[backport from ARM/embedded-4_6-branch, fix PR51200 yet another strict volatile bitfields bug for ARM <mikpe@it.uu.se>]

From: "Joey Ye" <joey dot ye at arm dot com>
To: <gcc-patches at gcc dot gnu dot org>
Subject: [arm-embedded] Fix restrict volatile bitfield
List-Archive: <http://gcc.gnu.org/ml/gcc-patches/>

Committed to ARM/embedded-4_6-branch

	Partly apply restrict volatile bitfield fix from bernd.
	2010-12-02  Bernd Schmidt  <bernds_cb1@t-online.de>

	* expr.c (store_field): Avoid a direct store if the mode is larger
	than the size of the bit field.
	* stor-layout.c (layout_decl): If flag_strict_volatile_bitfields,
	treat non-volatile bit fields like volatile ones.

testsuite:

	2011-11-23  Joey Ye  <joey.ye@arm.com>
	* g++.dg/abi/bitfield12.C: Add option
	-fno-strict-volatile-bitfields.

--- gcc-4.6.2/gcc/expr.c.~1~	2011-08-10 11:17:32.000000000 +0200
+++ gcc-4.6.2/gcc/expr.c	2011-12-10 16:08:44.000000000 +0100
@@ -5861,6 +5861,8 @@ store_field (rtx target, HOST_WIDE_INT b
 		|| bitpos % GET_MODE_ALIGNMENT (mode))
 	       && SLOW_UNALIGNED_ACCESS (mode, MEM_ALIGN (target)))
 	      || (bitpos % BITS_PER_UNIT != 0)))
+	      || (bitsize >= 0 && mode != BLKmode
+		  && GET_MODE_BITSIZE (mode) > bitsize)
       /* If the RHS and field are a constant size and the size of the
 	 RHS isn't the same size as the bitfield, we must use bitfield
 	 operations.  */
--- gcc-4.6.2/gcc/stor-layout.c.~1~	2011-04-05 16:34:51.000000000 +0200
+++ gcc-4.6.2/gcc/stor-layout.c	2011-12-10 16:08:44.000000000 +0100
@@ -660,12 +660,13 @@ layout_decl (tree decl, unsigned int kno
 	  /* See if we can use an ordinary integer mode for a bit-field.
 	     Conditions are: a fixed size that is correct for another mode,
 	     occupying a complete byte or bytes on proper boundary,
-	     and not volatile or not -fstrict-volatile-bitfields.  */
+	     and not -fstrict-volatile-bitfields.  If the latter is set,
+	     we unfortunately can't check TREE_THIS_VOLATILE, as a cast
+	     may make a volatile object later.  */
 	  if (TYPE_SIZE (type) != 0
 	      && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST
 	      && GET_MODE_CLASS (TYPE_MODE (type)) == MODE_INT
-	      && !(TREE_THIS_VOLATILE (decl)
-		   && flag_strict_volatile_bitfields > 0))
+	      && flag_strict_volatile_bitfields <= 0)
 	    {
 	      enum machine_mode xmode
 		= mode_for_size_tree (DECL_SIZE (decl), MODE_INT, 1);
--- gcc-4.6.2/gcc/testsuite/g++.dg/abi/bitfield12.C.~1~	2003-09-15 02:27:16.000000000 +0200
+++ gcc-4.6.2/gcc/testsuite/g++.dg/abi/bitfield12.C	2011-12-10 16:08:44.000000000 +0100
@@ -1,4 +1,4 @@
-// { dg-options "-Wabi -fabi-version=1" }
+// { dg-options "-Wabi -fabi-version=1 -fno-strict-volatile-bitfields" }
 
 struct S { // { dg-warning "ABI" }
   char c : 1024; // { dg-warning "width" }