On Thu, 2014-09-18 at 09:12 -0400, David Edelsohn wrote: > On Thu, Sep 18, 2014 at 8:42 AM, Alan Lawrence <alan.lawre...@arm.com> wrote: > > The direction of VEC_RSHIFT_EXPR has been endian-dependent, contrary to the > > general principles of tree. This patch updates fold-const and the vectorizer > > (the only place where such expressions are created), such that > > VEC_RSHIFT_EXPR always shifts towards element 0. > > > > The tree code still maps directly onto the vec_shr_optab, and so this patch > > *will break any bigendian platform defining the vec_shr optab*. > > --> For AArch64_be, patch follows next in series; > > --> For PowerPC, I think patch/rfc 15 should fix, please inspect; > > --> For MIPS, I think patch/rfc 16 should fix, please inspect. > > > > gcc/ChangeLog: > > > > * fold-const.c (const_binop): VEC_RSHIFT_EXPR always shifts towards > > element 0. > > > > * tree-vect-loop.c (vect_create_epilog_for_reduction): always > > extract > > the result of a reduction with vector shifts from element 0. > > > > * tree.def (VEC_RSHIFT_EXPR, VEC_LSHIFT_EXPR): Comment shift > > direction. > > > > * doc/md.texi (vec_shr_m, vec_shl_m): Document shift direction. > > > > Testing Done: > > > > Bootstrap and check-gcc on x86_64-none-linux-gnu; check-gcc on > > aarch64-none-elf. > > Why wasn't this tested on the PowerLinux system in the GCC Compile Farm? > > Also, Bill Schmidt can help check the PPC parts fo the patches.
Sorry for the late response; I just returned from vacation. I think that patch 15 looks reasonable on the surface, but would be more comfortable if it had been tested. I would echo David's suggestion that you please test this on gcc110 in the compile farm to avoid surprises. Given the similarity between vec_shl_<mode> and vec_shr_<mode> I am ok with removing the former; it won't be difficult to re-create it later if needed. Please add some of the language you used above about VEC_RSHIFT_EXPR as commentary for vec_shr_<mode> in vector.md, as right-shifting towards element zero is not an obvious concept on a BE machine. Thanks, Bill > > Thanks, David >
