[hlsl-writer] Add AsExpression to the HLSL backend.

This CL adds as casts to the HLSL backend.

Bug: tint:7
Change-Id: I599527d665a3ec1ab6cf80b4f550f7aee8fdf294
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25843
Reviewed-by: David Neto <dneto@google.com>

BUILD.gn

@@ -1043,6 +1043,7 @@ source_set("tint_unittests_hlsl_writer_src") {
   sources = [
     "src/writer/hlsl/generator_impl_alias_type_test.cc",
     "src/writer/hlsl/generator_impl_array_accessor_test.cc",
+    "src/writer/hlsl/generator_impl_as_test.cc",
     "src/writer/hlsl/generator_impl_assign_test.cc",
     "src/writer/hlsl/generator_impl_binary_test.cc",
     "src/writer/hlsl/generator_impl_block_test.cc",

src/CMakeLists.txt

@@ -551,6 +551,7 @@ if (${TINT_BUILD_HLSL_WRITER})
   list(APPEND TINT_TEST_SRCS
     writer/hlsl/generator_impl_alias_type_test.cc
     writer/hlsl/generator_impl_array_accessor_test.cc
+    writer/hlsl/generator_impl_as_test.cc
     writer/hlsl/generator_impl_assign_test.cc
     writer/hlsl/generator_impl_binary_test.cc
     writer/hlsl/generator_impl_block_test.cc

src/writer/hlsl/generator_impl.cc

@@ -15,6 +15,7 @@
 #include "src/writer/hlsl/generator_impl.h"
 
 #include "src/ast/array_accessor_expression.h"
+#include "src/ast/as_expression.h"
 #include "src/ast/assignment_statement.h"
 #include "src/ast/binary_expression.h"
 #include "src/ast/bool_literal.h"
@@ -117,6 +118,25 @@ bool GeneratorImpl::EmitArrayAccessor(ast::ArrayAccessorExpression* expr) {
   return true;
 }
 
+bool GeneratorImpl::EmitAs(ast::AsExpression* expr) {
+  if (!expr->type()->IsF32() && !expr->type()->IsI32() &&
+      !expr->type()->IsU32()) {
+    error_ = "Unable to do as cast to type " + expr->type()->type_name();
+    return false;
+  }
+
+  out_ << "as";
+  if (!EmitType(expr->type(), "")) {
+    return false;
+  }
+  out_ << "(";
+  if (!EmitExpression(expr->expr())) {
+    return false;
+  }
+  out_ << ")";
+  return true;
+}
+
 bool GeneratorImpl::EmitAssign(ast::AssignmentStatement* stmt) {
   make_indent();
 
@@ -368,6 +388,9 @@ bool GeneratorImpl::EmitDiscard(ast::DiscardStatement*) {
 }
 
 bool GeneratorImpl::EmitExpression(ast::Expression* expr) {
+  if (expr->IsAs()) {
+    return EmitAs(expr->AsAs());
+  }
   if (expr->IsArrayAccessor()) {
     return EmitArrayAccessor(expr->AsArrayAccessor());
   }

src/writer/hlsl/generator_impl.h

@@ -46,6 +46,10 @@ class GeneratorImpl : public TextGenerator {
   /// @param expr the expression to emit
   /// @returns true if the array accessor was emitted
   bool EmitArrayAccessor(ast::ArrayAccessorExpression* expr);
+  /// Handles generating an as expression
+  /// @param expr the as expression
+  /// @returns true if the as was emitted
+  bool EmitAs(ast::AsExpression* expr);
   /// Handles an assignment statement
   /// @param stmt the statement to emit
   /// @returns true if the statement was emitted successfully

src/writer/hlsl/generator_impl_as_test.cc

@@ -0,0 +1,69 @@
+// 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/as_expression.h"
+#include "src/ast/identifier_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/u32_type.h"
+#include "src/writer/hlsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace hlsl {
+namespace {
+
+using HlslGeneratorImplTest = testing::Test;
+
+TEST_F(HlslGeneratorImplTest, EmitExpression_As_Float) {
+  ast::type::F32Type f32;
+  auto id = std::make_unique<ast::IdentifierExpression>("id");
+  ast::AsExpression as(&f32, std::move(id));
+
+  ast::Module m;
+  GeneratorImpl g(&m);
+  ASSERT_TRUE(g.EmitExpression(&as)) << g.error();
+  EXPECT_EQ(g.result(), "asfloat(id)");
+}
+
+TEST_F(HlslGeneratorImplTest, EmitExpression_As_Int) {
+  ast::type::I32Type i32;
+  auto id = std::make_unique<ast::IdentifierExpression>("id");
+  ast::AsExpression as(&i32, std::move(id));
+
+  ast::Module m;
+  GeneratorImpl g(&m);
+  ASSERT_TRUE(g.EmitExpression(&as)) << g.error();
+  EXPECT_EQ(g.result(), "asint(id)");
+}
+
+TEST_F(HlslGeneratorImplTest, EmitExpression_As_Uint) {
+  ast::type::U32Type u32;
+  auto id = std::make_unique<ast::IdentifierExpression>("id");
+  ast::AsExpression as(&u32, std::move(id));
+
+  ast::Module m;
+  GeneratorImpl g(&m);
+  ASSERT_TRUE(g.EmitExpression(&as)) << g.error();
+  EXPECT_EQ(g.result(), "asuint(id)");
+}
+
+}  // namespace
+}  // namespace hlsl
+}  // namespace writer
+}  // namespace tint