https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54236
--- Comment #16 from Oleg Endo <olegendo at gcc dot gnu.org> --- Created attachment 36012 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36012&action=edit addsicc pattern (In reply to Oleg Endo from comment #9) > The following function compiled with -O2 > > unsigned int check (unsigned int x) > { > return x == 0 ? 1 : x; > } > > results in: > tst r4,r4 > bt/s .L7 > mov #1,r0 > mov r4,r0 > .L7: > rts > nop > > > Writing it as: > unsigned int check (unsigned int x) > { > return x + (x == 0); > } > > results in: > tst r4,r4 > mov #0,r0 > rts > addc r4,r0 > > It seems that ifcvt is trying to utilize the 'add<mode>cc' standard name > pattern. If the 2nd operand of the conditional addition is a constant 1 or > -1 the addcc insn can be implemented via addc or subc without a branch. The attached patch adds support for the addsicc pattern and a few other improvements. However, the first case above doesn't see any improvement. It seems that it's a missed ifcvt optimization.
