ObjectiveC. Computation of offsets when doing @encode type encoding
is only used in an assert. Do not do it if assert is not on.
80 col. comment.
indvars: sink truncates outside the loop.

This is a follow up of the r198338 commit that added truncates for
lcssa phi nodes. Sinking the truncates below the phis cleans up the
loop and simplifies subsequent analysis within the indvars pass.