RFR: 8303278: Imprecise bottom type of ExtractB/UB

[Eric Liu]

This is a trivial patch, which fixes the bottom type of ExtractB/UB nodes.

ExtractNode can be generated by Vector API Vector.lane(int), which gets the lane element at the given index. A more precise type of range can help to optimize out unnecessary type conversion in some cases.

Below shows a typical case used ExtractBNode


  public static byte byteLt16() {
   ByteVector vecb = ByteVector.broadcast(ByteVector.SPECIES_128, 1);
   return vecb.lane(1);
  }


In this case, c2 constructs IR graph like:

    ExtractB  ConI(24)
       |     __|
       |    /  |
    LShiftI  __|
       |    /
    RShiftI

which generates AArch64 code:

  movi    v16.16b, #0x1
  smov    x11, v16.b[1]
  sxtb    w0, w11

with this patch, this shift pair can be optimized out by RShiftI's identity [1]. The code is optimized to:

  movi    v16.16b, #0x1
  smov    x0, v16.b[1]

[TEST]

Full jtreg passed except 4 files on x86:

jdk/incubator/vector/Byte128VectorTests.java
jdk/incubator/vector/Byte256VectorTests.java
jdk/incubator/vector/Byte512VectorTests.java
jdk/incubator/vector/Byte64VectorTests.java

They are caused by a known issue on x86 [2].

[1] https://github.com/openjdk/jdk/blob/742bc041eaba1ff9beb7f5b6d896e4f382b030ea/src/hotspot/share/opto/mulnode.cpp#L1052
[2] https://bugs.openjdk.org/browse/JDK-8303508

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

Commit messages:
 - 8303278: Imprecise bottom type of ExtractB/UB

Changes: https://git.openjdk.org/jdk/pull/13070/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13070&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303278
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13070.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13070/head:pull/13070

PR: https://git.openjdk.org/jdk/pull/13070