[hlsl-writer] Add switch statement support

This CL adds emission of switch statements to the HLSL backend.

Bug: tint:7
Change-Id: Ie6f41031878a1f5a945f9310429d28fb0e4a98c8
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25223
Reviewed-by: David Neto <dneto@google.com>

BUILD.gn

@@ -1024,6 +1024,7 @@ source_set("tint_unittests_hlsl_writer_src") {
     "src/writer/hlsl/generator_impl_continue_test.cc",
     "src/writer/hlsl/generator_impl_identifier_test.cc",
     "src/writer/hlsl/generator_impl_return_test.cc",
+    "src/writer/hlsl/generator_impl_switch_test.cc",
     "src/writer/hlsl/generator_impl_test.cc",
     "src/writer/hlsl/generator_impl_unary_op_test.cc",
     "src/writer/hlsl/namer_test.cc",

src/CMakeLists.txt

@@ -548,6 +548,7 @@ if (${TINT_BUILD_HLSL_WRITER})
     writer/hlsl/generator_impl_continue_test.cc
     writer/hlsl/generator_impl_identifier_test.cc
     writer/hlsl/generator_impl_return_test.cc
+    writer/hlsl/generator_impl_switch_test.cc
     writer/hlsl/generator_impl_test.cc
     writer/hlsl/generator_impl_unary_op_test.cc
     writer/hlsl/namer_test.cc

src/writer/hlsl/generator_impl.cc

@@ -21,6 +21,7 @@
 #include "src/ast/identifier_expression.h"
 #include "src/ast/return_statement.h"
 #include "src/ast/sint_literal.h"
+#include "src/ast/switch_statement.h"
 #include "src/ast/uint_literal.h"
 #include "src/ast/unary_op_expression.h"
 
@@ -317,11 +318,38 @@ bool GeneratorImpl::EmitStatement(ast::Statement* stmt) {
   if (stmt->IsReturn()) {
     return EmitReturn(stmt->AsReturn());
   }
+  if (stmt->IsSwitch()) {
+    return EmitSwitch(stmt->AsSwitch());
+  }
 
   error_ = "unknown statement type: " + stmt->str();
   return false;
 }
 
+bool GeneratorImpl::EmitSwitch(ast::SwitchStatement* stmt) {
+  make_indent();
+
+  out_ << "switch(";
+  if (!EmitExpression(stmt->condition())) {
+    return false;
+  }
+  out_ << ") {" << std::endl;
+
+  increment_indent();
+
+  for (const auto& s : stmt->body()) {
+    if (!EmitCase(s.get())) {
+      return false;
+    }
+  }
+
+  decrement_indent();
+  make_indent();
+  out_ << "}" << std::endl;
+
+  return true;
+}
+
 bool GeneratorImpl::EmitUnaryOp(ast::UnaryOpExpression* expr) {
   switch (expr->op()) {
     case ast::UnaryOp::kNot:

src/writer/hlsl/generator_impl.h

@@ -72,6 +72,10 @@ class GeneratorImpl : public TextGenerator {
   /// @param stmt the statement to emit
   /// @returns true if the statement was emitted
   bool EmitStatement(ast::Statement* stmt);
+  /// Handles generating a switch statement
+  /// @param stmt the statement to emit
+  /// @returns true if the statement was emitted
+  bool EmitSwitch(ast::SwitchStatement* stmt);
   /// Handles a unary op expression
   /// @param expr the expression to emit
   /// @returns true if the expression was emitted

src/writer/hlsl/generator_impl_switch_test.cc

@@ -0,0 +1,76 @@
+// 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/break_statement.h"
+#include "src/ast/case_statement.h"
+#include "src/ast/identifier_expression.h"
+#include "src/ast/module.h"
+#include "src/ast/sint_literal.h"
+#include "src/ast/switch_statement.h"
+#include "src/ast/type/i32_type.h"
+#include "src/writer/hlsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace hlsl {
+namespace {
+
+using HlslGeneratorImplTest = testing::Test;
+
+TEST_F(HlslGeneratorImplTest, Emit_Switch) {
+  auto def = std::make_unique<ast::CaseStatement>();
+  ast::StatementList def_body;
+  def_body.push_back(std::make_unique<ast::BreakStatement>());
+  def->set_body(std::move(def_body));
+
+  ast::type::I32Type i32;
+  ast::CaseSelectorList case_val;
+  case_val.push_back(std::make_unique<ast::SintLiteral>(&i32, 5));
+
+  ast::StatementList case_body;
+  case_body.push_back(std::make_unique<ast::BreakStatement>());
+
+  auto case_stmt = std::make_unique<ast::CaseStatement>(std::move(case_val),
+                                                        std::move(case_body));
+
+  ast::CaseStatementList body;
+  body.push_back(std::move(case_stmt));
+  body.push_back(std::move(def));
+
+  auto cond = std::make_unique<ast::IdentifierExpression>("cond");
+  ast::SwitchStatement s(std::move(cond), std::move(body));
+
+  ast::Module m;
+  GeneratorImpl g(&m);
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&s)) << g.error();
+  EXPECT_EQ(g.result(), R"(  switch(cond) {
+    case 5: {
+      break;
+    }
+    default: {
+      break;
+    }
+  }
+)");
+}
+
+}  // namespace
+}  // namespace hlsl
+}  // namespace writer
+}  // namespace tint