https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67288
--- Comment #6 from Segher Boessenkool <segher at gcc dot gnu.org> --- (In reply to Bernd Schmidt from comment #5) > (In reply to Christophe Leroy from comment #0) > > > The following section is just useless: (shift left 4 bits, remove 16, shift > > right 4 bits, add 1) > > c000d984: 55 24 20 36 rlwinm r4,r9,4,0,27 > > c000d988: 39 24 ff f0 addi r9,r4,-16 > > c000d98c: 55 29 e1 3e rlwinm r9,r9,28,4,31 > > c000d990: 39 29 00 01 addi r9,r9,1 > > Are you suggesting just removing these? That would not produce the same > value in all cases - consider zero as an input: > > ((0 << 4) - 16) >> 4 = 0xfffffff, add one and you get 0x10000000. But this cannot happen, see the two immediately preceding instructions.