[Bug c++/48822] [4.5 Regression] G++ gets stucks and never finishes compilation when enabling -O2/3 optimization options.

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48822

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2011.04.29 13:58:16
      Known to work|                            |4.4.5, 4.6.0
   Target Milestone|---                         |4.5.4
            Summary|G++ gets stucks and never   |[4.5 Regression] G++ gets
                   |finishes compilation when   |stucks and never finishes
                   |enabling -O2/3 optimization |compilation when enabling
                   |options.                    |-O2/3 optimization options.
     Ever Confirmed|0                           |1
      Known to fail|                            |4.5.3

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-04-29 
13:58:16 UTC ---
Confirmed.  It's stuck in SCCVN/FRE visiting

g_37 = PHI <g_36(12), g_38(13)>
g_38 = PHI <g_35(12), g_39(13)>
g_39 = g_37 % g_38;

Value numbering g_37 stmt = g_37 = PHI <g_36(12), g_38(13)>
Setting value number of g_37 to g_37 (changed)
Value numbering g_38 stmt = g_38 = PHI <g_35(12), g_39(13)>
Setting value number of g_38 to 0 (changed)
Value numbering g_39 stmt = g_39 = g_37 % g_38;
Setting value number of g_39 to g_39 (changed)
Value numbering g_37 stmt = g_37 = PHI <g_36(12), g_38(13)>
Setting value number of g_37 to 0 (changed)
Value numbering g_38 stmt = g_38 = PHI <g_35(12), g_39(13)>
Setting value number of g_38 to g_38 (changed)
Value numbering g_39 stmt = g_39 = g_37 % g_38;
RHS g_37 % g_38 simplified to 0 has constants 1
Setting value number of g_39 to 0 (changed)

thus it oscillates.

Maybe latent everywhere else.

Workaround: -fno-tree-fre -fno-tree-pre