[patch] Fix gnat.dg/pack19.adb on some platforms

[Eric Botcazou]

Hi,

the new test gnat.dg/pack19.adb doesn't pass on some platforms because of the 
target-dependent result of loads from bit-fields with size 0.

Unlike the stores to these bit-fields which are handled in an uniform way in 
store_field:

  /* If we have nothing to store, do nothing unless the expression has
     side-effects.  */
  if (bitsize == 0)
    return expand_expr (exp, const0_rtx, VOIDmode, EXPAND_NORMAL);

the result of the loads depends on SHIFT_COUNT_TRUNCATED: the result is 0 if 
the macro is 0, otherwise it's garbage.  The attached patch makes it so that 
the result is always 0 independently of the target.

Tested on x86/Linux and PowerPC/Linux, OK for the mainline?


2013-12-09  Eric Botcazou  <ebotca...@adacore.com>

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


-- 
Eric Botcazou
Index: expr.c
===================================================================
--- expr.c	(revision 205774)
+++ expr.c	(working copy)
@@ -10177,6 +10177,12 @@ expand_expr_real_1 (tree exp, rtx target
 		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.  */
+	    if (bitsize == 0)
+	      return const0_rtx;
+
 	    op0 = validize_mem (op0);
 
 	    if (MEM_P (op0) && REG_P (XEXP (op0, 0)))