RFR: 8262916: Merge LShiftCntV and RShiftCntV into a single node [v2]

[Eric Liu]

> The vector shift count was defined by two separate nodes(LShiftCntV and
> RShiftCntV), which would prevent them from being shared when the shift
> counts are the same.
> 
> 
> public static void test_shiftv(int sh) {
>     for (int i = 0; i < N; i+=1) {
>         a0[i] = a1[i] << sh;
>         b0[i] = b1[i] >> sh;
>     }
> }
> 
> 
> Given the example above, by merging the same shift counts into one
> node, they could be shared by shift nodes(RShiftV or LShiftV) like
> below:
> 
> 
> Before:
> 1184  LShiftCntV  === _  1189  [[ 1185  ... ]]
> 1190  RShiftCntV  === _  1189  [[ 1191  ... ]]
> 1185  LShiftVI  === _  1181  1184  [[ 1186 ]]
> 1191  RShiftVI  === _  1187  1190  [[ 1192 ]]
> 
> After:
> 1190  ShiftCntV  === _  1189  [[ 1191 1204  ... ]]
> 1204  LShiftVI  === _  1211  1190  [[ 1203 ]]
> 1191  RShiftVI  === _  1187  1190  [[ 1192 ]]
> 
> 
> The final code could remove one redundant “dup”(scalar->vector),
> with one register saved.
> 
> 
> Before:
>         dup     v16.16b, w12
>         dup     v17.16b, w12
>         ...
>         ldr     q18, [x13, #16]
>         sshl    v18.4s, v18.4s, v16.4s
>         add     x18, x16, x12           ; iaload
> 
>         add     x4, x15, x12
>         str     q18, [x4, #16]          ; iastore
> 
>         ldr     q18, [x18, #16]
>         add     x12, x14, x12
>         neg     v19.16b, v17.16b
>         sshl    v18.4s, v18.4s, v19.4s
>         str     q18, [x12, #16]         ; iastore
> 
> After:
>         dup	v16.16b, w11
>         ...
>         ldr	q17, [x13, #16]
>         sshl	v17.4s, v17.4s, v16.4s
>         add	x2, x22, x11            ; iaload
> 
>         add	x4, x16, x11
>         str	q17, [x4, #16]          ; iastore
> 
>         ldr	q17, [x2, #16]
>         add	x11, x21, x11
>         neg	v18.16b, v16.16b
>         sshl	v17.4s, v17.4s, v18.4s
>         str	q17, [x11, #16]         ; iastore

Eric Liu has updated the pull request incrementally with one additional commit since the last revision:

  code backup
  
  Change-Id: Ie9046b1d7e8f5e2669767756b6b074b564523039

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3371/files
  - new: https://git.openjdk.java.net/jdk/pull/3371/files/eece376d..c860c725

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3371&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3371&range=00-01

  Stats: 826 lines in 10 files changed: 324 ins; 205 del; 297 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3371.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3371/head:pull/3371

PR: https://git.openjdk.java.net/jdk/pull/3371