spirv-writer: Generate load for return value, when needed

spirv-writer: treat function parameter as const

Bug: tint:274
Change-Id: Iba4d90ea10a70ce1f551b7b8da6efcc01fe97412
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/30924
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: dan sinclair <dsinclair@chromium.org>

src/writer/spirv/builder.cc

@@ -2151,6 +2151,7 @@ bool Builder::GenerateReturnStatement(ast::ReturnStatement* stmt) {
     if (val_id == 0) {
       return false;
     }
+    val_id = GenerateLoadIfNeeded(stmt->value()->result_type(), val_id);
     push_function_inst(spv::Op::OpReturnValue, {Operand::Int(val_id)});
   } else {
     push_function_inst(spv::Op::OpReturn, {});

src/writer/spirv/builder_function_test.cc

@@ -24,6 +24,8 @@
 #include "src/ast/type/i32_type.h"
 #include "src/ast/type/void_type.h"
 #include "src/ast/variable.h"
+#include "src/context.h"
+#include "src/type_determiner.h"
 #include "src/writer/spirv/builder.h"
 #include "src/writer/spirv/spv_dump.h"
 
@@ -60,10 +62,14 @@ TEST_F(BuilderTest, Function_WithParams) {
   ast::type::I32Type i32;
 
   ast::VariableList params;
-  params.push_back(
-      std::make_unique<ast::Variable>("a", ast::StorageClass::kFunction, &f32));
-  params.push_back(
-      std::make_unique<ast::Variable>("b", ast::StorageClass::kFunction, &i32));
+  auto var_a =
+      std::make_unique<ast::Variable>("a", ast::StorageClass::kFunction, &f32);
+  var_a->set_is_const(true);
+  params.push_back(std::move(var_a));
+  auto var_b =
+      std::make_unique<ast::Variable>("b", ast::StorageClass::kFunction, &i32);
+  var_b->set_is_const(true);
+  params.push_back(std::move(var_b));
 
   ast::Function func("a_func", std::move(params), &f32);
 
@@ -72,7 +78,13 @@ TEST_F(BuilderTest, Function_WithParams) {
       std::make_unique<ast::IdentifierExpression>("a")));
   func.set_body(std::move(body));
 
+  Context ctx;
   ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  td.RegisterVariableForTesting(func.params()[0].get());
+  td.RegisterVariableForTesting(func.params()[1].get());
+  EXPECT_TRUE(td.DetermineFunction(&func));
+
   Builder b(&mod);
   ASSERT_TRUE(b.GenerateFunction(&func));
   EXPECT_EQ(DumpBuilder(b), R"(OpName %4 "a_func"
@@ -87,7 +99,7 @@ OpName %6 "b"
 %7 = OpLabel
 OpReturnValue %5
 OpFunctionEnd
-)");
+)") << DumpBuilder(b);
 }
 
 TEST_F(BuilderTest, Function_WithBody) {

src/writer/spirv/builder_return_test.cc

@@ -16,6 +16,7 @@
 
 #include "gtest/gtest.h"
 #include "src/ast/float_literal.h"
+#include "src/ast/identifier_expression.h"
 #include "src/ast/return_statement.h"
 #include "src/ast/scalar_constructor_expression.h"
 #include "src/ast/type/f32_type.h"
@@ -84,6 +85,39 @@ TEST_F(BuilderTest, Return_WithValue) {
 )");
 }
 
+TEST_F(BuilderTest, Return_WithValue_GeneratesLoad) {
+  ast::type::F32Type f32;
+
+  ast::Variable var("param", ast::StorageClass::kFunction, &f32);
+
+  ast::ReturnStatement ret(
+      std::make_unique<ast::IdentifierExpression>("param"));
+
+  Context ctx;
+  ast::Module mod;
+  TypeDeterminer td(&ctx, &mod);
+  td.RegisterVariableForTesting(&var);
+  EXPECT_TRUE(td.DetermineResultType(&ret)) << td.error();
+
+  Builder b(&mod);
+  b.push_function(Function{});
+  EXPECT_TRUE(b.GenerateFunctionVariable(&var)) << b.error();
+  EXPECT_TRUE(b.GenerateReturnStatement(&ret)) << b.error();
+  ASSERT_FALSE(b.has_error()) << b.error();
+
+  EXPECT_EQ(DumpInstructions(b.types()), R"(%3 = OpTypeFloat 32
+%2 = OpTypePointer Function %3
+%4 = OpConstantNull %3
+)");
+  EXPECT_EQ(DumpInstructions(b.functions()[0].variables()),
+            R"(%1 = OpVariable %2 Function %4
+)");
+  EXPECT_EQ(DumpInstructions(b.functions()[0].instructions()),
+            R"(%5 = OpLoad %3 %1
+OpReturnValue %5
+)");
+}
+
 }  // namespace
 }  // namespace spirv
 }  // namespace writer