Backport two upstream patches for bitfield volatile bug.

r171347 and r181549
http://gcc.gnu.org/viewcvs?view=revision&revision=181549
http://gcc.gnu.org/ml/gcc-patches/2011-03/msg01477.html

Change-Id: I3f0a433e32eb26015be6173a3b52aac0f6fecf7d

4 files changed, 51 insertions, 2 deletions

diff --git a/gcc-4.6/gcc/ChangeLog.google-4_6 b/gcc-4.6/gcc/ChangeLog.google-4_6
index 732ae610f..309acfb48 100644
--- a/gcc-4.6/gcc/ChangeLog.google-4_6
+++ b/gcc-4.6/gcc/ChangeLog.google-4_6
@@ -1,3 +1,16 @@
+2011-12-05  Jing Yu  <jingyu@google.com>
+
+	Backport r171347 and r181549 from trunk.
+	2011-03-23  Julian Brown  <julian@codesourcery.com>
+
+		* expr.c (expand_expr_real_1): Only use BLKmode for volatile
+		accesses which are not naturally aligned.
+
+	2011-11-20  Joey Ye  <joey.ye@arm.com>
+	
+		* expr.c (expand_expr_real_1): Correctly handle strict volatile
+		bitfield loads smaller than mode size.
+
 2011-08-16  Guozhi Wei  <carrot@google.com>
 
 	Backport r174965 from trunk.
diff --git a/gcc-4.6/gcc/expr.c b/gcc-4.6/gcc/expr.c
index 31f04e301..5cb5df7a2 100644
--- a/gcc-4.6/gcc/expr.c
+++ b/gcc-4.6/gcc/expr.c
@@ -9192,8 +9192,16 @@ expand_expr_real_1 (tree exp, rtx target, enum machine_mode tmode,
 		&& modifier != EXPAND_CONST_ADDRESS
 		&& modifier != EXPAND_INITIALIZER)
 	    /* If the field is volatile, we always want an aligned
-               access. */
-	    || (volatilep && flag_strict_volatile_bitfields > 0)
+	       access.  Do this in following two situations:
+	       1. the access is not already naturally
+	       aligned, otherwise "normal" (non-bitfield) volatile fields
+	       become non-addressable.
+	       2. the bitsize is narrower than the access size. Need
+	       to extract bitfields from the access.  */
+	    || (volatilep && flag_strict_volatile_bitfields > 0
+		&& (bitpos % GET_MODE_ALIGNMENT (mode) != 0 
+		    || (mode1 != BLKmode
+		        && bitsize < GET_MODE_SIZE (mode1) * BITS_PER_UNIT)))
 	    /* If the field isn't aligned enough to fetch as a memref,
 	       fetch it as a bit field.  */
 	    || (mode1 != BLKmode
diff --git a/gcc-4.6/gcc/testsuite/ChangeLog.google-4_6 b/gcc-4.6/gcc/testsuite/ChangeLog.google-4_6
index d0899f72f..15808132a 100644
--- a/gcc-4.6/gcc/testsuite/ChangeLog.google-4_6
+++ b/gcc-4.6/gcc/testsuite/ChangeLog.google-4_6
@@ -1,3 +1,8 @@
+2011-12-05  Jing Yu  <jingyu@google.com>
+
+	Backport r171347 and r181549 from trunk.
+	2011-11-20  Joey Ye  <joey.ye@arm.com>
+
 2011-08-17  Guozhi Wei  <carrot@google.com>
 
 	Backport r177357 from trunk.
diff --git a/gcc-4.6/gcc/testsuite/gcc.dg/volatile-bitfields-1.c b/gcc-4.6/gcc/testsuite/gcc.dg/volatile-bitfields-1.c
new file mode 100644
index 000000000..6adda27fe
--- /dev/null
+++ b/gcc-4.6/gcc/testsuite/gcc.dg/volatile-bitfields-1.c
@@ -0,0 +1,23 @@
+/* { dg-options "-fstrict-volatile-bitfields" } */
+/* { dg-do run } */
+
+extern int puts(const char *);
+extern void abort(void) __attribute__((noreturn));
+
+typedef struct {
+  volatile unsigned short a:8, b:8;
+} BitStruct;
+
+BitStruct bits = {1, 2};
+
+void check(int i, int j)
+{
+  if (i != 1 || j != 2) puts("FAIL"), abort();
+}
+
+int main ()
+{
+  check(bits.a, bits.b);
+
+  return 0;
+}