[Bug middle-end/57790] New: Waste work in can_move_insns_across()

[pchang9 at cs dot wisc.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57790

            Bug ID: 57790
           Summary: Waste work in can_move_insns_across()
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pchang9 at cs dot wisc.edu
                CC: nistor1 at illinois dot edu

Created attachment 30429
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30429&action=edit
Suggested patch

The problem appears in revision 200588 in version 4.9. I have attached a
one-line patch that fixes it.

In method "can_move_insns_across()" in df-problems.c, the loop on line 4038
should break immediately after "fail" is set to 1. All the iterations after
"fail" set to 1 do not perform any useful work, at best they just set "fail"
again to 1.