Request for reviews (XS): 6823453: DeoptimizeALot causes fastdebug server jvm to fail with assert(false,"unscheduable graph")

[John Rose]

On Mar 31, 2009, at 10:24 PM, Vladimir Kozlov wrote:

> The code in GraphKit::new_array replaces a negative constant with
> TOP (CastII(-1)#0) for all uses if it is used as new array length.
> Incorrect ideal graph is generated as result.

I think there the bug may still be present if length is not constant  
but in a negative range.

Change new byte[(byte)1.0E10] to new byte[(byte)var_1 - 128] and see  
what happens.

In that case, the type of length is int:[-256..-1], and your change  
will not have an effect.

I think this might be a more robust version of your change:

    if (map()->find_edge(length) >= 0) {
      Node* ccast = alloc->make_ideal_length(ary_type, &_gvn);
      if (ccast != length) {
        _gvn.set_type_bottom(ccast);
  +     if (!_gvn.type(ccast)->empty()) {
	 record_for_igvn(ccast);
	 replace_in_map(length, ccast);
  +     }
      }

(BTW, the logic of narrow_size_type is a little funky, since it  
returns 0 for top.  That was fixing some other, similar bug, I think.   
But maybe it should have returned a sentinel value of -1 instead of  
0.  That would not be a point-fix.)

-- John