-- a later optimisation step on Cmm).
--
cmmOffset :: CmmExpr -> Int -> CmmExpr
+cmmOffset e 0 = e
cmmOffset (CmmReg reg) byte_off = cmmRegOff reg byte_off
cmmOffset (CmmRegOff reg m) byte_off = cmmRegOff reg (m+byte_off)
cmmOffset (CmmLit lit) byte_off = CmmLit (cmmOffsetLit lit byte_off)