RFR: 8234003: Improve IndexSet iteration

[Tobias Hartmann]

Hi Claes,

nice cleanup, looks good to me!

Just noticed that you've (intentionally?) changed the indentation of the comment in live.cpp:259.

Best regards,
Tobias

On 13.11.19 00:09, Claes Redestad wrote:
> Hi,
> 
> a significant portion of work done during register allocation in C2 is
> iterating over IndexSets.
> 
> A few small optimizations show a ~4% decrease in instructions retired by
> register allocation when instrumenting, and up to 3% fewer instructions
> retired in total on startup tests.
> 
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8234003
> Webrev: http://cr.openjdk.java.net/~redestad/8234003/open.00/
> 
> The biggest improvement comes from avoiding iterating over empty sets
> altogether. A smaller improvement from adding a water mark to avoid
> iterating over all the blocks in the IndexSet.
> 
> Testing: tier1-3, verified improvements on large and tiny startup tests,
> checked that any increased inlining is footprint neutral on Linux.
> 
> Thanks!
> 
> /Claes
>