(sample_mask)]] var<out> mask_out : array<u32, 1>;
	// fn main() {
	// mask_out[0] = 1u;
	// }
	// ```

	for (auto* var : ctx.src->AST().GlobalVariables()) {
	for (auto* deco : var->decorations()) {
	if (auto* builtin = deco->As<ast::BuiltinDecoration>()) {
	if (builtin->value() != ast::Builtin::kSampleMask &&
	builtin->value() != ast::Builtin::kSampleMaskIn &&
	builtin->value() != ast::Builtin::kSampleMaskOut) {
	continue;
	}

	// Use the same name as the old variable.
	auto var_name = ctx.Clone(var->symbol());
	// Use `array<u32, 1>` for the new variable.
	auto type = ctx.dst->ty.array(ctx.dst->ty.u32(), 1u);
	// Create the new variable.
	auto* var_arr = ctx.dst->Var(var->source(), var_name, type,
	var->declared_storage_class(), nullptr,
	ctx.Clone(var->decorations()));
	// Replace the variable with the arrayed version.
	ctx.Replace(var, var_arr);

	// Replace all uses of the old variable with `var_arr[0]`.
	for (auto* user : ctx.src->Sem().Get(var)->Users()) {
	auto* new_ident = ctx.dst->IndexAccessor(
	ctx.dst->Expr(var_arr->symbol()), ctx.dst->Expr(0));
	ctx.Replace<ast::Expression>(user->Declaration(), new_ident);
	}
	}
	}
	}
	}

	void Spirv::AddEmptyEntryPoint(CloneContext& ctx) const {
	for (auto* func : ctx.src->AST().Functions()) {
	if (func->IsEntryPoint()) {
	return;
	}
	}
	ctx.dst->Func("_tint_unused_entry_point", {}, ctx.dst->ty.void_(), {},
	{ctx.dst->Stage(ast::PipelineStage::kCompute)});
	}

	Symbol Spirv::HoistToInputVariables(
	CloneContext& ctx,
	const ast::Function* func,
	sem::Type* ty,
	sem::Type* declared_ty,
	const ast::DecorationList& decorations) const {
	if (!ty->Is<sem::StructType>()) {
	// Base case: create a global variable and return.
	ast::DecorationList new_decorations =
	RemoveDecorations(&ctx, decorations, [](const ast::Decoration* deco) {
	return !deco->IsAnyOf<ast::BuiltinDecoration,
	ast::LocationDecoration>();
	});
	auto global_var_symbol = ctx.dst->Sym();
	auto* global_var =
	ctx.dst->Var(global_var_symbol, ctx.Clone(declared_ty),
	ast::StorageClass::kInput, nullptr, new_decorations);
	ctx.InsertBefore(ctx.src->AST().GlobalDeclarations(), func, global_var);
	return global_var_symbol;
	}

	// Recurse into struct members and build the initializer list.
	std::vector<Symbol> init_value_names;
	auto* struct_ty = ty->As<sem::StructType>();
	for (auto* member : struct_ty->impl()->members()) {
	auto member_var = HoistToInputVariables(
	ctx, func, member->type(), member->type(), member->decorations());
	init_value_names.emplace_back(member_var);
	}

	auto func_var_symbol = ctx.dst->Sym();
	if (func->body()->empty()) {
	// The return value should never get used.
	return func_var_symbol;
	}

	ast::ExpressionList init_values;
	for (auto name : init_value_names) {
	init_values.push_back(ctx.dst->Expr(name));
	}

	// Create a function-scope variable for the struct.
	auto* initializer = ctx.dst->Construct(ctx.Clone(declared_ty), init_values);
	auto* func_var =
	ctx.dst->Const(func_var_symbol, ctx.Clone(declared_ty), initializer);
	ctx.InsertBefore(func->body()->statements(), *func->body()->begin(),
	ctx.dst->WrapInStatement(func_var));
	return func_var_symbol;
	}

	void Spirv::HoistToOutputVariables(CloneContext& ctx,
	const ast::Function* func,
	sem::Type* ty,
	sem::Type* declared_ty,
	const ast::DecorationList& decorations,
	std::vector<Symbol> member_accesses,
	Symbol store_value,
	ast::StatementList& stores) const {
	// Base case.
	if (!ty->Is<sem::StructType>()) {
	// Create a global variable.
	ast::DecorationList new_decorations =
	RemoveDecorations(&ctx, decorations, [](const ast::Decoration* deco) {
	return !deco->IsAnyOf<ast::BuiltinDecoration,
	ast::LocationDecoration>();
	});
	auto global_var_symbol = ctx.dst->Sym();
	auto* global_var =
	ctx.dst->Var(global_var_symbol, ctx.Clone(declared_ty),
	ast::StorageClass::kOutput, nullptr, new_decorations);
	ctx.InsertBefore(ctx.src->AST().GlobalDeclarations(), func, global_var);

	// Special case for PointSize. The EmitVertexPointSize transform will
	// produce a struct containing a member with the [[builtin(pointsize)]]
	// attribute. The SPIR-V reader currently requires that a variable decorated
	// with PointSize is assigned a _literal_ 1.0 value, so generate that
	// assignment here to prevent the RHS from using a non-literal expression.
	if (auto* builtin =
	ast::GetDecoration<ast::BuiltinDecoration>(new_decorations)) {
	if (builtin->value() == ast::Builtin::kPointSize) {
	stores.push_back(ctx.dst->Assign(ctx.dst->Expr(global_var_symbol),
	ctx.dst->Expr(1.f)));
	return;
	}
	}

	// Create the assignment instruction.
	ast::Expression* rhs = ctx.dst->Expr(store_value);
	for (auto member : member_accesses) {
	rhs = ctx.dst->MemberAccessor(rhs, member);
	}
	stores.push_back(ctx.dst->Assign(ctx.dst->Expr(global_var_symbol), rhs));

	return;
	}

	// Recurse into struct members.
	auto* struct_ty = ty->As<sem::StructType>();
	for (auto* member : struct_ty->impl()->members()) {
	member_accesses.push_back(ctx.Clone(member->symbol()));
	HoistToOutputVariables(ctx, func, member->type(), member->type(),
	member->decorations(), member_accesses, store_value,
	stores);
	member_accesses.pop_back();
	}
	}

	} // namespace transform
	} // namespace tint