A question on endGroupNode

[Doerr, Martin]

Hi Gustavo,

I can't see how endGroup nodes can get generated in the current jdk9 code.
If I remember correctly, endgroup instructions were emitted in conditional long branches when the branch destination is near. But this code is gone in the current jdk9 code.
Are you using an older version?

The purpose of endgroup instructions is to optimize for Power6. They should get inserted before control flow merge points if the instruction group is not already completed. We have a special Power6 instruction scheduler which takes care of that, but we haven't contributed it. I guess Power6 optimization is not so relevant any more.

Best regards,
Martin


-----Original Message-----
From: ppc-aix-port-dev [mailto:ppc-aix-port-dev-bounces at openjdk.java.net] On Behalf Of Gustavo Romero
Sent: Dienstag, 31. Januar 2017 12:19
To: ppc-aix-port-dev at openjdk.java.net
Subject: A question on endGroupNode
Importance: High

Hi,

Sometimes the JVM on PPC64 puts a group ending nop (ori r1,r1,0) after conditional branches, like, for instance, the following assembly sequence from
C2 generated from Hive code:

   379 6.6e-04 :    10000980436c:       lwz     r14,16(r6)
   816  0.0014 :    100009804370:       cmplw   cr6,r7,r14
               :    100009804374:       bge     cr6,100009804ee8
               :    100009804378:       ori     r1,r1,0   <=== endGroup
   167 2.9e-04 :    10000980437c:       add     r15,r7,r8
   892  0.0015 :    100009804380:       addi    r17,r15,-1
               :    100009804384:       cmplw   cr5,r17,r14
               :    100009804388:       bge     cr5,100009804ee8
   262 4.5e-04 :    10000980438c:       ori     r1,r1,0   <=== endGroup
   648  0.0011 :    100009804390:       li      r14,0
               :    100009804394:       cmpld   cr6,r5,r14
               :    100009804398:       beq     cr6,100009804ee8
   267 4.6e-04 :    10000980439c:       ori     r1,r1,0   <=== endGroup
   930  0.0016 :    1000098043a0:       addis   r20,r29,384
               :    1000098043a4:       addi    r20,r20,16384

The (ori r1, r1, 0) seems to be emitted from a endGroupNode defined in:
http://hg.openjdk.java.net/jdk9/hs/hotspot/file/6c1e79a99176/src/cpu/ppc/vm/ppc.ad#l13261

Nonetheless, I could not generated any endGroupNode using SPECjvm2008 (i.e.
looking at the log from -XX:+PrintOptoAssembly there is no "End Bundle" anywhere).

Any idea why it exists primarily and if there is any option to control its emission or even a particular way to avoid the creation of an endGroupNode?

Thank you.


Best regards,
Gustavo