Hi Diego,
This is a backport for two upstream patches into our 4.6 branch.
I submitted the first patch by Julian a while ago for backport but
Richard Earnshaw pointed out a problem with the first patch. The second
patch from Joey fixes that problem. This was tested on x86 and ARM.
-Doug
2011-11-22 Doug Kwan <dougk...@google.com>
Backport r171347 and r181549 from trunk.
gcc/
2011-03-23 Julian Brown <jul...@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...@arm.com>
* expr.c (expand_expr_real_1): Correctly handle strict volatile
bitfield loads smaller than mode size.
gcc/testsuite/
2011-11-20 Joey Ye <joey...@arm.com>
* gcc.dg/volatile-bitfields-1.c: New.
Index: gcc/testsuite/gcc.dg/volatile-bitfields-1.c
===================================================================
--- gcc/testsuite/gcc.dg/volatile-bitfields-1.c (revision 0)
+++ gcc/testsuite/gcc.dg/volatile-bitfields-1.c (revision 0)
@@ -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;
+}
Index: gcc/expr.c
===================================================================
--- gcc/expr.c (revision 181550)
+++ gcc/expr.c (working copy)
@@ -9200,8 +9200,16 @@
&& 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
--
This patch is available for review at http://codereview.appspot.com/5434084
