RFR: 8265940: Enable C2's optimization for Math.pow(x, 0.5) on all platforms [v2]

[Jie Fu]

> Hi all,
> 
> I'd like to enable C2's optimization for Math.pow(x, 0.5) on all platforms.
> 
> This is fine because:
>  1) For x86, it will call the assembly stubs.
>     This opt has already been implemented for x86_64 [1]. 
>     And the x86_32 version is added in this patch.
>  2) For non-x86, it will call the shared runtime c code [2], which does the same opt too.
> 
> Testing:
>   - tier1~3 on Linux/{x86_32, x86_64}, no regression
> 
> Thanks,
> Best regards,
> Jie
> 
> 
> [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/x86/macroAssembler_x86_pow.cpp#L838
> [2] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/runtime/sharedRuntimeTrans.cpp#L497

Jie Fu has updated the pull request incrementally with one additional commit since the last revision:

  Add comments for why -0.0/0.0 are excluded

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3755/files
  - new: https://git.openjdk.java.net/jdk/pull/3755/files/bb88f24f..0b3203ac

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3755&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3755&range=00-01

  Stats: 6 lines in 2 files changed: 6 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3755.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3755/head:pull/3755

PR: https://git.openjdk.java.net/jdk/pull/3755