[hlsl-writer] Emit cast expressions.

This CL adds support for cast expressions to the HLSL backend.

Bug: tint:7
Change-Id: Ie7e180dc89abf137ab7d9b8790cc4206b3d5a672
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/26926
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Reviewed-by: David Neto <dneto@google.com>

BUILD.gn

@@ -1065,6 +1065,7 @@ source_set("tint_unittests_hlsl_writer_src") {
     "src/writer/hlsl/generator_impl_break_test.cc",
     "src/writer/hlsl/generator_impl_call_test.cc",
     "src/writer/hlsl/generator_impl_case_test.cc",
+    "src/writer/hlsl/generator_impl_cast_test.cc",
     "src/writer/hlsl/generator_impl_constructor_test.cc",
     "src/writer/hlsl/generator_impl_continue_test.cc",
     "src/writer/hlsl/generator_impl_discard_test.cc",

src/CMakeLists.txt

@@ -576,6 +576,7 @@ if (${TINT_BUILD_HLSL_WRITER})
     writer/hlsl/generator_impl_break_test.cc
     writer/hlsl/generator_impl_call_test.cc
     writer/hlsl/generator_impl_case_test.cc
+    writer/hlsl/generator_impl_cast_test.cc
     writer/hlsl/generator_impl_constructor_test.cc
     writer/hlsl/generator_impl_continue_test.cc
     writer/hlsl/generator_impl_discard_test.cc

src/writer/hlsl/generator_impl.cc

@@ -22,6 +22,7 @@
 #include "src/ast/call_expression.h"
 #include "src/ast/call_statement.h"
 #include "src/ast/case_statement.h"
+#include "src/ast/cast_expression.h"
 #include "src/ast/decorated_variable.h"
 #include "src/ast/else_statement.h"
 #include "src/ast/float_literal.h"
@@ -404,6 +405,19 @@ bool GeneratorImpl::EmitCall(ast::CallExpression* expr) {
   return true;
 }
 
+bool GeneratorImpl::EmitCast(ast::CastExpression* expr) {
+  if (!EmitType(expr->type(), "")) {
+    return false;
+  }
+
+  out_ << "(";
+  if (!EmitExpression(expr->expr())) {
+    return false;
+  }
+  out_ << ")";
+  return true;
+}
+
 bool GeneratorImpl::EmitCase(ast::CaseStatement* stmt) {
   make_indent();
 
@@ -525,6 +539,9 @@ bool GeneratorImpl::EmitExpression(ast::Expression* expr) {
   if (expr->IsCall()) {
     return EmitCall(expr->AsCall());
   }
+  if (expr->IsCast()) {
+    return EmitCast(expr->AsCast());
+  }
   if (expr->IsConstructor()) {
     return EmitConstructor(expr->AsConstructor());
   }

src/writer/hlsl/generator_impl.h

@@ -82,6 +82,10 @@ class GeneratorImpl : public TextGenerator {
   /// @param stmt the statement
   /// @returns true if the statment was emitted successfully
   bool EmitCase(ast::CaseStatement* stmt);
+  /// Handles generating a cast expression
+  /// @param expr the cast expression
+  /// @returns true if the cast was emitted
+  bool EmitCast(ast::CastExpression* expr);
   /// Handles generating constructor expressions
   /// @param expr the constructor expression
   /// @returns true if the expression was emitted

src/writer/hlsl/generator_impl_cast_test.cc

@@ -0,0 +1,59 @@
+// 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 <memory>
+
+#include "gtest/gtest.h"
+#include "src/ast/cast_expression.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/module.h"
+#include "src/ast/type/f32_type.h"
+#include "src/ast/type/vector_type.h"
+#include "src/writer/hlsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace hlsl {
+namespace {
+
+using HlslGeneratorImplTest = testing::Test;
+
+TEST_F(HlslGeneratorImplTest, EmitExpression_Cast_Scalar) {
+  ast::type::F32Type f32;
+  auto id = std::make_unique<ast::IdentifierExpression>("id");
+  ast::CastExpression cast(&f32, std::move(id));
+
+  ast::Module m;
+  GeneratorImpl g(&m);
+  ASSERT_TRUE(g.EmitExpression(&cast)) << g.error();
+  EXPECT_EQ(g.result(), "float(id)");
+}
+
+TEST_F(HlslGeneratorImplTest, EmitExpression_Cast_Vector) {
+  ast::type::F32Type f32;
+  ast::type::VectorType vec3(&f32, 3);
+
+  auto id = std::make_unique<ast::IdentifierExpression>("id");
+  ast::CastExpression cast(&vec3, std::move(id));
+
+  ast::Module m;
+  GeneratorImpl g(&m);
+  ASSERT_TRUE(g.EmitExpression(&cast)) << g.error();
+  EXPECT_EQ(g.result(), "vector<float, 3>(id)");
+}
+
+}  // namespace
+}  // namespace hlsl
+}  // namespace writer
+}  // namespace tint