[Bug gcov-profile/108658] [GCOV] Function entry is not recorded in a function containing an infinite loop from another thread depending on the optimization level

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108658

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
The relevant optimization happens in invariant motion which applies
store-motion to

void * idle (void * ignored)
{
  long int PROF_edge_counter_1;
  long int PROF_edge_counter_2;

  <bb 2> [local count: 10631108]:

  <bb 3> [local count: 1073741824]:
  PROF_edge_counter_1 = __gcov0.idle[0];
  PROF_edge_counter_2 = PROF_edge_counter_1 + 1;
  __gcov0.idle[0] = PROF_edge_counter_2;
  goto <bb 3>; [100.00%]

producing

void * idle (void * ignored)
{
  long int __gcov0.idle_I_lsm.4;
  long int PROF_edge_counter_1;
  long int PROF_edge_counter_2;

  <bb 2> [local count: 10631108]:
  __gcov0.idle_I_lsm.4_7 = __gcov0.idle[0];

  <bb 3> [local count: 1073741824]:
  # __gcov0.idle_I_lsm.4_6 = PHI <__gcov0.idle_I_lsm.4_7(2),
__gcov0.idle_I_lsm.4_8(4)>
  PROF_edge_counter_1 = __gcov0.idle_I_lsm.4_6;
  PROF_edge_counter_2 = PROF_edge_counter_1 + 1;
  __gcov0.idle_I_lsm.4_8 = PROF_edge_counter_2;

  <bb 4> [local count: 1073741824]:
  goto <bb 3>; [100.00%]

that's not wrong I think.  With -fprofile-update=atomic that doesn't
happen but the atomic update call never gets a location assigned, instead
we rely on the stmt-begin/end notes here?

void * idle (void * ignored)
{
  <bb 2> [local count: 10631108]:

  <bb 3> [local count: 1073741824]:
  __atomic_fetch_add_8 (&__gcov0.idle[0], 1, 0);
  goto <bb 3>; [100.00%]