RFR(S) 8016157: During CTW: C2: assert(!def_outside->member(r)) failed: Use of external LRG overlaps the same LRG defined in this block

[Roland Westrelin]

A comment why this:

 538 
 539   if (is_ideal_negD()) {
 540     return false;
 541   }

is here would be nice.

Also why is it better to filter out NegDNodes in the adlc rather than in MachNode::rematerialize()?

Roland.