[aarch64-port-dev ] RFR: 8224828: aarch64: save and restore the rflags register in push_CPU_state and pop_CPU_state

[Yangfei (Felix)]

Hi,

    Please review: 
        JBS: https://bugs.openjdk.java.net/browse/JDK-8224828
        Webrev: http://cr.openjdk.java.net/~fyang/8224828/webrev.00/

    Currently, the rflags register is not handled in push_CPU_state and pop_CPU_state for the aarch64 port (including aarch64-8u, jdk11 and jdk13).  
    This is causing random Hadoop Terasort failure using an aarch64-8u jvm.  
    After some further investigation, we located the problematic C2 JIT code snippet:  

1190   0x0000ffff785f8a1c: lsr       x14, x15, x11
1191   0x0000ffff785f8a20: lsr       x11, x6, x11
1192   0x0000ffff785f8a24: and       x11, x11, #0xff
1193   0x0000ffff785f8a28: and       x14, x14, #0xff
1194   0x0000ffff785f8a2c: sub       x11, x14, x11
1195   0x0000ffff785f8a30: mov       w14, w11
1196   0x0000ffff785f8a34: cmp       w14, #0x0
1197   0x0000ffff785f8a38: cset      w15, lt             ;*invokeinterface compare
1198                                                 ; - org.apache.hadoop.mapred.Merger$MergeQueue::lessThan at 70 (line 658)
1199                                                 ; - org.apache.hadoop.util.PriorityQueue::downHeap at 41 (line 141)
1200                                                 ; - org.apache.hadoop.util.PriorityQueue::adjustTop at 1 (line 108)
1201                                                 ; - org.apache.hadoop.mapred.Merger$MergeQueue::adjustPriorityQueue at 59 (line 595)
1202                                                 ; - org.apache.hadoop.mapred.Merger$MergeQueue::next at 25 (line 618)
1203
1204   0x0000ffff785f8a3c: cmp       w14, #0x0                                   <====================
1205   0x0000ffff785f8a40: adrp      x11, 0x0000ffff88830000
1206                                                 ;   {poll}
1207   0x0000ffff785f8a44: mov       w17, w20         ; OopMap{r17=NarrowOop [32]=Oop [40]=Oop [56]=Oop [64]=Oop [80]=NarrowOop off=1224}
1208                                                 ;*ifeq
1209                                                 ; - org.apache.hadoop.util.PriorityQueue::downHeap at 121 (line 149)
1210                                                 ; - org.apache.hadoop.util.PriorityQueue::adjustTop at 1 (line 108)
1211                                                 ; - org.apache.hadoop.mapred.Merger$MergeQueue::adjustPriorityQueue at 59 (line 595)
1212                                                 ; - org.apache.hadoop.mapred.Merger$MergeQueue::next at 25 (line 618)
1213

1214   0x0000ffff785f8a48: ldr       wzr, [x11]          ;   {poll}                   <====================

1215   0x0000ffff785f8a4c: csel      w24, w12, w10, lt    ;*invokevirtual compareTo    <====================
1216                                                 ; - org.apache.hadoop.io.FastByteComparisons$LexicographicalComparerHolder$UnsafeComparer::compareTo at 16 (     line 132)
1217                                                 ; - org.apache.hadoop.io.FastByteComparisons::compareTo at 11 (line 46)
1218                                                 ; - org.apache.hadoop.io.WritableComparator::compareBytes at 8 (line 188)
1219                                                 ; - org.apache.hadoop.io.Text$Comparator::compare at 39 (line 368)
1220                                                 ; - org.apache.hadoop.mapred.Merger$MergeQueue::lessThan at 70 (line 658)
1221                                                 ; - org.apache.hadoop.util.PriorityQueue::downHeap at 41 (line 141)
1222                                                 ; - org.apache.hadoop.util.PriorityQueue::adjustTop at 1 (line 108)
1223                                                 ; - org.apache.hadoop.mapred.Merger$MergeQueue::adjustPriorityQueue at 59 (line 595)
1224                                                 ; - org.apache.hadoop.mapred.Merger$MergeQueue::next at 25 (line 618)

    At line 1204, the rflags register is defined and it will be used at line 1215.  There is a safepoint poll in between at line 1214. 
    Safepoint is requested at line 1214 and control flow continues in the code generated by SafepointBlob* SharedRuntime::generate_handler_blob. 
    This blob calls save_live_register and restore_live_registers which will finally calls push_CPU_state and pop_CPU_state. 
    As the rflags register is not saved and restored by push_CPU_state and pop_CPU_state, we got an invalid rflags at line 1215. 
    Patch fixes the issue for jdk13 by saving and restoring the rflags register in push_CPU_state and pop_CPU_state respectively. 

Thanks,
Felix