[PATCH] RISC-V: Implement full-featured iterator for riscv_subset_list [NFC]

[Kito Cheng]

This commit implements a full-featured iterator for the
riscv_subset_list, that it able to use range-based-for-loop.

That could simplfy the code in the future, and make it more readable,
also more compatible with standard C++ containers.

gcc/ChangeLog:

        * config/riscv/riscv-c.cc (riscv_cpu_cpp_builtins): Use
        range-based-for-loop.
        * config/riscv/riscv-subset.h (riscv_subset_list::iterator):
        New.
        (riscv_subset_list::const_iterator): New.
---
 gcc/config/riscv/riscv-c.cc     | 18 ++++------
 gcc/config/riscv/riscv-subset.h | 62 +++++++++++++++++++++++++++++++--
 2 files changed, 66 insertions(+), 14 deletions(-)

diff --git a/gcc/config/riscv/riscv-c.cc b/gcc/config/riscv/riscv-c.cc
index 1ff1968f6d8..d2c0af35955 100644
--- a/gcc/config/riscv/riscv-c.cc
+++ b/gcc/config/riscv/riscv-c.cc
@@ -239,26 +239,22 @@ riscv_cpu_cpp_builtins (cpp_reader *pfile)
   size_t max_ext_len = 0;
 
   /* Figure out the max length of extension name for reserving buffer.   */
-  for (const riscv_subset_t *subset = subset_list->begin ();
-       subset != subset_list->end ();
-       subset = subset->next)
-    max_ext_len = MAX (max_ext_len, subset->name.length ());
+  for (auto &subset : *subset_list)
+    max_ext_len = MAX (max_ext_len, subset.name.length ());
 
   char *buf = (char *)alloca (max_ext_len + 10 /* For __riscv_ and '\0'.  */);
 
-  for (const riscv_subset_t *subset = subset_list->begin ();
-       subset != subset_list->end ();
-       subset = subset->next)
+  for (auto &subset : *subset_list)
     {
-      int version_value = riscv_ext_version_value (subset->major_version,
-                                                  subset->minor_version);
+      int version_value = riscv_ext_version_value (subset.major_version,
+                                                  subset.minor_version);
       /* Special rule for zicsr and zifencei, it's used for ISA spec 2.2 or
         earlier.  */
-      if ((subset->name == "zicsr" || subset->name == "zifencei")
+      if ((subset.name == "zicsr" || subset.name == "zifencei")
          && version_value == 0)
        version_value = riscv_ext_version_value (2, 0);
 
-      sprintf (buf, "__riscv_%s", subset->name.c_str ());
+      sprintf (buf, "__riscv_%s", subset.name.c_str ());
       builtin_define_with_int_value (buf, version_value);
     }
 }
diff --git a/gcc/config/riscv/riscv-subset.h b/gcc/config/riscv/riscv-subset.h
index c5d9fab4de9..a35537d7754 100644
--- a/gcc/config/riscv/riscv-subset.h
+++ b/gcc/config/riscv/riscv-subset.h
@@ -109,9 +109,6 @@ public:
   static riscv_subset_list *parse (const char *, location_t);
   const char *parse_single_ext (const char *, bool exact_single_p = true);
 
-  const riscv_subset_t *begin () const {return m_head;};
-  const riscv_subset_t *end () const {return NULL;};
-
   int match_score (riscv_subset_list *) const;
 
   void set_loc (location_t);
@@ -119,6 +116,65 @@ public:
   void set_allow_adding_dup (bool v) { m_allow_adding_dup = v; }
 
   void finalize ();
+
+  class iterator
+  {
+  public:
+    explicit iterator(riscv_subset_t *node) : m_node(node) {}
+
+    riscv_subset_t &operator*() const { return *m_node; }
+    riscv_subset_t *operator->() const { return m_node; }
+
+    iterator &operator++()
+    {
+      if (m_node)
+       m_node = m_node->next;
+      return *this;
+    }
+
+    bool operator!=(const iterator &other) const
+    {
+      return m_node != other.m_node;
+    }
+
+    bool operator==(const iterator &other) const
+    {
+      return m_node == other.m_node;
+    }
+
+  private:
+    riscv_subset_t *m_node;
+  };
+
+  iterator begin() { return iterator(m_head); }
+  iterator end()   { return iterator(nullptr); }
+
+  class const_iterator
+  {
+  public:
+    explicit const_iterator(const riscv_subset_t *node) : m_node(node) {}
+
+    const riscv_subset_t &operator*() const { return *m_node; }
+    const riscv_subset_t *operator->() const { return m_node; }
+
+    const_iterator &operator++()
+    {
+      if (m_node)
+       m_node = m_node->next;
+      return *this;
+    }
+
+    bool operator!=(const const_iterator &other) const
+    {
+      return m_node != other.m_node;
+    }
+
+  private:
+    const riscv_subset_t *m_node;
+  };
+
+  const_iterator begin() const { return const_iterator(m_head); }
+  const_iterator end() const   { return const_iterator(nullptr); }
 };
 
 extern const riscv_subset_list *riscv_cmdline_subset_list (void);
-- 
2.34.1