On Mon, Jun 11, 2012 at 3:16 PM, Richard Earnshaw <rearn...@arm.com> wrote: > The ARM ABI states that vectors larger than 64 bits in size still have > 64-bit alignment; never-the-less, the HW supports alignment hints of up > to 128-bits in some cases and will trap in a vector has an alignment > that less than the hint. GCC currently hard-codes larger vectors to be > aligned by the size of the vector, which means that 128-bit vectors are > marked as being 128-bit aligned. > > The ARM ABI unfortunately does not support generating such alignment for > parameters passed by value and this can lead to traps at run time. It > seems that the best way to solve this problem is to allow the back-end > to set an upper limit on the alignment permitted for a vector. > > I've implemented this as a separate hook, rather than using the existing > hooks because there's a strong likelihood of breaking some existing ABIs > if I did it another way. > > There are a couple of tests that will need some re-working before this > can be committed to deal with the fall-out of making this change; I'll > prepare those changes if this patch is deemed generally acceptable.
Hm. Where would you use that target hook? Richard. > R. > > * target.def (TARGET_VECTOR_ALIGNMENT): New hook. > * doc/tm.texi.in (TARGET_VECTOR_ALIGNMENT): Likewise. > * doc/tm.texi: Regenerate. > * targhooks.c (default_vector_alignment): New function. > * arm.c (arm_vector_alignment): New function. > (TARGET_VECTOR_ALIGNMENT): Define.
