Richard Earnshaw <rearn...@arm.com> writes: > On Fri, 2009-03-06 at 16:09 +0100, Paolo Bonzini wrote: >> If this does not work, on ARM you can also hope for something like this: >> >> ADD R0, R1, R2 >> XORS R0, R2, R3 >> XORSMI R1, R2, R3 >> SWIMI #trap > > On ARM you can just check for overflow directly... > > ADDS R0, R1, R2 > SWIVS #trap
This point should not be missed. Some processors (MIPS) have trapping arithmetic instructions, but many processors have an overflow flag which can be tested. Any useful design for -ftrapv needs to make it possible to use that overflow flag in the generated code. It will always be more efficient than using arithmetic to check for overflow. Ian
