[msl-writer] Add builtin support

This CL extends module scoped variables to include support for builtins.

Bug: tint:8
Change-Id: I9e4363be32401bfdd45ad5d1727d9432aca206fe
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/24786
Reviewed-by: David Neto <dneto@google.com>

src/ast/decorated_variable.cc

@@ -35,6 +35,15 @@ bool DecoratedVariable::HasLocationDecoration() const {
   return false;
 }
 
+bool DecoratedVariable::HasBuiltinDecoration() const {
+  for (const auto& deco : decorations_) {
+    if (deco->IsBuiltin()) {
+      return true;
+    }
+  }
+  return false;
+}
+
 bool DecoratedVariable::IsDecorated() const {
   return true;
 }

src/ast/decorated_variable.h

@@ -47,6 +47,8 @@ class DecoratedVariable : public Variable {
 
   /// @returns true if the decorations include a LocationDecoration
   bool HasLocationDecoration() const;
+  /// @returns true if the deocrations include a BuiltinDecoration
+  bool HasBuiltinDecoration() const;
 
   /// @returns true if this is a decorated variable
   bool IsDecorated() const override;

src/writer/msl/generator_impl.cc

@@ -333,11 +333,26 @@ bool GeneratorImpl::EmitCall(ast::CallExpression* expr) {
       if (!first) {
         out_ << ", ";
       }
-      out_ << var_name;
       first = false;
+      out_ << var_name;
     }
 
-    // TODO(dsinclair): Emit builtins
+    auto* func = module_->FindFunctionByName(ident->name());
+    if (func == nullptr) {
+      error_ = "Unable to find function: " + name;
+      return false;
+    }
+    for (const auto& data : func->referenced_builtin_variables()) {
+      auto* var = data.first;
+      if (var->storage_class() != ast::StorageClass::kInput) {
+        continue;
+      }
+      if (!first) {
+        out_ << ", ";
+      }
+      first = false;
+      out_ << var->name();
+    }
 
     const auto& params = expr->params();
     for (const auto& param : params) {
@@ -517,15 +532,25 @@ bool GeneratorImpl::EmitEntryPointData(ast::EntryPoint* ep) {
   }
 
   std::vector<std::pair<ast::Variable*, uint32_t>> in_locations;
-  std::vector<std::pair<ast::Variable*, uint32_t>> out_locations;
+  std::vector<std::pair<ast::Variable*, ast::VariableDecoration*>>
+      out_variables;
   for (auto data : func->referenced_location_variables()) {
     auto var = data.first;
-    auto locn_deco = data.second;
+    auto deco = data.second;
 
     if (var->storage_class() == ast::StorageClass::kInput) {
-      in_locations.push_back({var, locn_deco->value()});
+      in_locations.push_back({var, deco->value()});
     } else if (var->storage_class() == ast::StorageClass::kOutput) {
-      out_locations.push_back({var, locn_deco->value()});
+      out_variables.push_back({var, deco});
+    }
+  }
+
+  for (auto data : func->referenced_builtin_variables()) {
+    auto var = data.first;
+    auto deco = data.second;
+
+    if (var->storage_class() == ast::StorageClass::kOutput) {
+      out_variables.push_back({var, deco});
     }
   }
 
@@ -575,7 +600,7 @@ bool GeneratorImpl::EmitEntryPointData(ast::EntryPoint* ep) {
     out_ << "};" << std::endl << std::endl;
   }
 
-  if (!out_locations.empty()) {
+  if (!out_variables.empty()) {
     auto out_struct_name = generate_name(ep_name + "_" + kOutStructNameSuffix);
     auto out_var_name = generate_name(kTintStructOutVarPrefix);
     ep_name_to_out_data_[ep_name] = {out_struct_name, out_var_name};
@@ -584,9 +609,9 @@ bool GeneratorImpl::EmitEntryPointData(ast::EntryPoint* ep) {
     out_ << "struct " << out_struct_name << " {" << std::endl;
 
     increment_indent();
-    for (auto& data : out_locations) {
+    for (auto& data : out_variables) {
       auto* var = data.first;
-      uint32_t loc = data.second;
+      auto* deco = data.second;
 
       make_indent();
       if (!EmitType(var->type(), var->name())) {
@@ -594,6 +619,9 @@ bool GeneratorImpl::EmitEntryPointData(ast::EntryPoint* ep) {
       }
 
       out_ << " " << var->name() << " [[";
+
+      if (deco->IsLocation()) {
+        auto loc = deco->AsLocation()->value();
         if (ep->stage() == ast::PipelineStage::kVertex) {
           out_ << "user(locn" << loc << ")";
         } else if (ep->stage() == ast::PipelineStage::kFragment) {
@@ -602,6 +630,17 @@ bool GeneratorImpl::EmitEntryPointData(ast::EntryPoint* ep) {
           error_ = "invalid location variable for pipeline stage";
           return false;
         }
+      } else if (deco->IsBuiltin()) {
+        auto attr = builtin_to_attribute(deco->AsBuiltin()->value());
+        if (attr.empty()) {
+          error_ = "unsupported builtin";
+          return false;
+        }
+        out_ << attr;
+      } else {
+        error_ = "unsupported variable decoration for entry point output";
+        return false;
+      }
       out_ << "]];" << std::endl;
     }
     decrement_indent();
@@ -739,7 +778,22 @@ bool GeneratorImpl::EmitFunctionInternal(ast::Function* func,
     }
   }
 
-  // TODO(dsinclair): Handle any entry point builtin params used here
+  for (const auto& data : func->referenced_builtin_variables()) {
+    auto* var = data.first;
+    if (var->storage_class() != ast::StorageClass::kInput) {
+      continue;
+    }
+    if (!first) {
+      out_ << ", ";
+    }
+    first = false;
+
+    out_ << "thread ";
+    if (!EmitType(var->type(), "")) {
+      return false;
+    }
+    out_ << "& " << var->name();
+  }
 
   // TODO(dsinclair): Binding/Set inputs
 
@@ -771,6 +825,41 @@ bool GeneratorImpl::EmitFunctionInternal(ast::Function* func,
   return true;
 }
 
+std::string GeneratorImpl::builtin_to_attribute(ast::Builtin builtin) const {
+  switch (builtin) {
+    case ast::Builtin::kPosition:
+      return "position";
+    case ast::Builtin::kVertexIdx:
+      return "vertex_id";
+    case ast::Builtin::kInstanceIdx:
+      return "instance_id";
+    case ast::Builtin::kFrontFacing:
+      return "front_facing";
+    case ast::Builtin::kFragCoord:
+      return "position";
+    case ast::Builtin::kFragDepth:
+      return "depth(any)";
+    // TODO(dsinclair): Ignore for now, I believe it will be removed from WGSL
+    // https://github.com/gpuweb/gpuweb/issues/920
+    case ast::Builtin::kNumWorkgroups:
+      return "";
+    // TODO(dsinclair): Ignore for now. This has been removed as a builtin
+    // in the spec. Need to update Tint to match.
+    // https://github.com/gpuweb/gpuweb/pull/824
+    case ast::Builtin::kWorkgroupSize:
+      return "";
+    case ast::Builtin::kLocalInvocationId:
+      return "thread_position_in_threadgroup";
+    case ast::Builtin::kLocalInvocationIdx:
+      return "thread_index_in_threadgroup";
+    case ast::Builtin::kGlobalInvocationId:
+      return "thread_position_in_grid";
+    default:
+      break;
+  }
+  return "";
+}
+
 bool GeneratorImpl::EmitEntryPointFunction(ast::EntryPoint* ep) {
   make_indent();
 
@@ -799,13 +888,38 @@ bool GeneratorImpl::EmitEntryPointFunction(ast::EntryPoint* ep) {
   }
   out_ << " " << namer_.NameFor(current_ep_name_) << "(";
 
+  bool first = true;
   auto in_data = ep_name_to_in_data_.find(current_ep_name_);
   if (in_data != ep_name_to_in_data_.end()) {
     out_ << in_data->second.struct_name << " " << in_data->second.var_name
          << " [[stage_in]]";
+    first = false;
   }
 
-  // TODO(dsinclair): Output other builtin inputs
+  for (auto data : func->referenced_builtin_variables()) {
+    auto* var = data.first;
+    if (var->storage_class() != ast::StorageClass::kInput) {
+      continue;
+    }
+
+    if (!first) {
+      out_ << ", ";
+    }
+    first = false;
+
+    auto* builtin = data.second;
+
+    if (!EmitType(var->type(), "")) {
+      return false;
+    }
+
+    auto attr = builtin_to_attribute(builtin->value());
+    if (attr.empty()) {
+      error_ = "unknown builtin";
+      return false;
+    }
+    out_ << " " << var->name() << " [[" << attr << "]]";
+  }
 
   // TODO(dsinclair): Binding/Set inputs
 
@@ -845,9 +959,14 @@ bool GeneratorImpl::EmitIdentifier(ast::IdentifierExpression* expr) {
 
   ast::Variable* var = nullptr;
   if (global_variables_.get(ident->name(), &var)) {
-    if (var->IsDecorated() && var->AsDecorated()->HasLocationDecoration() &&
+    bool in_or_out_struct_has_location =
+        var->IsDecorated() && var->AsDecorated()->HasLocationDecoration() &&
         (var->storage_class() == ast::StorageClass::kInput ||
-         var->storage_class() == ast::StorageClass::kOutput)) {
+         var->storage_class() == ast::StorageClass::kOutput);
+    bool in_struct_has_builtin =
+        var->IsDecorated() && var->AsDecorated()->HasBuiltinDecoration() &&
+        var->storage_class() == ast::StorageClass::kOutput;
+    if (in_or_out_struct_has_location || in_struct_has_builtin) {
       auto var_type = var->storage_class() == ast::StorageClass::kInput
                           ? VarType::kIn
                           : VarType::kOut;

src/writer/msl/generator_impl.h

@@ -198,6 +198,11 @@ class GeneratorImpl : public TextGenerator {
   /// @returns the name
   std::string generate_name(const std::string& prefix);
 
+  /// Converts a builtin to an attribute name
+  /// @param builtin the builtin to convert
+  /// @returns the string name of the builtin or blank on error
+  std::string builtin_to_attribute(ast::Builtin builtin) const;
+
   /// @returns the namer for testing
   Namer* namer_for_testing() { return &namer_; }
 

src/writer/msl/generator_impl_call_test.cc

@@ -16,7 +16,10 @@
 
 #include "gtest/gtest.h"
 #include "src/ast/call_expression.h"
+#include "src/ast/function.h"
 #include "src/ast/identifier_expression.h"
+#include "src/ast/module.h"
+#include "src/ast/type/void_type.h"
 #include "src/writer/msl/generator_impl.h"
 
 namespace tint {
@@ -27,22 +30,42 @@ namespace {
 using MslGeneratorImplTest = testing::Test;
 
 TEST_F(MslGeneratorImplTest, EmitExpression_Call_WithoutParams) {
+  ast::type::VoidType void_type;
+
   auto id = std::make_unique<ast::IdentifierExpression>("my_func");
   ast::CallExpression call(std::move(id), {});
 
+  auto func = std::make_unique<ast::Function>("my_func", ast::VariableList{},
+                                              &void_type);
+
+  ast::Module m;
+  m.AddFunction(std::move(func));
+
   GeneratorImpl g;
+  g.set_module_for_testing(&m);
+
   ASSERT_TRUE(g.EmitExpression(&call)) << g.error();
   EXPECT_EQ(g.result(), "my_func()");
 }
 
 TEST_F(MslGeneratorImplTest, EmitExpression_Call_WithParams) {
+  ast::type::VoidType void_type;
+
   auto id = std::make_unique<ast::IdentifierExpression>("my_func");
   ast::ExpressionList params;
   params.push_back(std::make_unique<ast::IdentifierExpression>("param1"));
   params.push_back(std::make_unique<ast::IdentifierExpression>("param2"));
   ast::CallExpression call(std::move(id), std::move(params));
 
+  auto func = std::make_unique<ast::Function>("my_func", ast::VariableList{},
+                                              &void_type);
+
+  ast::Module m;
+  m.AddFunction(std::move(func));
+
   GeneratorImpl g;
+  g.set_module_for_testing(&m);
+
   ASSERT_TRUE(g.EmitExpression(&call)) << g.error();
   EXPECT_EQ(g.result(), "my_func(param1, param2)");
 }

src/writer/msl/generator_impl_entry_point_test.cc

@@ -18,9 +18,12 @@
 #include "src/ast/entry_point.h"
 #include "src/ast/identifier_expression.h"
 #include "src/ast/location_decoration.h"
+#include "src/ast/member_accessor_expression.h"
 #include "src/ast/module.h"
 #include "src/ast/type/f32_type.h"
 #include "src/ast/type/i32_type.h"
+#include "src/ast/type/vector_type.h"
+#include "src/ast/type/void_type.h"
 #include "src/ast/variable.h"
 #include "src/context.h"
 #include "src/type_determiner.h"
@@ -419,6 +422,78 @@ TEST_F(MslGeneratorImplTest, EmitEntryPointData_Compute_Output) {
   EXPECT_EQ(g.error(), R"(invalid location variable for pipeline stage)");
 }
 
+TEST_F(MslGeneratorImplTest, EmitEntryPointData_Builtins) {
+  // Output builtins go in the output struct, input builtins will be passed
+  // as input parameters to the entry point function.
+
+  // [[builtin frag_coord]] var<in> coord : vec4<f32>;
+  // [[builtin frag_depth]] var<out> depth : f32;
+  //
+  // struct main_out {
+  //   float depth [[depth(any)]];
+  // };
+
+  ast::type::F32Type f32;
+  ast::type::VoidType void_type;
+  ast::type::VectorType vec4(&f32, 4);
+
+  auto coord_var =
+      std::make_unique<ast::DecoratedVariable>(std::make_unique<ast::Variable>(
+          "coord", ast::StorageClass::kInput, &vec4));
+
+  ast::VariableDecorationList decos;
+  decos.push_back(
+      std::make_unique<ast::BuiltinDecoration>(ast::Builtin::kFragCoord));
+  coord_var->set_decorations(std::move(decos));
+
+  auto depth_var =
+      std::make_unique<ast::DecoratedVariable>(std::make_unique<ast::Variable>(
+          "depth", ast::StorageClass::kOutput, &f32));
+  decos.push_back(
+      std::make_unique<ast::BuiltinDecoration>(ast::Builtin::kFragDepth));
+  depth_var->set_decorations(std::move(decos));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  td.RegisterVariableForTesting(coord_var.get());
+  td.RegisterVariableForTesting(depth_var.get());
+
+  mod.AddGlobalVariable(std::move(coord_var));
+  mod.AddGlobalVariable(std::move(depth_var));
+
+  ast::VariableList params;
+  auto func = std::make_unique<ast::Function>("frag_main", std::move(params),
+                                              &void_type);
+
+  ast::StatementList body;
+  body.push_back(std::make_unique<ast::AssignmentStatement>(
+      std::make_unique<ast::IdentifierExpression>("depth"),
+      std::make_unique<ast::MemberAccessorExpression>(
+          std::make_unique<ast::IdentifierExpression>("coord"),
+          std::make_unique<ast::IdentifierExpression>("x"))));
+  func->set_body(std::move(body));
+
+  mod.AddFunction(std::move(func));
+
+  auto ep = std::make_unique<ast::EntryPoint>(ast::PipelineStage::kFragment,
+                                              "main", "frag_main");
+  auto* ep_ptr = ep.get();
+
+  mod.AddEntryPoint(std::move(ep));
+
+  ASSERT_TRUE(td.Determine()) << td.error();
+
+  GeneratorImpl g;
+  g.set_module_for_testing(&mod);
+  ASSERT_TRUE(g.EmitEntryPointData(ep_ptr)) << g.error();
+  EXPECT_EQ(g.result(), R"(struct main_out {
+  float depth [[depth(any)]];
+};
+
+)");
+}
+
 }  // namespace
 }  // namespace msl
 }  // namespace writer

src/writer/msl/generator_impl_function_test.cc

@@ -22,6 +22,7 @@
 #include "src/ast/identifier_expression.h"
 #include "src/ast/if_statement.h"
 #include "src/ast/location_decoration.h"
+#include "src/ast/member_accessor_expression.h"
 #include "src/ast/module.h"
 #include "src/ast/return_statement.h"
 #include "src/ast/scalar_constructor_expression.h"
@@ -29,6 +30,7 @@
 #include "src/ast/type/array_type.h"
 #include "src/ast/type/f32_type.h"
 #include "src/ast/type/i32_type.h"
+#include "src/ast/type/vector_type.h"
 #include "src/ast/type/void_type.h"
 #include "src/ast/variable.h"
 #include "src/ast/variable_decl_statement.h"
@@ -216,8 +218,76 @@ fragment frag_main_out frag_main(frag_main_in tint_in [[stage_in]]) {
 )");
 }
 
+TEST_F(MslGeneratorImplTest, Emit_Function_EntryPoint_WithInOut_Builtins) {
+  ast::type::VoidType void_type;
+  ast::type::F32Type f32;
+  ast::type::VectorType vec4(&f32, 4);
+
+  auto coord_var =
+      std::make_unique<ast::DecoratedVariable>(std::make_unique<ast::Variable>(
+          "coord", ast::StorageClass::kInput, &vec4));
+
+  ast::VariableDecorationList decos;
+  decos.push_back(
+      std::make_unique<ast::BuiltinDecoration>(ast::Builtin::kFragCoord));
+  coord_var->set_decorations(std::move(decos));
+
+  auto depth_var =
+      std::make_unique<ast::DecoratedVariable>(std::make_unique<ast::Variable>(
+          "depth", ast::StorageClass::kOutput, &f32));
+  decos.push_back(
+      std::make_unique<ast::BuiltinDecoration>(ast::Builtin::kFragDepth));
+  depth_var->set_decorations(std::move(decos));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  td.RegisterVariableForTesting(coord_var.get());
+  td.RegisterVariableForTesting(depth_var.get());
+
+  mod.AddGlobalVariable(std::move(coord_var));
+  mod.AddGlobalVariable(std::move(depth_var));
+
+  ast::VariableList params;
+  auto func = std::make_unique<ast::Function>("frag_main", std::move(params),
+                                              &void_type);
+
+  ast::StatementList body;
+  body.push_back(std::make_unique<ast::AssignmentStatement>(
+      std::make_unique<ast::IdentifierExpression>("depth"),
+      std::make_unique<ast::MemberAccessorExpression>(
+          std::make_unique<ast::IdentifierExpression>("coord"),
+          std::make_unique<ast::IdentifierExpression>("x"))));
+  body.push_back(std::make_unique<ast::ReturnStatement>());
+  func->set_body(std::move(body));
+
+  mod.AddFunction(std::move(func));
+
+  auto ep = std::make_unique<ast::EntryPoint>(ast::PipelineStage::kFragment, "",
+                                              "frag_main");
+  mod.AddEntryPoint(std::move(ep));
+
+  ASSERT_TRUE(td.Determine()) << td.error();
+
+  GeneratorImpl g;
+  ASSERT_TRUE(g.Generate(mod)) << g.error();
+  EXPECT_EQ(g.result(), R"(#include <metal_stdlib>
+
+struct frag_main_out {
+  float depth [[depth(any)]];
+};
+
+fragment frag_main_out frag_main(float4 coord [[position]]) {
+  frag_main_out tint_out = {};
+  tint_out.depth = coord.x;
+  return tint_out;
+}
+
+)");
+}
+
 TEST_F(MslGeneratorImplTest,
-       Emit_Function_Called_By_EntryPoints_WithGlobals_And_Params) {
+       Emit_Function_Called_By_EntryPoints_WithLocationGlobals_And_Params) {
   ast::type::VoidType void_type;
   ast::type::F32Type f32;
 
@@ -318,6 +388,99 @@ fragment ep_1_out ep_1(ep_1_in tint_in [[stage_in]]) {
 )");
 }
 
+TEST_F(MslGeneratorImplTest,
+       Emit_Function_Called_By_EntryPoints_WithBuiltinGlobals_And_Params) {
+  ast::type::VoidType void_type;
+  ast::type::F32Type f32;
+  ast::type::VectorType vec4(&f32, 4);
+
+  auto coord_var =
+      std::make_unique<ast::DecoratedVariable>(std::make_unique<ast::Variable>(
+          "coord", ast::StorageClass::kInput, &vec4));
+
+  ast::VariableDecorationList decos;
+  decos.push_back(
+      std::make_unique<ast::BuiltinDecoration>(ast::Builtin::kFragCoord));
+  coord_var->set_decorations(std::move(decos));
+
+  auto depth_var =
+      std::make_unique<ast::DecoratedVariable>(std::make_unique<ast::Variable>(
+          "depth", ast::StorageClass::kOutput, &f32));
+  decos.push_back(
+      std::make_unique<ast::BuiltinDecoration>(ast::Builtin::kFragDepth));
+  depth_var->set_decorations(std::move(decos));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  td.RegisterVariableForTesting(coord_var.get());
+  td.RegisterVariableForTesting(depth_var.get());
+
+  mod.AddGlobalVariable(std::move(coord_var));
+  mod.AddGlobalVariable(std::move(depth_var));
+
+  ast::VariableList params;
+  params.push_back(std::make_unique<ast::Variable>(
+      "param", ast::StorageClass::kFunction, &f32));
+  auto sub_func =
+      std::make_unique<ast::Function>("sub_func", std::move(params), &f32);
+
+  ast::StatementList body;
+  body.push_back(std::make_unique<ast::AssignmentStatement>(
+      std::make_unique<ast::IdentifierExpression>("depth"),
+      std::make_unique<ast::MemberAccessorExpression>(
+          std::make_unique<ast::IdentifierExpression>("coord"),
+          std::make_unique<ast::IdentifierExpression>("x"))));
+  body.push_back(std::make_unique<ast::ReturnStatement>(
+      std::make_unique<ast::IdentifierExpression>("param")));
+  sub_func->set_body(std::move(body));
+
+  mod.AddFunction(std::move(sub_func));
+
+  auto func_1 = std::make_unique<ast::Function>("frag_1_main",
+                                                std::move(params), &void_type);
+
+  ast::ExpressionList expr;
+  expr.push_back(std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::FloatLiteral>(&f32, 1.0f)));
+  body.push_back(std::make_unique<ast::AssignmentStatement>(
+      std::make_unique<ast::IdentifierExpression>("depth"),
+      std::make_unique<ast::CallExpression>(
+          std::make_unique<ast::IdentifierExpression>("sub_func"),
+          std::move(expr))));
+  body.push_back(std::make_unique<ast::ReturnStatement>());
+  func_1->set_body(std::move(body));
+
+  mod.AddFunction(std::move(func_1));
+
+  auto ep1 = std::make_unique<ast::EntryPoint>(ast::PipelineStage::kFragment,
+                                               "ep_1", "frag_1_main");
+  mod.AddEntryPoint(std::move(ep1));
+
+  ASSERT_TRUE(td.Determine()) << td.error();
+
+  GeneratorImpl g;
+  ASSERT_TRUE(g.Generate(mod)) << g.error();
+  EXPECT_EQ(g.result(), R"(#include <metal_stdlib>
+
+struct ep_1_out {
+  float depth [[depth(any)]];
+};
+
+float sub_func_ep_1(thread ep_1_out& tint_out, thread float4& coord, float param) {
+  tint_out.depth = coord.x;
+  return param;
+}
+
+fragment ep_1_out ep_1(float4 coord [[position]]) {
+  ep_1_out tint_out = {};
+  tint_out.depth = sub_func_ep_1(tint_out, coord, 1.00000000f);
+  return tint_out;
+}
+
+)");
+}
+
 TEST_F(MslGeneratorImplTest, Emit_Function_Called_Two_EntryPoints_WithGlobals) {
   ast::type::VoidType void_type;
   ast::type::F32Type f32;

src/writer/msl/generator_impl_test.cc

@@ -74,6 +74,40 @@ TEST_F(MslGeneratorImplTest, NameConflictWith_InputStructName) {
   EXPECT_EQ(g.result(), "func_main_in_0");
 }
 
+struct MslBuiltinData {
+  ast::Builtin builtin;
+  const char* attribute_name;
+};
+inline std::ostream& operator<<(std::ostream& out, MslBuiltinData data) {
+  out << data.builtin;
+  return out;
+}
+using MslBuiltinConversionTest = testing::TestWithParam<MslBuiltinData>;
+TEST_P(MslBuiltinConversionTest, Emit) {
+  auto params = GetParam();
+
+  GeneratorImpl g;
+  EXPECT_EQ(g.builtin_to_attribute(params.builtin),
+            std::string(params.attribute_name));
+}
+INSTANTIATE_TEST_SUITE_P(
+    MslGeneratorImplTest,
+    MslBuiltinConversionTest,
+    testing::Values(MslBuiltinData{ast::Builtin::kPosition, "position"},
+                    MslBuiltinData{ast::Builtin::kVertexIdx, "vertex_id"},
+                    MslBuiltinData{ast::Builtin::kInstanceIdx, "instance_id"},
+                    MslBuiltinData{ast::Builtin::kFrontFacing, "front_facing"},
+                    MslBuiltinData{ast::Builtin::kFragCoord, "position"},
+                    MslBuiltinData{ast::Builtin::kFragDepth, "depth(any)"},
+                    MslBuiltinData{ast::Builtin::kNumWorkgroups, ""},
+                    MslBuiltinData{ast::Builtin::kWorkgroupSize, ""},
+                    MslBuiltinData{ast::Builtin::kLocalInvocationId,
+                                   "thread_position_in_threadgroup"},
+                    MslBuiltinData{ast::Builtin::kLocalInvocationIdx,
+                                   "thread_index_in_threadgroup"},
+                    MslBuiltinData{ast::Builtin::kGlobalInvocationId,
+                                   "thread_position_in_grid"}));
+
 }  // namespace
 }  // namespace msl
 }  // namespace writer