From 35a92f382e4abcd3c4e1ccd531f1ecfba128513d Mon Sep 17 00:00:00 2001
From: =?utf8?q?=EB=B0=95=EC=A2=85=ED=98=84/On-Device=20Lab=28SR=29/Staff?=
 =?utf8?q?=20Engineer/=EC=82=BC=EC=84=B1=EC=A0=84=EC=9E=90?=
 <jh1302.park@samsung.com>
Date: Fri, 14 Jun 2019 13:40:06 +0900
Subject: [PATCH] [loco] Canonical Node Visitor with default implementation
 (#3771)

* [loco] Canonical Node Visitor with default implementation

With this commit, users are able to implement a node visitor with their
own default implementation.

Signed-off-by: Jonghyun Park <jh1302.park@samsung.com>

* Fix a typo
---
 contrib/loco/include/loco/IR/CanonicalNode.h       |  2 +-
 contrib/loco/include/loco/IR/CanonicalNodeImpl.h   |  2 +-
 .../include/loco/IR/CanonicalNodeVisitor.forward.h |  2 +-
 .../loco/include/loco/IR/CanonicalNodeVisitor.h    | 43 +++++++++++++++++++---
 contrib/loco/src/IR/CanonicalNode.test.cpp         | 21 +++++++++++
 5 files changed, 62 insertions(+), 8 deletions(-)

diff --git a/contrib/loco/include/loco/IR/CanonicalNode.h b/contrib/loco/include/loco/IR/CanonicalNode.h
index d15855f..52239aa 100644
--- a/contrib/loco/include/loco/IR/CanonicalNode.h
+++ b/contrib/loco/include/loco/IR/CanonicalNode.h
@@ -32,7 +32,7 @@ struct CanonicalNode : public Node
   Dialect *dialect(void) const final;
   virtual CanonicalOpcode opcode(void) const = 0;
 
-  template <typename T> T accept(CanonicalNodeVisitor<T> *);
+  template <typename T> T accept(CanonicalNodeVisitorBase<T> *);
 };
 
 template <CanonicalOpcode Code> struct CanonicalNodeImpl : public CanonicalNode
diff --git a/contrib/loco/include/loco/IR/CanonicalNodeImpl.h b/contrib/loco/include/loco/IR/CanonicalNodeImpl.h
index 351276d..ed2f70a 100644
--- a/contrib/loco/include/loco/IR/CanonicalNodeImpl.h
+++ b/contrib/loco/include/loco/IR/CanonicalNodeImpl.h
@@ -25,7 +25,7 @@
 namespace loco
 {
 
-template <typename T> T CanonicalNode::accept(CanonicalNodeVisitor<T> *v)
+template <typename T> T CanonicalNode::accept(CanonicalNodeVisitorBase<T> *v)
 {
   switch (this->opcode())
   {
diff --git a/contrib/loco/include/loco/IR/CanonicalNodeVisitor.forward.h b/contrib/loco/include/loco/IR/CanonicalNodeVisitor.forward.h
index ba8da87..50bb11f 100644
--- a/contrib/loco/include/loco/IR/CanonicalNodeVisitor.forward.h
+++ b/contrib/loco/include/loco/IR/CanonicalNodeVisitor.forward.h
@@ -21,7 +21,7 @@ namespace loco
 {
 
 // NOTE This forward declaration SHOULD BE aligned with Node delcaration in "CanonicalNodeVisitor.h"
-template <typename T> struct CanonicalNodeVisitor;
+template <typename T> struct CanonicalNodeVisitorBase;
 
 } // namespace loco
 
diff --git a/contrib/loco/include/loco/IR/CanonicalNodeVisitor.h b/contrib/loco/include/loco/IR/CanonicalNodeVisitor.h
index 43e40c1..727b73f 100644
--- a/contrib/loco/include/loco/IR/CanonicalNodeVisitor.h
+++ b/contrib/loco/include/loco/IR/CanonicalNodeVisitor.h
@@ -24,8 +24,30 @@
 namespace loco
 {
 
+struct ThrowNotImplemented
+{
+  /**
+   * GCC rejects the following implementation of "CanonicalNodeVisitorImpl::visit":
+   *
+   * virtual T visit(const CLASS *)
+   * {
+   *   Fallback f;
+   *   return f.call<T>();
+   * }
+   *
+   * Let us pass "nullptr" of T * type (which serves as a type tag) as a workaround.
+   *
+   * TODO Remove this workaround if possible
+   */
+  template <typename T> T call(const T *) const
+  {
+    // Throw NYI exception
+    throw std::runtime_error{"Not implemented, yet"};
+  }
+};
+
 /**
- * DO NOT use this class. Use CanonicalNodeVisitor instead.
+ * DO NOT use this class. Use CanonicalNodeVisitor or CanonicalNodeVisitorImpl instead.
  */
 template <typename T> struct CanonicalNodeVisitorBase
 {
@@ -36,16 +58,27 @@ template <typename T> struct CanonicalNodeVisitorBase
 #undef CANONICAL_NODE
 };
 
-template <typename T> struct CanonicalNodeVisitor : public CanonicalNodeVisitorBase<T>
+template <typename T, typename Fallback>
+struct CanonicalNodeVisitorImpl : public CanonicalNodeVisitorBase<T>
 {
-  virtual ~CanonicalNodeVisitor() = default;
+  virtual ~CanonicalNodeVisitorImpl() = default;
 
-#define CANONICAL_NODE(OPCODE, CLASS) \
-  virtual T visit(const CLASS *) { throw std::runtime_error{"NYI"}; }
+#define CANONICAL_NODE(OPCODE, CLASS)               \
+  virtual T visit(const CLASS *)                    \
+  {                                                 \
+    Fallback f;                                     \
+    return f.call(static_cast<const T *>(nullptr)); \
+  }
 #include "CanonicalNodes.lst"
 #undef CANONICAL_NODE
 };
 
+template <typename T>
+struct CanonicalNodeVisitor : public CanonicalNodeVisitorImpl<T, ThrowNotImplemented>
+{
+  virtual ~CanonicalNodeVisitor() = default;
+};
+
 } // namespace loco
 
 #endif // __LOCO_IR_CANONICAL_NODE_VISITOR_H__
diff --git a/contrib/loco/src/IR/CanonicalNode.test.cpp b/contrib/loco/src/IR/CanonicalNode.test.cpp
index 9f4245f..6a6ab39 100644
--- a/contrib/loco/src/IR/CanonicalNode.test.cpp
+++ b/contrib/loco/src/IR/CanonicalNode.test.cpp
@@ -19,6 +19,27 @@
 
 #include <gtest/gtest.h>
 
+TEST(CanonicalNodeTest, visitor_with_user_default_impl)
+{
+  struct MyFallback
+  {
+    uint32_t call(const uint32_t *) const { return 256; }
+  };
+
+  struct MyVisitor final : public loco::CanonicalNodeVisitorImpl<uint32_t, MyFallback>
+  {
+    uint32_t visit(const loco::Forward *) final { return 128; }
+  };
+
+  loco::Forward forward;
+  loco::ConstGen constgen;
+
+  MyVisitor v;
+
+  ASSERT_EQ(forward.accept(&v), 128);
+  ASSERT_EQ(constgen.accept(&v), 256);
+}
+
 TEST(CanonicalNodeTest, visitor)
 {
   struct CountingVisitor final : public loco::CanonicalNodeVisitor<uint32_t>
-- 
2.7.4