re PR middle-end/50266 (ICE in decode_addr_const)

	PR middle-end/50266
	* c-common.c (c_fully_fold_internal) <ADDR_EXPR>: Fold offsetof-like
	computations.

From-SVN: r178611

gcc/c-family/ChangeLog

+2011-09-06  Eric Botcazou  <ebotcazou@adacore.com>
+
+	PR middle-end/50266
+	* c-common.c (c_fully_fold_internal) <ADDR_EXPR>: Fold offsetof-like
+	computations.
+
 2011-09-05  Richard Guenther  <rguenther@suse.de>
 
 	* c-common.c (complete_array_type): Use ssize_int (-1) instead

gcc/c-family/c-common.c

@@ -1264,7 +1264,20 @@ c_fully_fold_internal (tree expr, bool in_init, bool *maybe_const_operands,
       STRIP_TYPE_NOPS (op0);
       if (code != ADDR_EXPR && code != REALPART_EXPR && code != IMAGPART_EXPR)
 	op0 = decl_constant_value_for_optimization (op0);
-      if (op0 != orig_op0 || in_init)
+      /* ??? Cope with user tricks that amount to offsetof.  The middle-end is
+	 not prepared to deal with them if they occur in initializers.  */
+      if (op0 != orig_op0
+	  && code == ADDR_EXPR
+	  && (op1 = get_base_address (op0)) != NULL_TREE
+	  && TREE_CODE (op1) == INDIRECT_REF
+	  && TREE_CONSTANT (TREE_OPERAND (op1, 0)))
+	{
+	  tree offset = fold_offsetof (op0, op1);
+	  op1
+	    = fold_convert_loc (loc, TREE_TYPE (expr), TREE_OPERAND (op1, 0));
+	  ret = fold_build_pointer_plus_loc (loc, op1, offset);
+	}
+      else if (op0 != orig_op0 || in_init)
 	ret = in_init
 	  ? fold_build1_initializer_loc (loc, code, TREE_TYPE (expr), op0)
 	  : fold_build1_loc (loc, code, TREE_TYPE (expr), op0);

gcc/testsuite/ChangeLog

+2011-09-06  Eric Botcazou  <ebotcazou@adacore.com>
+
+        * gcc.c-torture/compile/20110906-1.c: New test.
+
 2011-09-06  Uros Bizjak  <ubizjak@gmail.com>
 
 	* gcc.target/i386/builtin-apply-mmx.c: Require ia32 effective target.

gcc/testsuite/gcc.c-torture/compile/20110906-1.c

+/* PR middle-end/50266 */
+/* Testcase by <bero@arklinux.org> */
+
+struct a {
+ unsigned int a;
+ unsigned int b;
+};
+
+struct a *const p = (struct a *)0x4A004100;
+
+void foo(void)
+{
+ unsigned int i = 0;
+ unsigned int *const x[] = {
+  &p->a,
+  &p->b,
+  0
+ };
+
+ (*(volatile unsigned int *)((x[i]))
+   = (unsigned int)((unsigned int)((*(volatile unsigned int *)(x[i])))));
+}