https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92822
--- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Richard Sandiford <rsand...@gcc.gnu.org>: https://gcc.gnu.org/g:1ee3b380dfb479b335f3b50039ce26abcbffe59a commit r10-6280-g1ee3b380dfb479b335f3b50039ce26abcbffe59a Author: Richard Sandiford <richard.sandif...@arm.com> Date: Sat Jan 25 17:18:51 2020 +0000 forwprop: Tweak choice of VEC_PERM_EXPR filler [PR92822] For the 2s failures in the PR, we have a V4SF VEC_PERM_EXPR in which the first two elements are duplicates of one element and the other two are don't-care: v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, ?, ? }>; The heuristic was to extend this with a blend: v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, 2, 3 }>; but it seems better to extend a partial duplicate to a full duplicate: v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, 1, 1 }>; Obviously this is still just a heuristic though. I wondered whether to restrict this to two elements or more but couldn't find any examples in which it made a difference. Either way should be fine for the purposes of fixing this PR. 2020-01-28 Richard Sandiford <richard.sandif...@arm.com> gcc/ PR tree-optimization/92822 * tree-ssa-forwprop.c (simplify_vector_constructor): When filling out the don't-care elements of a vector whose significant elements are duplicates, make the don't-care elements duplicates too.
