[Bug rtl-optimization/84003] FAIL: g++.dg/torture/pr77745.C with noinline foo

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84003

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |alias, wrong-code
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2018-01-24
                 CC|                            |rguenth at gcc dot gnu.org
          Component|target                      |rtl-optimization
            Summary|FAIL:                       |FAIL:
                   |g++.dg/torture/pr77745.C    |g++.dg/torture/pr77745.C
                   |with -fpic                  |with noinline foo
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Goes wrong during sched2 which re-orders the read and writes in
foo:

foo (char * c1, char * c2)
{
  long int _7;

  <bb 2> [local count: 1073741825]:
  MEM[(long int *)c1_1(D)] = 100;
  MEM[(long long int *)c2_4(D)] = 200;
  MEM[(long int *)c2_4(D)] = 200;
  _7 = MEM[(long int *)c1_1(D)];
  return _7;

compiles to

_Z3fooPcS_:
.LFB1:
        .cfi_startproc
        movl    4(%esp), %eax
        movl    8(%esp), %edx
        movl    $100, (%eax)
        movl    (%eax), %eax
        movl    $200, (%edx)
        movl    $0, 4(%edx)
        ret

note c1_1 == c2_4.  This must be a latent bug in scheduling somehow not
triggered without -fpic (inlining probably).  Indeed, marking foo as
noinline makes it trigger without -fpic.