[Bug tree-optimization/66131] New: [6 Regression] Wrong code w/ -O2 -ftree-loop-linear

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66131

            Bug ID: 66131
           Summary: [6 Regression] Wrong code w/ -O2 -ftree-loop-linear
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

gcc produces wrong code w/ -ftree-loop-linear -O2 (and above) for the following
reduced case:

int fk = 0;
int vm, ft;

static int
qr(void)
{
  int *op[33] = { &fk };
  int **ts[1] = { &op[0] };
  for (fk = 0; fk < 2; ++fk)
    for (ft = 0; ft < 1; ++ft)
      vm = fk;
  return 0;
}

static int
ay(void)
{
  int yc;
  for (ft = 0; ft < 1; ++ft)
    for (vm = 0; vm < 1; ++vm) {
      fk |= 1;
      return qr();
    }
  for (fk = 0; fk < 1; ++fk)
    for (yc = 0; yc < 2; ++yc)
      for (vm = 0; vm < 1; ++vm)
        for (ft = 0; ft < 1; ++ft) {
        }
  return 0;
}

int
main(void)
{
  ay();
  return vm != 1;
}

Expected results:
% gcc-6.0.0-alpha20150503 -ftree-loop-linear -O2 -Wall -Wextra -Wpedantic
dfc7c304.c
% ./a.out
% echo $?
0

Actual results:
% gcc-6.0.0-alpha20150503 -ftree-loop-linear -O2 -Wall -Wextra -Wpedantic
dfc7c304.c
% ./a.out
% echo $?
1

This issue may be somewhat similar to PR63602.