RFR: 8322694: C1: Handle Constant and IfOp in NullCheckEliminator [v2]

[Denghui Dong]

On Tue, 6 Feb 2024 23:01:41 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Denghui Dong has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   update
>
> src/hotspot/share/c1/c1_Optimizer.cpp line 1218:
> 
>> 1216: 
>> 1217: void NullCheckEliminator::handle_IfOp(IfOp *x) {
>> 1218:   if (x->type()->is_object() && set_contains(x->tval()) && set_contains(x->fval())) {
> 
> What if x->tval() or x->fval() are also IfOp's?  Does NullCheckEliminator visit those depth-first?

Good catch.
I updated the patch to visit `IfOp` directly, and now it can cover the case where `IfOp`'s `tval` or `fval` are also `IfOp`.


  // Iterate through block, updating state.
  for (Instruction* instr = block; instr != nullptr; instr = instr->next()) {
    // Mark instructions in this block as visitable as they are seen
    // in the instruction list.  This keeps the iteration from
    // visiting instructions which are references in other blocks or
    // visiting instructions more than once.
    mark_visitable(instr);
    if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != nullptr)
        || (instr->as_Constant() != nullptr && instr->as_Constant()->type()->is_object())
        || (instr->as_IfOp() != nullptr)) {
      mark_visited(instr);
      instr->input_values_do(this);
      instr->visit(&_visitor);
    }
  }

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PR Review Comment: https://git.openjdk.org/jdk/pull/17191#discussion_r1480745026