Do not swing down volatile nodes

[a7ehuo]

Volatile nodes should always be anchored under a treetop to avoid any interference with other optimization passes (e.g. PRE).

Fixes eclipse-openj9/openj9#18777

[a7ehuo]

An example of with this change

Without this change (baseline), a load of volatile symbol n94n is eventually buried down under a store node n98n

n95n      treetop                                                                             [0x7fa5dd46fd70] bci=[-1,42,12] rc=0 vc=270 vn=- li=-1 udi=- nc=1
n92n        iloadi  Test.b I[#425  Shadow +8] [flags 0x603 0x0 ] (cannotOverflow )            [0x7fa5dd46fc80] bci=[-1,38,12] rc=2 vc=270 vn=- li=- udi=- nc=1 flg=0x1000
n91n          aload  <'this' parm LTest;>[#422  Parm] [flags 0x40000107 0x0 ] (X!=0 X>=0 )    [0x7fa5dd46fc30] bci=[-1,36,12] rc=2 vc=270 vn=- li=- udi=- nc=0 flg=0x104
n98n      istorei  Test.b I[#425  Shadow +8] [flags 0x603 0x0 ]                               [0x7fa5dd46fe60] bci=[-1,46,12] rc=0 vc=270 vn=- li=-1 udi=- nc=2
n91n        ==>aload
n97n        ishr                                                                              [0x7fa5dd46fe10] bci=[-1,45,12] rc=1 vc=270 vn=- li=- udi=- nc=2
n92n          ==>iloadi
n94n          iloadi  Test.c B[#446  volatile Shadow +12] [flags 0x2601 0x0 ] (cannotOverflow )  [0x7fa5dd46fd20] bci=[-1,42,12] rc=1 vc=270 vn=- li=- udi=- nc=1 flg=0x1000
n93n            aload  <'this' parm LTest;>[#422  Parm] [flags 0x40000107 0x0 ] (X!=0 X>=0 )  [0x7fa5dd46fcd0] bci=[-1,41,12] rc=1 vc=270 vn=- li=- udi=- nc=0 flg=0x104
n101n    

With this change, a load of volatile symbol n94n remains under the treetop node.

n95n      treetop                                                                             [0x7f26a0985d70] bci=[-1,42,12] rc=0 vc=270 vn=- li=-1 udi=- nc=1
n92n        iloadi  Test.b I[#425  Shadow +8] [flags 0x603 0x0 ] (cannotOverflow )            [0x7f26a0985c80] bci=[-1,38,12] rc=2 vc=270 vn=- li=- udi=- nc=1 flg=0x1000
n91n          aload  <'this' parm LTest;>[#422  Parm] [flags 0x40000107 0x0 ] (X!=0 X>=0 )    [0x7f26a0985c30] bci=[-1,36,12] rc=2 vc=270 vn=- li=- udi=- nc=0 flg=0x104
n96n      treetop                                                                             [0x7f26a0985dc0] bci=[-1,42,12] rc=0 vc=270 vn=- li=-1 udi=- nc=1
n94n        iloadi  Test.c B[#446  volatile Shadow +12] [flags 0x2601 0x0 ] (cannotOverflow )  [0x7f26a0985d20] bci=[-1,42,12] rc=2 vc=270 vn=- li=- udi=- nc=1 flg=0x1000
n93n          aload  <'this' parm LTest;>[#422  Parm] [flags 0x40000107 0x0 ] (X!=0 X>=0 )    [0x7f26a0985cd0] bci=[-1,41,12] rc=1 vc=270 vn=- li=- udi=- nc=0 flg=0x104
n98n      istorei  Test.b I[#425  Shadow +8] [flags 0x603 0x0 ]                               [0x7f26a0985e60] bci=[-1,46,12] rc=0 vc=270 vn=- li=-1 udi=- nc=2
n91n        ==>aload
n97n        ishr                                                                              [0x7f26a0985e10] bci=[-1,45,12] rc=1 vc=270 vn=- li=- udi=- nc=2
n92n          ==>iloadi
n94n          ==>iloadi

[a7ehuo]

@vijaysun-omr May I ask you to review this change? Thank you!

@hzongaro fyi

[vijaysun-omr]

jenkins build all

[vijaysun-omr]

jenkins build win

[vijaysun-omr]

Test have passed apart from known issues. The change is a conservative one that is cross platform. Merging.