Emit loop statement.

This CL emits the loop statement from the WGSL generator.

Bug: tint:4
Change-Id: I45be066ed306a71df053f7e61e6201a10a3d1056
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/17283
Reviewed-by: David Neto <dneto@google.com>

src/CMakeLists.txt

@@ -419,6 +419,7 @@ if(${TINT_BUILD_WGSL_WRITER})
     writer/wgsl/generator_impl_import_test.cc
     writer/wgsl/generator_impl_initializer_test.cc
     writer/wgsl/generator_impl_kill_test.cc
+    writer/wgsl/generator_impl_loop_test.cc
     writer/wgsl/generator_impl_member_accessor_test.cc
     writer/wgsl/generator_impl_nop_test.cc
     writer/wgsl/generator_impl_regardless_test.cc

src/ast/loop_statement.h

@@ -62,6 +62,8 @@ class LoopStatement : public Statement {
   const std::vector<std::unique_ptr<Statement>>& continuing() const {
     return continuing_;
   }
+  /// @returns true if there are continuing statements in the loop
+  bool has_continuing() const { return !continuing_.empty(); }
 
   /// @returns true if this is a loop statement
   bool IsLoop() const override { return true; }

src/ast/loop_statement_test.cc

@@ -60,6 +60,25 @@ TEST_F(LoopStatementTest, IsLoop) {
   EXPECT_TRUE(l.IsLoop());
 }
 
+TEST_F(LoopStatementTest, HasContinuing_WithoutContinuing) {
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<KillStatement>());
+
+  LoopStatement l(std::move(body), {});
+  EXPECT_FALSE(l.has_continuing());
+}
+
+TEST_F(LoopStatementTest, HasContinuing_WithContinuing) {
+  std::vector<std::unique_ptr<Statement>> body;
+  body.push_back(std::make_unique<KillStatement>());
+
+  std::vector<std::unique_ptr<Statement>> continuing;
+  continuing.push_back(std::make_unique<NopStatement>());
+
+  LoopStatement l(std::move(body), std::move(continuing));
+  EXPECT_TRUE(l.has_continuing());
+}
+
 TEST_F(LoopStatementTest, IsValid) {
   std::vector<std::unique_ptr<Statement>> body;
   body.push_back(std::make_unique<KillStatement>());

src/writer/wgsl/generator_impl.cc

@@ -35,6 +35,7 @@
 #include "src/ast/initializer_expression.h"
 #include "src/ast/int_literal.h"
 #include "src/ast/location_decoration.h"
+#include "src/ast/loop_statement.h"
 #include "src/ast/member_accessor_expression.h"
 #include "src/ast/regardless_statement.h"
 #include "src/ast/relational_expression.h"
@@ -671,6 +672,9 @@ bool GeneratorImpl::EmitStatement(ast::Statement* stmt) {
   if (stmt->IsKill()) {
     return EmitKill(stmt->AsKill());
   }
+  if (stmt->IsLoop()) {
+    return EmitLoop(stmt->AsLoop());
+  }
   if (stmt->IsNop()) {
     return EmitNop(stmt->AsNop());
   }
@@ -803,6 +807,43 @@ bool GeneratorImpl::EmitKill(ast::KillStatement*) {
   return true;
 }
 
+bool GeneratorImpl::EmitLoop(ast::LoopStatement* stmt) {
+  make_indent();
+
+  out_ << "loop {" << std::endl;
+  increment_indent();
+
+  for (const auto& s : stmt->body()) {
+    if (!EmitStatement(s.get())) {
+      return false;
+    }
+  }
+
+  if (stmt->has_continuing()) {
+    out_ << std::endl;
+
+    make_indent();
+    out_ << "continuing {" << std::endl;
+
+    increment_indent();
+    for (const auto& s : stmt->continuing()) {
+      if (!EmitStatement(s.get())) {
+        return false;
+      }
+    }
+
+    decrement_indent();
+    make_indent();
+    out_ << "}" << std::endl;
+  }
+
+  decrement_indent();
+  make_indent();
+  out_ << "}" << std::endl;
+
+  return true;
+}
+
 bool GeneratorImpl::EmitNop(ast::NopStatement*) {
   make_indent();
   out_ << "nop;" << std::endl;

src/writer/wgsl/generator_impl.h

@@ -138,6 +138,10 @@ class GeneratorImpl {
   /// @param lit the literal to emit
   /// @returns true if the literal was successfully emitted
   bool EmitLiteral(ast::Literal* lit);
+  /// Handles a loop statement
+  /// @param stmt the statement to emit
+  /// @returns true if the statement was emtited
+  bool EmitLoop(ast::LoopStatement* stmt);
   /// Handles a member accessor expression
   /// @param expr the member accessor expression
   /// @returns true if the member accessor was emitted

src/writer/wgsl/generator_impl_loop_test.cc

@@ -0,0 +1,73 @@
+// 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 <vector>
+
+#include "gtest/gtest.h"
+#include "src/ast/kill_statement.h"
+#include "src/ast/loop_statement.h"
+#include "src/ast/nop_statement.h"
+#include "src/writer/wgsl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace wgsl {
+namespace {
+
+using GeneratorImplTest = testing::Test;
+
+TEST_F(GeneratorImplTest, Emit_Loop) {
+  std::vector<std::unique_ptr<ast::Statement>> body;
+  body.push_back(std::make_unique<ast::KillStatement>());
+
+  ast::LoopStatement l(std::move(body), {});
+
+  GeneratorImpl g;
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&l)) << g.error();
+  EXPECT_EQ(g.result(), R"(  loop {
+    kill;
+  }
+)");
+}
+
+TEST_F(GeneratorImplTest, Emit_LoopWithContinuing) {
+  std::vector<std::unique_ptr<ast::Statement>> body;
+  body.push_back(std::make_unique<ast::KillStatement>());
+
+  std::vector<std::unique_ptr<ast::Statement>> continuing;
+  continuing.push_back(std::make_unique<ast::NopStatement>());
+
+  ast::LoopStatement l(std::move(body), std::move(continuing));
+
+  GeneratorImpl g;
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&l)) << g.error();
+  EXPECT_EQ(g.result(), R"(  loop {
+    kill;
+
+    continuing {
+      nop;
+    }
+  }
+)");
+}
+
+}  // namespace
+}  // namespace wgsl
+}  // namespace writer
+}  // namespace tint