8374785: Template Library: need to tag Float16.copySign as having non-deterministic result because of multiple NaNs with different sign bits

[eme64]

This is a very similar issue as #29033 / JDK-8374489.

There are NaN encodings that have the sign bit set, and others that have it not set.
If we now copy the sign from such a NaN to a numeric value (e.g. 1), we can get 1 or -1.

jshell> var a = Float.NaN;
a ==> NaN
jshell> var b = Float.intBitsToFloat(0xFFC00000);
b ==> NaN
jshell> Math.copySign(1f, a)
==> 1.0
jshell> Math.copySign(1f, b)
==> -1.0
jshell> Float16.copySign(Float16.valueOf(1f), Float16.valueOf(a))
==> 1.0
jshell> Float16.copySign(Float16.valueOf(1f), Float16.valueOf(b))
==> -1.0

Since NaN values of different encodings are interchangable, and we cannot know what NaN we get, and hence the sign bit is arbitrary, we can also not know the sign of the result of Float16.copySign. We have to mark it as non-deterministic and hence disable result verification.

Since this is a test-bug, I have no regression test. But I verified it manually, that with the same seed (for the ExpressionFuzzer) that fails before this change, we now succeed after the change.

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Issue

• JDK-8374785: Template Library: need to tag Float16.copySign as having non-deterministic result because of multiple NaNs with different sign bits (Bug - P4)

Reviewers

• Tobias Hartmann (@TobiHartmann - Reviewer)
• Quan Anh Mai (@merykitty - Committer)

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@eme64 This change now passes all automated pre-integration checks.

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8374785: Template Library: need to tag Float16.copySign as having non-deterministic result because of multiple NaNs with different sign bits

Reviewed-by: thartmann, qamai

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At the time when this comment was updated there had been 82 new commits pushed to the master branch:

• fb13abe: 8374743: G1 starts a concurrent mark when allocating humongous objects during initialization
• 133a023: 8374471: Check bin and lib folder of JDK image for unwanted files
• 4904046: 8372302: C2: IGVN verification fails because ModXNode::Ideal creates unused intermediate nodes
• ... and 79 more: https://git.openjdk.org/jdk/compare/2cb228e142369ec73d768d8a69653a984b1c5908...master

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[TobiHartmann]

Looks good to me.

[mlbridge]

Webrevs

• 00: Full (939ab079)

[eme64]

@merykitty @TobiHartmann Thanks for the reviews!

/integrate

[openjdk]

Going to push as commit 2fbe475.
Since your change was applied there have been 83 commits pushed to the master branch:

• d0aae04: 8325108: POSIX map_memory_to_file calls release_memory unnecessarily
• fb13abe: 8374743: G1 starts a concurrent mark when allocating humongous objects during initialization
• 133a023: 8374471: Check bin and lib folder of JDK image for unwanted files
• ... and 80 more: https://git.openjdk.org/jdk/compare/2cb228e142369ec73d768d8a69653a984b1c5908...master

Your commit was automatically rebased without conflicts.

[openjdk]

@eme64 Pushed as commit 2fbe475.

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