[Bug tree-optimization/23902] New: update_ssa very very very slow

["dberlin at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

For 20001226-1.c at -O3, i get:

Execution times (seconds)
 tree VRP              :  11.32 (10%) usr   0.08 ( 9%) sys  11.68 (10%) wall   
3194 kB ( 8%) ggc
 tree operand scan     :  28.39 (26%) usr   0.17 (18%) sys  29.00 (25%) wall   
2722 kB ( 7%)  dominance frontiers   :  35.35 (32%) usr   0.13 (14%) sys  36.18
(31%) wall       0 kB ( 0%) ggc
 TOTAL                 : 110.77             0.92           116.23             
38719 kB

gprof shows that all but one of the calls to compute dominance frontiers come
from update_ssa (probably because people are using TODO_update_ssa instead of
TODO_update_ssa_no_phi).

The operand scan time is also mostly update_ssa, checking for modified statements

-- 
           Summary: update_ssa very very very slow
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dberlin at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23902