re PR tree-optimization/83326 (SPEC CPU2017 648.exchange2_s ~6% performance regression with r255267 (reproducer attached))
2017-12-14 Richard Biener <rguenther@suse.de>
PR tree-optimization/83326
* tree-ssa-loop-ivcanon.c (try_unroll_loop_completely): Add
may_be_zero parameter and handle it by not marking the first
peeled copy as not exiting the loop.
(try_peel_loop): Likewise.
(canonicalize_loop_induction_variables): Use number_of_iterations_exit
to handle the case of constant or zero iterations and perform
loop header copying on-the-fly.
* gcc.dg/tree-ssa/pr81388-2.c: Adjust.
From-SVN: r255635
