[Bug tree-optimization/111445] [12/13/14 Regression] Wrong code at -Os on x86_64-linux-gnu since r12-1077-g57bf3751511

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111445

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
-Os -fallow-store-data-races -fdisable-tree-sccp -fno-tree-loop-im

makes the case simpler to look at, IVOPTs only mangles the last loop there:

Analyzing # of iterations of loop 2
  exit condition [d_26 + 1, + , 1](no_overflow) <= 1
  bounds on difference of bases: -255 ... 0
  result:
    zero if d_26 > 1
    # of iterations 1 - (unsigned int) d_26, bounded by 1
  number of iterations 1 - (unsigned int) d_26; zero if d_26 > 1
..
Selected IV set for loop 2 at t.c:22, 2 avg niters, 1 IVs:
Candidate 10:
  Var befor: ivtmp.26_28
  Var after: ivtmp.26_29
  Incr POS: at end
  IV struct:
    Type:       unsigned int
    Base:       (unsigned int) (d_26 + 1)
    Step:       1
    Biv:        N
    Overflowness wrto loop niter:       No-overflow

changing

+  _31 = d_26 + 1;
+  ivtmp.26_30 = (unsigned int) _31;
   goto <bb 6>; [100.00%]

   <bb 5> [local count: 118111600]:
   b.6_7 = b;
   _8 = (int) b.6_7;
   check (_8);
-  e_21 = e_15 + 1;
+  ivtmp.26_29 = ivtmp.26_28 + 1;

   <bb 6> [local count: 236223200]:
-  # e_15 = PHI <0(10), e_21(5)>
+  # ivtmp.26_28 = PHI <ivtmp.26_30(10), ivtmp.26_29(5)>
   _9 = (unsigned char) d_26;
   _10 = _9 + 1;
   _11 = (int) _10;
-  _12 = (int) e_15;
-  _13 = _11 + _12;
-  if (_13 <= 1)
+  _32 = (int) ivtmp.26_28;
+  if (_32 <= 1)
     goto <bb 5>; [50.00%]
   else
     goto <bb 7>; [50.00%]