[Bug tree-optimization/111003] [14 Regression] Dead Code Elimination Regression at -O3 since r14-2161-g237e83e2158

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111003

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Of course that's not really a "fix", but it's restoring of not doing the extra
hoisting.  So it does fix the regression but not maybe the underlying issue.

We're not anticipating more imprecise range-info on DEFs when hoisting here.

The "real" fix would be to improve conditional hoisting - we have

  <bb 12> [local count: 29170419070]:
  # prephitmp_61 = PHI <pretmp_60(11), prephitmp_59(10)>
  _13 = (unsigned int) _3;
  if (_3 > 6)
    goto <bb 73>; [50.00%]
  else 
    goto <bb 13>; [50.00%]

  <bb 73> [local count: 14585209535]:
  goto <bb 14>; [100.00%]

  <bb 13> [local count: 14585209535]:
  iftmp.9_18 = _13 << 6;
  _63 = _13 ^ iftmp.9_18;
  _65 = _63 != 10;

  <bb 14> [local count: 35145083376]:
  # prephitmp_66 = PHI <1(73), _65(13), 1(74)>
  # prephitmp_67 = PHI <prephitmp_61(73), prephitmp_61(13), prephitmp_59(74)>

and the diamond with if (_3 > 6) including the precceding def of _13
(which wasn't sunk) is invariant.  There's an existing bug about LIM
missing a way to hoist a sub-CFG (it can only hoist PHIs as COND_EXPRs).
It might not exactly fit "LIM" but could be integrated with this pass.

I'd say we close this bug, I'll add the testcase.