From 24d6bf3d96e4e4676449d10d7632e903fc9ae557 Mon Sep 17 00:00:00 2001
From: David Malcolm <dmalcolm@redhat.com>
Date: Thu, 3 Jul 2014 10:42:45 -0400
Subject: [PATCH 005/236] Introduce as_a_nullable

In many circumstances, is_a_helper <T>::test assumes that the pointer is
non-NULL, but sometimes you have a pointer of type T that can be NULL.

Earlier versions of this patch kit made numerous uses of the ternary
operator to handle nullable pointers e.g.:

  return insn ? as_a <rtx_insn *> (insn) : NULL;

but this was ugly.  Instead, introduce an as_a_nullable<T> variant that
adds a check for NULL, so the above can be written simply as:

  return as_a_nullable <rtx_insn *> (insn);

gcc/
	* is-a.h (template<T, U> as_a_nullable <U *p>) New function.
---
 gcc/is-a.h | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/gcc/is-a.h b/gcc/is-a.h
index a14e344..f50e62c 100644
--- a/gcc/is-a.h
+++ b/gcc/is-a.h
@@ -46,6 +46,14 @@ TYPE as_a <TYPE> (pointer)
 
       do_something_with (as_a <cgraph_node *> *ptr);
 
+TYPE as_a_nullable <TYPE> (pointer)
+
+    Like as_a <TYPE> (pointer), but where pointer could be NULL.  This
+    adds a check against NULL where the regular is_a_helper hook for TYPE
+    assumes non-NULL.
+
+      do_something_with (as_a_nullable <cgraph_node *> *ptr);
+
 TYPE dyn_cast <TYPE> (pointer)
 
     Converts pointer to TYPE if and only if "is_a <TYPE> pointer".  Otherwise,
@@ -185,6 +193,22 @@ as_a (U *p)
   return is_a_helper <T>::cast (p);
 }
 
+/* Similar to as_a<>, but where the pointer can be NULL, even if
+   is_a_helper<T> doesn't check for NULL.  */
+
+template <typename T, typename U>
+inline T
+as_a_nullable (U *p)
+{
+  if (p)
+    {
+      gcc_checking_assert (is_a <T> (p));
+      return is_a_helper <T>::cast (p);
+    }
+  else
+    return NULL;
+}
+
 /* A generic checked conversion from a base type U to a derived type T.  See
    the discussion above for when to use this function.  */
 
-- 
1.8.5.3