re PR tree-optimization/22278 (gcc -O2 discards cast to volatile)

        PR tree-opt/22278
        * gimplify.c (gimplify_expr): Use main variant type for the temp
        destination for a discarded volatile read.
        * tree-ssa.c (tree_ssa_useless_type_conversion_1): Don't elide
        casts between non-void types that change volatility.

From-SVN: r102169

gcc/ChangeLog

+2005-07-19  Richard Henderson  <rth@redhat.com>
+
+	PR tree-opt/22278
+	* gimplify.c (gimplify_expr): Use main variant type for the temp
+	destination for a discarded volatile read.
+	* tree-ssa.c (tree_ssa_useless_type_conversion_1): Don't elide
+	casts between non-void types that change volatility.
+
 2005-07-15  DJ Delorie  <dj@redhat.com>
 
 	* toplev.h: Add comment about the first parameter for warning().

gcc/gimplify.c

@@ -4411,8 +4411,9 @@ gimplify_expr (tree *expr_p, tree *pre_p, tree *post_p,
 	{
 	  /* Historically, the compiler has treated a bare
 	     reference to a volatile lvalue as forcing a load.  */
-	  tree tmp = create_tmp_var (TREE_TYPE (*expr_p), "vol");
-	  *expr_p = build (MODIFY_EXPR, TREE_TYPE (tmp), tmp, *expr_p);
+	  tree type = TYPE_MAIN_VARIANT (TREE_TYPE (*expr_p));
+	  tree tmp = create_tmp_var (type, "vol");
+	  *expr_p = build (MODIFY_EXPR, type, tmp, *expr_p);
 	}
       else
 	/* We can't do anything useful with a volatile reference to

gcc/tree-ssa.c

@@ -903,6 +903,15 @@ tree_ssa_useless_type_conversion_1 (tree outer_type, tree inner_type)
 	   && TREE_CODE (TREE_TYPE (outer_type)) == VOID_TYPE)
     return true;
 
+  /* Don't lose casts between pointers to volatile and non-volatile
+     qualified types.  Doing so would result in changing the semantics
+     of later accesses.  */
+  else if (POINTER_TYPE_P (inner_type)
+           && POINTER_TYPE_P (outer_type)
+	   && TYPE_VOLATILE (TREE_TYPE (outer_type))
+	      != TYPE_VOLATILE (TREE_TYPE (inner_type)))
+    return false;
+
   /* Pointers/references are equivalent if their pointed to types
      are effectively the same.  This allows to strip conversions between
      pointer types with different type qualifiers.  */