[msl-writer] Only emit in/out structs if function call requires.

This CL updates the EmitCall method to only ouptut the input and output
struct name if there are in/out variables used in the function.

Bug: tint:107
Change-Id: Ic0c7722c8796c2f9baa3515cb46be0568f9e1ac3
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25400
Reviewed-by: David Neto <dneto@google.com>

src/writer/msl/generator_impl.cc

@@ -420,23 +420,6 @@ bool GeneratorImpl::EmitCall(ast::CallExpression* expr) {
     if (it != ep_func_name_remapped_.end()) {
       name = it->second;
     }
-    out_ << name << "(";
-
-    bool first = true;
-    auto var_name = current_ep_var_name(VarType::kIn);
-    if (!var_name.empty()) {
-      out_ << var_name;
-      first = false;
-    }
-
-    var_name = current_ep_var_name(VarType::kOut);
-    if (!var_name.empty()) {
-      if (!first) {
-        out_ << ", ";
-      }
-      first = false;
-      out_ << var_name;
-    }
 
     auto* func = module_->FindFunctionByName(ident->name());
     if (func == nullptr) {
@@ -444,6 +427,27 @@ bool GeneratorImpl::EmitCall(ast::CallExpression* expr) {
       return false;
     }
 
+    out_ << name << "(";
+
+    bool first = true;
+    if (has_referenced_in_var_needing_struct(func)) {
+      auto var_name = current_ep_var_name(VarType::kIn);
+      if (!var_name.empty()) {
+        out_ << var_name;
+        first = false;
+      }
+    }
+    if (has_referenced_out_var_needing_struct(func)) {
+      auto var_name = current_ep_var_name(VarType::kOut);
+      if (!var_name.empty()) {
+        if (!first) {
+          out_ << ", ";
+        }
+        first = false;
+        out_ << var_name;
+      }
+    }
+
     for (const auto& data : func->referenced_builtin_variables()) {
       auto* var = data.first;
       if (var->storage_class() != ast::StorageClass::kInput) {
@@ -945,11 +949,20 @@ void GeneratorImpl::EmitStage(ast::PipelineStage stage) {
   return;
 }
 
-bool GeneratorImpl::has_referenced_var_needing_struct(ast::Function* func) {
+bool GeneratorImpl::has_referenced_in_var_needing_struct(ast::Function* func) {
   for (auto data : func->referenced_location_variables()) {
     auto* var = data.first;
-    if (var->storage_class() == ast::StorageClass::kInput ||
-        var->storage_class() == ast::StorageClass::kOutput) {
+    if (var->storage_class() == ast::StorageClass::kInput) {
+      return true;
+    }
+  }
+  return false;
+}
+
+bool GeneratorImpl::has_referenced_out_var_needing_struct(ast::Function* func) {
+  for (auto data : func->referenced_location_variables()) {
+    auto* var = data.first;
+    if (var->storage_class() == ast::StorageClass::kOutput) {
       return true;
     }
   }
@@ -960,10 +973,14 @@ bool GeneratorImpl::has_referenced_var_needing_struct(ast::Function* func) {
       return true;
     }
   }
-
   return false;
 }
 
+bool GeneratorImpl::has_referenced_var_needing_struct(ast::Function* func) {
+  return has_referenced_in_var_needing_struct(func) ||
+         has_referenced_out_var_needing_struct(func);
+}
+
 bool GeneratorImpl::EmitFunction(ast::Function* func) {
   make_indent();
 

src/writer/msl/generator_impl.h

@@ -207,6 +207,14 @@ class GeneratorImpl : public TextGenerator {
   /// @returns true if the zero value was successfully emitted.
   bool EmitZeroValue(ast::type::Type* type);
 
+  /// Determines if the function needs the input struct passed to it.
+  /// @param func the function to check
+  /// @returns true if there are input struct variables used in the function
+  bool has_referenced_in_var_needing_struct(ast::Function* func);
+  /// Determines if the function needs the output struct passed to it.
+  /// @param func the function to check
+  /// @returns true if there are output struct variables used in the function
+  bool has_referenced_out_var_needing_struct(ast::Function* func);
   /// Determines if any used module variable requires an input or output struct.
   /// @param func the function to check
   /// @returns true if an input or output struct is required.

src/writer/msl/generator_impl_function_test.cc

@@ -502,6 +502,84 @@ fragment ep_1_out ep_1(ep_1_in tint_in [[stage_in]]) {
 )");
 }
 
+TEST_F(MslGeneratorImplTest,
+       Emit_Function_Called_By_EntryPoints_NoUsedGlobals) {
+  ast::type::VoidType void_type;
+  ast::type::F32Type f32;
+  ast::type::VectorType vec4(&f32, 4);
+
+  auto depth_var =
+      std::make_unique<ast::DecoratedVariable>(std::make_unique<ast::Variable>(
+          "depth", ast::StorageClass::kOutput, &f32));
+
+  ast::VariableDecorationList decos;
+  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(depth_var.get());
+
+  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::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(&mod);
+  ASSERT_TRUE(g.Generate()) << g.error();
+  EXPECT_EQ(g.result(), R"(#include <metal_stdlib>
+
+struct ep_1_out {
+  float depth [[depth(any)]];
+};
+
+float sub_func(float param) {
+  return param;
+}
+
+fragment ep_1_out ep_1() {
+  ep_1_out tint_out = {};
+  tint_out.depth = sub_func(1.00000000f);
+  return tint_out;
+}
+
+)");
+}
+
 TEST_F(MslGeneratorImplTest,
        Emit_Function_Called_By_EntryPoints_WithBuiltinGlobals_And_Params) {
   ast::type::VoidType void_type;