On 25 September 2014 21:11, Joerg Wunsch <j...@uriah.heep.sax.de> wrote: > As Christian Schmidt wrote: > >> Is it fair to conclude that the ~ >> operator, applied to an unsigned char, does produce an int as output >> instead of the input type? > > Yes, this is exactly what the C standard promotion rules require. > > Well, to be exact, they *require* it behaves "as if" it were promoted > to "int", so if the sign extension has no net effect to the result, it > might be left out as well. So in that sense, it might be considered a > "missed optimization" bug in GCC here, but it's probably always hard > to catch all those situations well were the integer promotion could be > bypassed.
The first principle is to split all the multi-word operations into single operations to expose them to the late rtl optimizers, but the branches need some more specific peepholes.
avr-opt-promotion
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