On Mon, Jul 02, 2007 at 10:17:13AM -0700, Ian Lance Taylor wrote: > volatile uint32_t* ptr = .....; > uint32_t v = *ptr; > v = (v & 0xffffff00) | 123; > *ptr = v; > > Note that if you don't use the volatile qualifier, gcc is wholly > capable of optimizing that into an 8-bit memory write. Or more precisely, it used to, and we intend it to regain that capability in the future. See bug 15184. When it comes to a back end solution, one existing target (MT) has an option to not generate byte loads and stores, and there was a long thread about modifying the ARM back end to generate byte writes such that, at the hardware level, they would become a cache line wide read-modify-write access. Search the GCC mailing list for this: Modifying ARM code generator for elimination of 8bit writes - need help The ARM solution relies on assistance form the hardware, so I suggest you look at the MT back end first to see if it does something clever. -- Rask Ingemann Lambertsen
