Add type determination for return statement.

This CL adds the type determination code for the return statements.

Bug: tint:5
Change-Id: I0300fe0c66e7b8c25d1dc0ed22aef8cc469567be
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/18837
Reviewed-by: David Neto <dneto@google.com>

src/type_determiner.cc

@@ -22,6 +22,7 @@
 #include "src/ast/if_statement.h"
 #include "src/ast/loop_statement.h"
 #include "src/ast/regardless_statement.h"
+#include "src/ast/return_statement.h"
 #include "src/ast/scalar_constructor_expression.h"
 #include "src/ast/type_constructor_expression.h"
 
@@ -129,6 +130,10 @@ bool TypeDeterminer::DetermineResultType(ast::Statement* stmt) {
     return DetermineResultType(r->condition()) &&
            DetermineResultType(r->body());
   }
+  if (stmt->IsReturn()) {
+    auto r = stmt->AsReturn();
+    return DetermineResultType(r->value());
+  }
   if (stmt->IsNop()) {
     return true;
   }

src/type_determiner_test.cc

@@ -28,6 +28,7 @@
 #include "src/ast/int_literal.h"
 #include "src/ast/loop_statement.h"
 #include "src/ast/regardless_statement.h"
+#include "src/ast/return_statement.h"
 #include "src/ast/scalar_constructor_expression.h"
 #include "src/ast/type/f32_type.h"
 #include "src/ast/type/i32_type.h"
@@ -278,6 +279,20 @@ TEST_F(TypeDeterminerTest, Stmt_Regardless) {
   EXPECT_TRUE(rhs_ptr->result_type()->IsF32());
 }
 
+TEST_F(TypeDeterminerTest, Stmt_Return) {
+  ast::type::I32Type i32;
+
+  auto cond = std::make_unique<ast::ScalarConstructorExpression>(
+      std::make_unique<ast::IntLiteral>(&i32, 2));
+  auto cond_ptr = cond.get();
+
+  ast::ReturnStatement ret(std::move(cond));
+
+  EXPECT_TRUE(td()->DetermineResultType(&ret));
+  ASSERT_NE(cond_ptr->result_type(), nullptr);
+  EXPECT_TRUE(cond_ptr->result_type()->IsI32());
+}
+
 TEST_F(TypeDeterminerTest, Expr_Constructor_Scalar) {
   ast::type::F32Type f32;
   ast::ScalarConstructorExpression s(