[PATCH 3/4] Use tag dispatch regcache ctor in regcache_dup

[Yao Qi <qiyaoltc@gmail.com>]

This patch adds a tag dispatch ctor to create read-only regcache from
a write-through regcache, also this patch deletes copy ctor and
assignment operator.

gdb:

2017-04-27  Yao Qi  <yao.qi@linaro.org>
	    Pedro Alves  <palves@redhat.com>

	* regcache.c (regcache::regcache): New tag dispatch ctor.
	(do_cooked_read): Moved above.
	(regcache_dup): Use the tag dispatch ctor..
	* regcache.h (regcache): Declare ctor, delete copy ctor and
	assignment operator, remove friend regcache_dup.
---
 gdb/regcache.c | 30 ++++++++++++++++--------------
 gdb/regcache.h | 12 +++++++++---
 2 files changed, 25 insertions(+), 17 deletions(-)

diff --git a/gdb/regcache.c b/gdb/regcache.c
index 0be5fdb..882573c 100644
--- a/gdb/regcache.c
+++ b/gdb/regcache.c
@@ -209,6 +209,21 @@ regcache::regcache (gdbarch *gdbarch, address_space *aspace_,
   m_ptid = minus_one_ptid;
 }
 
+static enum register_status
+do_cooked_read (void *src, int regnum, gdb_byte *buf)
+{
+  struct regcache *regcache = (struct regcache *) src;
+
+  return regcache_cooked_read (regcache, regnum, buf);
+}
+
+regcache::regcache (readonly_t, const regcache &src)
+  : regcache (src.get_gdbarch (), src.aspace (), true)
+{
+  gdb_assert (!src.m_readonly_p);
+  save (do_cooked_read, (void *) &src);
+}
+
 gdbarch *
 regcache::get_gdbarch () const
 {
@@ -371,14 +386,6 @@ regcache::restore (struct regcache *src)
     }
 }
 
-static enum register_status
-do_cooked_read (void *src, int regnum, gdb_byte *buf)
-{
-  struct regcache *regcache = (struct regcache *) src;
-
-  return regcache_cooked_read (regcache, regnum, buf);
-}
-
 void
 regcache_cpy (struct regcache *dst, struct regcache *src)
 {
@@ -420,12 +427,7 @@ regcache::cpy_no_passthrough (struct regcache *src)
 struct regcache *
 regcache_dup (struct regcache *src)
 {
-  struct regcache *newbuf;
-
-  gdb_assert (!src->readonly_p);
-  newbuf = regcache_xmalloc (src->get_gdbarch (), get_regcache_aspace (src));
-  newbuf->save (do_cooked_read, src);
-  return newbuf;
+  return new regcache (regcache::readonly, *src);
 }
 
 enum register_status
diff --git a/gdb/regcache.h b/gdb/regcache.h
index 713fd41..92defdd 100644
--- a/gdb/regcache.h
+++ b/gdb/regcache.h
@@ -240,6 +240,15 @@ public:
     : regcache (gdbarch, aspace_, true)
   {}
 
+  struct readonly_t {};
+  static constexpr readonly_t readonly {};
+
+  /* Create a readonly regcache from a non-readonly regcache.  */
+  regcache (readonly_t, const regcache &src);
+
+  regcache (const regcache &) = delete;
+  void operator= (const regcache &) = delete;
+
   ~regcache ()
   {
     xfree (m_registers);
@@ -373,9 +382,6 @@ private:
 
   friend void
   regcache_cpy (struct regcache *dst, struct regcache *src);
-
-  friend struct regcache *
-  regcache_dup (struct regcache *src);
 };
 
 /* Copy/duplicate the contents of a register cache.  By default, the
-- 
1.9.1