http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54674
--- Comment #9 from William J. Schmidt <wschmidt at gcc dot gnu.org> 2012-09-24 20:32:34 UTC --- To be clear, SLSR doesn't rely on mult costs being greater than int costs -- it simply trusts that the given costs are accurate and makes decisions based upon them. Don't worry about the power-of-two shift cases. The logic in expmed.c that SLSR, IVOPTS, and other passes rely on figures out whether a multiply-by-coefficient can be replaced by a combination of shifts/adds/subtracts based on the costs of those items versus the cost of a multiply. It's just that, as things stand, it will never believe those replacements are better since a general multiply appears to be so cheap (even a single shift/add will only be equal to a general multiply). Probably you will get some overall code gen improvement by just raising the cost of the general multiply to reflect the average cycles for a multiply of unknown values.
