RFR: 8266267: Remove unnecessary jumps in Intel Math Library StubRoutines

[Jie Fu]

Hi all,

May I get reviews for this small change?

If I look at the StubRoutines::libmPow carefully, an unnecessary jump instruction can be found, which is generated here [1].

- - - [BEGIN] - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
StubRoutines::libmPow [0x00007f0f8455ddd1, 0x00007f0f8455ef05] (4404 bytes)
--------------------------------------------------------------------------------
  0x00007f0f8455ddd1:   push   %rbp
  0x00007f0f8455ddd2:   mov    %rsp,%rbp
  0x00007f0f8455ddd5:   jmpq   0x00007f0f8455ddda          <--- unnecessary jump
  0x00007f0f8455ddda:   sub    $0x28,%rsp
  0x00007f0f8455ddde:   vmovsd %xmm0,0x8(%rsp)
  0x00007f0f8455dde4:   vmovsd %xmm1,0x10(%rsp)
  ...


And similar issues can be found for StubRoutines::libmLog and StubRoutines::libmExp.

- - - [BEGIN] - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
StubRoutines::libmLog [0x00007f3fb94d48a6, 0x00007f3fb94d4b22] (636 bytes)
--------------------------------------------------------------------------------
  0x00007f3fb94d48a6:   push   %rbp
  0x00007f3fb94d48a7:   mov    %rsp,%rbp
  0x00007f3fb94d48aa:   jmpq   0x00007f3fb94d48af          <--- unnecessary jump
  0x00007f3fb94d48af:   sub    $0x18,%rsp
  0x00007f3fb94d48b3:   vmovsd %xmm0,(%rsp)
  0x00007f3fb94d48b8:   movabs $0x3ff0000000000000,%rax
  ...



- - - [BEGIN] - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
StubRoutines::libmExp [0x00007f3fb94d4579, 0x00007f3fb94d48a6] (813 bytes)
--------------------------------------------------------------------------------
  0x00007f3fb94d4579:   push   %rbp
  0x00007f3fb94d457a:   mov    %rsp,%rbp
  0x00007f3fb94d457d:   jmpq   0x00007f3fb94d4582          <--- unnecessary jump
  0x00007f3fb94d4582:   sub    $0x18,%rsp
  0x00007f3fb94d4586:   vmovsd %xmm0,0x8(%rsp)
  0x00007f3fb94d458c:   vunpcklpd %xmm0,%xmm0,%xmm0


I can't find a reason why we need an extra jump there.
So I suggest removing them.

Testing:
  - tier1 ~ tier3 on Linux/x64, no regression

Am I missing something?

Thanks.
Best regards,
Jie

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

Commit messages:
 - 8266267: Remove unnecessary jumps in Intel Math Library StubRoutines

Changes: https://git.openjdk.java.net/jdk/pull/3784/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3784&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266267
  Stats: 7 lines in 3 files changed: 2 ins; 5 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3784.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3784/head:pull/3784

PR: https://git.openjdk.java.net/jdk/pull/3784