Ping and CC Zdenek with the right email. Thanks, bin
> -----Original Message----- > From: gcc-patches-ow...@gcc.gnu.org [mailto:gcc-patches- > ow...@gcc.gnu.org] On Behalf Of bin.cheng > Sent: Wednesday, November 06, 2013 5:51 PM > To: gcc-patches@gcc.gnu.org > Cc: Richard Biener; o...@ucw.cz > Subject: [PATCH GCC]Improve IVOPT to handle outside and inside loop iv > uses differently in GCC > > Hi, > GCC IVOPT has a problem that it doesn't differentiate between iv uses > outside of loop from inside ones. It computes cost for outside iv use just like > inside ones, which is wrong because outside iv use should be computed > along loop exit edge and the cost should be amortized against loop iteration > number. Lastly, the computation of outside iv use is inserted in loop, rather > along loop exit edge. > > This is interesting since usually outside iv use should be handled differently, > or it hurts optimization in several ways like: > 1) Wrong iv candidate is chosen because of inaccurate cost. > 2) Extra computation in loop itself is redundant. > 3) Extra code computing outside iv use in loop may increases register > pressure because both iv variables before and after stepping could be alive > at same time. > 4) IVOPT generates code that it expects to stay as is, passes like DOM tends > to break this because of the extra computation. This hurts targets with auto- > increment support more. > > This patch fixes the problem. Bootstrap and test on x86/x86_64/arm. > Richard, Zdenek, does this look reasonable? > > Thanks, > bin > > > gcc/testsuite/ChangeLog > 2013-11-06 Bin Cheng <bin.ch...@arm.com> > > * gcc.dg/tree-ssa/ivopts-outside-loop-use-1.c: New test. > > 2013-11-06 Bin Cheng <bin.ch...@arm.com> > > * tree-ssa-loop-ivopts.c (iv_use_p, iv_cand_p): Move around. > (iv_use_location): New. > (struct iv): Remove have_use_for and use_id. New fields > inside_use, outside_uses_vec and use_loc. > (struct iv_use): New fields exit_edge and outside_use_p. > (struct edge_info, edge_info_p): New. > (struct ivopts_data): New fields alloc_uses_vecs, changed_bbs, > edge_map and edge_obstack. > (init_edge_info, get_edge_info): New. > (dump_use): Dump outside/inside information for iv use. > (tree_ssa_iv_optimize_init): Init new fields. > (alloc_iv): Init new fields. Remove have_use_for and use_id. > (record_use): New parameter. Record information for outside loop > iv use. > (find_interesting_uses_op): New parameter. Handle inside and > outside loop iv uses. > (find_interesting_uses_cond, idx_record_use): Pass new argument. > (find_interesting_uses_address): Likewise. > (find_interesting_uses_stmt, create_new_iv): likewise. > (find_interesting_uses_outside): Rename exit to exit_edge. > New parameter normal_edge_p. Pass new argument. > (find_interesting_uses): Find iv uses in two passes. > (get_computation): Compute cost at right position for iv use. > (determine_use_iv_cost_generic): Ajust cost for outside loop iv use. > (rewrite_use_outside_of_loop): New. > (rewrite_use): Call rewrite_use_outside_of_loop. > (remove_unused_ivs): Keep computation only for inner iv use. > (free_loop_data): Reset outside_uses_vec in various iv structures. > Free alloc_uses_vecs and edge_map. > (tree_ssa_iv_optimize_finalize): Free and reset. > (tree_ssa_iv_optimize_loop): Create edge_map. > (tree_ssa_iv_optimize): Call rewrite_into_loop_closed_ssa if > necessary.
