[Bug tree-optimization/100063] New: VN predication is weak

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100063

            Bug ID: 100063
           Summary: VN predication is weak
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

We are currently handling the following in FRE1, if you drop the *other = 1
store we run into the limitation that we record predicated values
"on BBs" (the single_pred_p condition in vn_nary_op_insert_pieces_predicated)
which results in this artificial limitation when considering optimistic
VN and not executable edges.  Predicates should be recorded on edges instead.

void bar ();
void foo (int pred, int *other)
{
  *other = 0;
  if (*other)
    goto cnt;
  if (pred)
    { 
      *other = 1; // necessary
cnt:  
      if (!pred)
        bar ();
    }
}