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8266028: C2 computes -0.0 for Math.pow(-0.0, 0.5) #3712
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👋 Welcome back jiefu! A progress list of the required criteria for merging this PR into |
/test |
@DamonFool |
@DamonFool The |
@DamonFool This change now passes all automated pre-integration checks. ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details. After integration, the commit message for the final commit will be:
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Thanks @theRealAph for your review. |
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Looks good.
Thanks @neliasso . |
I am fine with your fix - it is rare case so we can skip 0 case. But we need to verify that Interpreter and stubs (and Java) give the same result for -0.0 in 32- and 64-bit VMs. C code uses 64-bit stub code use Integer compare which should be fine I think: Java code adds |
Hi @vnkozlov , Thanks for your review. The C code actually uses integer compare. As for the Java code, C2 will emit a Java method
Generated code by C2
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Good. Thank you for checking other places.
/integrate |
@DamonFool Since your change was applied there have been 37 commits pushed to the
Your commit was automatically rebased without conflicts. Pushed as commit 75a2354. 💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored. |
Hi all,
C2 computes -0.0 for Math.pow(-0.0, 0.5) which should be 0.0 according to the API specs.
This bug was found while I was implementing the same optimization for x86_32 (JDK-8265940).
The reason is that CmpDNode [1] doesn't distinguish -0.0 from 0.0.
Math.pow(-0.0, 0.5) was replaced with Math.sqrt(-0.0) incorrectly since CmpDNode says -0.0 < 0.0 if false.
The fix excludes C2's optimization for x=0.0/-0.0.
And the jtreg test has been improved to make sure the corner cases are covered by the compilers.
Thanks.
Best regards,
Jie
[1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/library_call.cpp#L1656
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