[aarch64-port-dev ] RFR: 8191954: AArch64: disable UseCISCSpill in C2

Andrew Dinn adinn at redhat.com
Tue Nov 28 09:35:09 UTC 2017

On 28/11/17 08:49, Andrew Haley wrote:
> On 28/11/17 05:54, Ningsheng Jian wrote:
>> JBS:
>> https://bugs.openjdk.java.net/browse/JDK-8191954
>> Webrev:
>> http://cr.openjdk.java.net/~njian/8191954/webrev.00/
>> This sets UseCISCSpill to false on AArch64, as we actually don't use
>> that. jtreg tests passed with fastdebug build.
> That's too risky right now.  We'll look at it in the next cycle.
I don't think it is actually /risky/ because UseCISCSpill would only
take effect if aarch64.ad declared a cisc_spilling_operand_name in the
frame section (it doesn't).

That declaration drives adlc to generate an overriding version of a
virtual method of class Node which is used by the chaitin allocator to
determine how to spill a value. Without any override the method always
returns -1, meaning that operands are never considered for CISC spilling.

So, leaving UseCISCSpill set to true causes a small amount of extra
checking to be done but no action is ever taken. Of course that also
means the change is not going to be /critical/ to performance i.e.
rushing to squeeze it into jdk10 is not justified.


Andrew Dinn
Senior Principal Software Engineer
Red Hat UK Ltd
Registered in England and Wales under Company Registration No. 03798903
Directors: Michael Cunningham, Michael ("Mike") O'Neill, Eric Shander

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