expr.c (expand_expr_real_1): Always return 0 for the extraction of a bit-field of null size.

	* expr.c (expand_expr_real_1) <normal_inner_ref>: Always return 0 for
	the extraction of a bit-field of null size.

From-SVN: r205855

gcc/ChangeLog

+2013-12-10  Eric Botcazou  <ebotcazou@adacore.com>
+
+	* expr.c (expand_expr_real_1) <normal_inner_ref>: Always return 0 for
+	the extraction of a bit-field of null size.
+
 2013-12-10  Marek Polacek  <polacek@redhat.com>
 
 	PR sanitizer/59437

gcc/expr.c

@@ -10157,6 +10157,8 @@ expand_expr_real_1 (tree exp, rtx target, enum machine_mode tmode,
 		if (target == 0)
 		  target = assign_temp (type, 1, 1);
 
+		/* ??? Unlike the similar test a few lines below, this one is
+		   very likely obsolete.  */
 		if (bitsize == 0)
 		  return target;
 
@@ -10177,6 +10179,13 @@ expand_expr_real_1 (tree exp, rtx target, enum machine_mode tmode,
 		return target;
 	      }
 
+	    /* If we have nothing to extract, the result will be 0 for targets
+	       with SHIFT_COUNT_TRUNCATED == 0 and garbage otherwise.  Always
+	       return 0 for the sake of consistency, as reading a zero-sized
+	       bitfield is valid in Ada and the value is fully specified.  */
+	    if (bitsize == 0)
+	      return const0_rtx;
+
 	    op0 = validize_mem (op0);
 
 	    if (MEM_P (op0) && REG_P (XEXP (op0, 0)))