From a9696b511fabac24a6acc7e22faea7d55f8c840f Mon Sep 17 00:00:00 2001
From: dan sinclair <dsinclair@google.com>
Date: Sat, 25 Jul 2020 14:32:54 +0000
Subject: [PATCH] [msl-writer] Emit DiscardStatement.

This CL adds the DiscardStatement to the MSL backend.

Bug: tint:164
Change-Id: I1e201d3b6a167690af7bb799e1c93e48232f4a0a
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/25602
Reviewed-by: David Neto <dneto@google.com>
---
 BUILD.gn                                      |  1 +
 src/CMakeLists.txt                            |  1 +
 src/writer/msl/generator_impl.cc              | 11 +++++
 src/writer/msl/generator_impl.h               |  4 ++
 src/writer/msl/generator_impl_discard_test.cc | 41 +++++++++++++++++++
 5 files changed, 58 insertions(+)
 create mode 100644 src/writer/msl/generator_impl_discard_test.cc

diff --git a/BUILD.gn b/BUILD.gn
index fa52285d71..c329fa01ba 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -994,6 +994,7 @@ source_set("tint_unittests_msl_writer_src") {
     "src/writer/msl/generator_impl_cast_test.cc",
     "src/writer/msl/generator_impl_constructor_test.cc",
     "src/writer/msl/generator_impl_continue_test.cc",
+    "src/writer/msl/generator_impl_discard_test.cc",
     "src/writer/msl/generator_impl_entry_point_test.cc",
     "src/writer/msl/generator_impl_function_test.cc",
     "src/writer/msl/generator_impl_identifier_test.cc",
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 4f35b61f7b..aa92225c00 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -525,6 +525,7 @@ if(${TINT_BUILD_MSL_WRITER})
     writer/msl/generator_impl_cast_test.cc
     writer/msl/generator_impl_constructor_test.cc
     writer/msl/generator_impl_continue_test.cc
+    writer/msl/generator_impl_discard_test.cc
     writer/msl/generator_impl_entry_point_test.cc
     writer/msl/generator_impl_function_test.cc
     writer/msl/generator_impl_identifier_test.cc
diff --git a/src/writer/msl/generator_impl.cc b/src/writer/msl/generator_impl.cc
index 4a4119ee9f..248a33936e 100644
--- a/src/writer/msl/generator_impl.cc
+++ b/src/writer/msl/generator_impl.cc
@@ -1389,6 +1389,14 @@ bool GeneratorImpl::EmitLoop(ast::LoopStatement* stmt) {
   return true;
 }
 
+bool GeneratorImpl::EmitDiscard(ast::DiscardStatement*) {
+  make_indent();
+  // TODO(dsinclair): Verify this is correct when the discard semantics are
+  // defined for WGSL (https://github.com/gpuweb/gpuweb/issues/361)
+  out_ << "discard_fragment();" << std::endl;
+  return true;
+}
+
 bool GeneratorImpl::EmitKill(ast::KillStatement*) {
   make_indent();
   // TODO(dsinclair): Verify this is correct when the kill semantics are defined
@@ -1509,6 +1517,9 @@ bool GeneratorImpl::EmitStatement(ast::Statement* stmt) {
   if (stmt->IsContinue()) {
     return EmitContinue(stmt->AsContinue());
   }
+  if (stmt->IsDiscard()) {
+    return EmitDiscard(stmt->AsDiscard());
+  }
   if (stmt->IsFallthrough()) {
     make_indent();
     out_ << "/* fallthrough */" << std::endl;
diff --git a/src/writer/msl/generator_impl.h b/src/writer/msl/generator_impl.h
index e2a0e3844b..5f5b31c1e1 100644
--- a/src/writer/msl/generator_impl.h
+++ b/src/writer/msl/generator_impl.h
@@ -97,6 +97,10 @@ class GeneratorImpl : public TextGenerator {
   /// @param stmt the statement to emit
   /// @returns true if the statement was emitted successfully
   bool EmitContinue(ast::ContinueStatement* stmt);
+  /// Handles generating a discard statement
+  /// @param stmt the discard statement
+  /// @returns true if the statement was successfully emitted
+  bool EmitDiscard(ast::DiscardStatement* stmt);
   /// Handles generating an else statement
   /// @param stmt the statement to emit
   /// @returns true if the statement was emitted
diff --git a/src/writer/msl/generator_impl_discard_test.cc b/src/writer/msl/generator_impl_discard_test.cc
new file mode 100644
index 0000000000..5d3ab30559
--- /dev/null
+++ b/src/writer/msl/generator_impl_discard_test.cc
@@ -0,0 +1,41 @@
+// 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 "gtest/gtest.h"
+#include "src/ast/discard_statement.h"
+#include "src/ast/module.h"
+#include "src/writer/msl/generator_impl.h"
+
+namespace tint {
+namespace writer {
+namespace msl {
+namespace {
+
+using MslGeneratorImplTest = testing::Test;
+
+TEST_F(MslGeneratorImplTest, Emit_Discard) {
+  ast::DiscardStatement stmt;
+
+  ast::Module m;
+  GeneratorImpl g(&m);
+  g.increment_indent();
+
+  ASSERT_TRUE(g.EmitStatement(&stmt)) << g.error();
+  EXPECT_EQ(g.result(), "  discard_fragment();\n");
+}
+
+}  // namespace
+}  // namespace msl
+}  // namespace writer
+}  // namespace tint