Request for reviews (L): 6894779: Loop Predication for Loop Optimizer in C2

Changpeng Fang Changpeng.Fang at Sun.COM
Fri Jan 8 11:06:50 PST 2010

6894779: Loop Predication for Loop Optimizer in C2

Loop Predication Description:
The idea is to insert a predicate on the entry path to a loop, and raise 
a uncommon trap
if the check of the condition(s) fails. The condition checks are 
promoted from inside the
loop body, and thus the checks inside the loop could be eliminated.
Currently implementation works for array range checks and (loop) 
invariant checks (null
checks, array checks, etc.)

Loop Predication Advantages:
(1) No pre- and post-loops required. As a result, the optimization 
applies to the whole loop
     body. In addition, the code size increase due to the optimization 
is very limited (we don't
     need three copies of the loop)
(2) In this implementation, we apply loop predication to each level of 
the loop, so that additional
     optimization opportunities have been explored.
(3) Because it doesn't create pre- and post-loops, loop predication can 
be applied to loops with calls.

Reviewed by:
This work was initiated by Ross Knippel and has been directed and 
pre-reviewed by
Thomas Rodriguez and Vladimir Kozlov (many thanks)

JPRT, refworkload, CTW, specjvm2008



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