On Mon, Nov 14, 2011 at 4:58 AM, Yuehai Du <duyue...@gmail.com> wrote: > Hi > > i found IVOPTS didn't work well on some case if the loop contain > some unaligned access. it didn't take this kind of memory access into > account because this check in function:find_interesting_uses_address > > /* Moreover, on strict alignment platforms, check that it is > sufficiently aligned. */ > if (STRICT_ALIGNMENT && may_be_unaligned_p (base, step)) > goto fail; > > and this is used to fix http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17949 > because it converting byte loads into a unaligned word load on strict > alignment platform. > > but there are some platform which is strict alignment and it also > support unaligned access for special mode. for example, ARM NEON support > vector mode unaligned access via VLD1/VST1, and they both support write back > address mode. > > Moreover, lately ARM add unaligned access support for all ARMv6 , ARMv7-A, > ARMv7-R, and ARMv7-M architecture-based processors which controlled by the > option: munaligned-access. > see http://gcc.gnu.org/ml/gcc-patches/2011-05/msg00513.html. > > so what should we do now? should we use target hook to check this or > something else?
Huh, IVOPTs should never cause a different size memory read. I wonder if the original issue would still reproduce with the fix reverted. Can you ponder in this direction (thus, remove the may_be_unaligned_p check completely)? Richard. > -- > Yuehai Du >
