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

[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

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Commit messages:
 - 8265940: Enable C2's optimization for Math.pow(x, 0.5) on all platforms

Changes: https://git.openjdk.java.net/jdk/pull/3755/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3755&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265940
  Stats: 21 lines in 3 files changed: 14 ins; 4 del; 3 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