[Bug tree-optimization/38785] [6/7/8 Regression] huge performance regression on EEMBC bitmnp01

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38785

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|REOPENED                    |NEW
   Last reconfirmed|2010-02-19 12:17:54         |2018-2-5

--- Comment #49 from Richard Biener <rguenth at gcc dot gnu.org> ---
The testcase from comment#3 still reproduces the issue for me:

  <bb 6> [local count: 955630223]:
  # cstore_55 = PHI <2147483647(4), 0(5)>
  # prephitmp_87 = PHI <3221225470(4), 1073741823(5)>
  # prephitmp_88 = PHI <3937053352(4), 1789569705(5)>
... many more...
  # prephitmp_116 = PHI <2934894317(4), 787410670(5)>
  # prephitmp_117 = PHI <2505397588(4), 357913941(5)>
  MEM[(void *)_3] = cstore_55;
  _7 = *_4;
...

There's the old issue of PRE lacking a cost model (and undoing PRE
being impossible for these cases).