After MachineSink, there will be peephole opportunity for:
%0:g8rc_and_g8rc_nox0 = ADDI8 %5:g8rc_and_g8rc_nox0, 144 STD killed %7:g8rc, 16, %0:g8rc_and_g8rc_nox0 :: (store 8 into %ir.8)
STD killed %7:g8rc, 160, %5:g8rc_and_g8rc_nox0 :: (store 8 into %ir.8)
This folding opportunity may become unfoldable after RA because we may redefine addi's register operand in RA. So we add this peephole before RA in convertToImmediateForm.
This patch tries to do this.