Some processor architectures do support bitwise access to memory, eg. ARM
Cortex-M and 8051 (by ARM called bit-banding).
In these architectures a single bit can somewhat be addressable, but only as an
'aliased' memory region for another memory address.
I noticed that Keil ARMCC compiler now seems to support this huge optimization
possibility.
ARMCC mark bit-bandable types as __attribute__((bitband)), then when declaring,
an reference to bit-banded memory is given.
typedef struct
{
char i : 1;
int j : 2;
int k : 3;
} BB __attribute__((bitband));
BB bb __attribute__((at(0x20000004)));
void foo(void)
{
bb.i = 1;
}
Should something similar be possible in GCC, using attributes or similar to
mark this feature possible to utilize,
then pick up this at a very late target specific optimization pass that could
use bit-banding when possible?
Like eg. a Cortex peephole2 or something similar?
Have anyone maybe already tried to look into this feature in GCC?
Is it a good idea, or even possible?
Refs:
http://www.keil.com/support/man/docs/armcc/armcc_chr1359124979689.htm
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/15921.html
https://answers.launchpad.net/gcc-arm-embedded/+question/228758
Best Regards,
Fredrik
