RFR: 8240220: IdealLoopTree::dump_head predicate printing is broken

[Stefan Karlsson]

Hi all,

Please review this patch to fix the loop predicate printing in 
IdealLoopTree::dump_head.

https://cr.openjdk.java.net/~stefank/8240220/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8240220

In GraphKit::add_predicate you can see the order in which the 
predicates are added:

     add_predicate_impl(Deoptimization::Reason_predicate, nargs);
     add_predicate_impl(Deoptimization::Reason_profile_predicate, nargs);
     add_predicate_impl(Deoptimization::Reason_loop_limit_check, nargs);

When IdealLoopTree::dump_head looks for these predicates, the code has 
incorrectly swapped the 'predicate' and 'profile_predicate':

2541   Node* predicate = 
PhaseIdealLoop::find_predicate_insertion_point(entry, 
Deoptimization::Reason_loop_limit_check);
2547     entry = PhaseIdealLoop::find_predicate_insertion_point(entry, 
Deoptimization::Reason_predicate);
2554     entry = PhaseIdealLoop::find_predicate_insertion_point(entry, 
Deoptimization::Reason_profile_predicate);

(Note that the predicates are added top-down, while dump_head walks them 
bottom-up)

The code also uses wrong node when calling skip_loop_predicates. Compare 
the skipping of 'limit_check':

2541   Node* predicate = 
PhaseIdealLoop::find_predicate_insertion_point(entry, 
Deoptimization::Reason_loop_limit_check);
2542   if (predicate != NULL ) {
2543     tty->print(" limit_check");
2544     entry = PhaseIdealLoop::skip_loop_predicates(entry);

and see how the skipping of 'predicate' sets entry on line 2547;
2547     entry = PhaseIdealLoop::find_predicate_insertion_point(entry, 
Deoptimization::Reason_predicate);
2548     if (entry != NULL) {
2549       tty->print(" predicated");
2550       entry = PhaseIdealLoop::skip_loop_predicates(entry);
2551     }

Before the patch, the 'profile_predicated' and 'predicated' items were 
missing:
   Loop: N344/N304  limit_check counted [0,int),+1 (-1 iters)  has_sfpt

After the patch, the lines look like this:
   Loop: N344/N304  limit_check profile_predicated predicated counted 
[0,int),+1 (-1 iters)  has_sfpt

I've only tested this by visually inspecting the output. I don't know if 
there are any existing tests for this kind of code in the Compiler.

Thanks,
StefanK