http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49807
--- Comment #3 from Georg-Johann Lay <gjl at gcc dot gnu.org> 2011-07-21 20:34:14 UTC --- > (In reply to comment #2) > That's not quite correct. In avr-libc the header file sfr_defs.h will define a > register as this: > > #define SPDR (*((volatile char *) 0x2c)) (volatile char *) is the same as (char volatile *). Don't confuse it with (char * volatile) etc. > Is your intent to change the address AND remove the volatile keyword? I changed to different addresses in the non-volatile example because otherwise just the last store will survive. > Overall, though, I think you're on the right track. Most users would like to > be > able to do the shift-and-assign pattern in C and have it compile to storing > the > individual byte without a shift in the assembly. Right now, the only way to do > a workaround to achieve that result is through the use of a union with a > struct > and an integer type (like a long). If this issue can be fixed then I think > that > this has a chance to reduce a lot of code size problems. I don't know the exact rationale why volatile_ok is false in combine. It' obviously about volatile correctnet, but I don't see what would break here.
