Add TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID

        * gimple.c (check_loadstore): Return false when 0 is a valid address.
        * fold-const.c (const_unop) [ADDR_SPACE_CONVERT_EXPR]: Do not fold
        null when 0 is valid in the source address space.
        * target.def (TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID): New.
        * targhooks.c (default_addr_space_zero_address_valid): New.
        * targhooks.h (default_addr_space_zero_address_valid): Declare.
        * doc/tm.texi.in (TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID): Mark it.
        * doc/tm.texi: Rebuild.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@229999 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 10 insertions, 3 deletions

diff --git a/gcc/gimple.c b/gcc/gimple.c
index 4ce38dadf2f..706b126e5bb 100644
--- a/gcc/gimple.c
+++ b/gcc/gimple.c
@@ -37,6 +37,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "gimple-iterator.h"
 #include "gimple-walk.h"
 #include "gimplify.h"
+#include "target.h"
 
 
 /* All the tuples have their operand vector (if present) at the very bottom
@@ -2624,9 +2625,15 @@ nonfreeing_call_p (gimple *call)
 static bool
 check_loadstore (gimple *, tree op, tree, void *data)
 {
-  if ((TREE_CODE (op) == MEM_REF || TREE_CODE (op) == TARGET_MEM_REF)
-      && operand_equal_p (TREE_OPERAND (op, 0), (tree)data, 0))
-    return true;
+  if (TREE_CODE (op) == MEM_REF || TREE_CODE (op) == TARGET_MEM_REF)
+    {
+      /* Some address spaces may legitimately dereference zero.  */
+      addr_space_t as = TYPE_ADDR_SPACE (TREE_TYPE (op));
+      if (targetm.addr_space.zero_address_valid (as))
+	return false;
+
+      return operand_equal_p (TREE_OPERAND (op, 0), (tree)data, 0);
+    }
   return false;
 }