Georg-Johann Lay schreef op 2012-07-27 16:06:
Wouter van Gulik schrieb:Hi list, This code: char* f(char* p) { p++; return p; } Results in:mov r18,r24 mov r19,r25 subi r18,lo8(-(1)) sbci r19,hi8(-(1)) mov r24,r18 mov r25,r19 ret When compiling with avr-gcc -O[23s] -mmcu=avr5 -S main.c
Oops, copy paste error; for avr5 movw is used to move the pointer registers. Still it does a useless move.
Looks very much like PR52278, which is still open.
I think this is the same, for sanity I also checked with int and long (against my Ubuntu gcc-avr 4.5.3) and it yields the same result; first move the register then the add, then move it back.
What I wonder: why is r18 picked? Clearly r26, or r30 are way better choices. Maybe this is fixed in 4.7.1 already, don't have a 4.7+ at the moment.
According to Vladimir, the register allocator (RA) should work smooth with SUBREGs, but obviously, it does not.
Clearly.
You can try -fno-split-wide-types, but that might have other disadvantages.
That gives the expected result. HTH, Wouter _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org https://lists.nongnu.org/mailman/listinfo/avr-gcc-list
