JDK-8251513: Code around Parse::do_lookupswitch/do_tableswitch should be cleaned up

[tobiasholenstein]

• default_cnt can be computed without using a loop:

An example of how `defaults` was computed before at parse2.cpp:521-533 with switch labels `-10`, `0`, `10`, `42` and `200`:

defaults = 0
defaults += -10 - (-2147483648)
defaults += 0 - (-10 + 1)
defaults += 10 - (0 + 1)
defaults += 42 - (10 + 1) 
defaults += 200 - (42 + 1)
defaults += 2147483647 - (200 + 1) + 1

=> `defaults`  = 
-10 - (-2147483648) + 0 - (-10 + 1) + 10 - (0 + 1) + 42 - (10 + 1) + 200 - (42 + 1) + 2147483647 - (200 + 1) + 1 = 
4294967291 = 2147483648 + 2147483648 - 5
BUT actually `defaults` was : `defaults` = 2147483648 + 2147483648

The reason has to do with using floats:
((float)match_int - (float)prev) == (-(float)prev) is True
for match_int=-10, prev=-2147483648

BUT actually `defaults` (2147483648 + 2147483648 - 5) can also be computed without using a loop with `juint defaults = max_juint - len`

• also made some casts explicit

• A lot of casts could be avoided by making _cnt in SwitchRange a uint. Unfortunately, the Range for the default values of a switch in do_lookupswitch calculates the count by scaling the average cnt/label up to cnt/range which needs a float to store an accurate result

---

Progress

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Issue

• JDK-8251513: Code around Parse::do_lookupswitch/do_tableswitch should be cleaned up

Reviewers

• Roland Westrelin (@rwestrel - Reviewer)
• Tobias Hartmann (@TobiHartmann - Reviewer)

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[tobiasholenstein]

in do_lookupswitch the ranges for the defaults values have very accurate value (by taking the average). Whereas the ranges for the defaults values in do_tableswitch are just calculated by taking profile->default_count() / 2 for the lower and upper default ranges. But this can be very imbalanced if lower and upper range for the default have very different size. Should this be changed?

[mlbridge]

Webrevs

• 00: Full (1d6f00a2)

[rwestrel]

That looks good to me.

[openjdk]

@tobiasholenstein 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:

8251513: Code around Parse::do_lookupswitch/do_tableswitch should  be cleaned up

Reviewed-by: roland, thartmann

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 145 new commits pushed to the master branch:

• 3150069: 8271949: dumppath in -XX:FlightRecorderOptions does not affect
• bfcf6a2: 8275277: assert(dest_attr.is_in_cset() == (obj->forwardee() == obj)) failed: Only evac-failed objects must be in the collection set here but is not
• 96fef40: 8189591: No way to locally suppress doclint warnings
• 7fc3a8d: 8275149: (ch) ReadableByteChannel returned by Channels.newChannel(InputStream) throws ReadOnlyBufferException
• 831802d: 8275163: Deflater::deflate methods omit javadoc for ReadOnlyBufferException
• ad9e234: 8275145: file.encoding system property has an incorrect value on Windows
• f178185: 8275249: Suppress warnings on non-serializable array component types in jdk.jlink
• ee64ce9: 8274937: Revert the timeout setting for DynamicLoaderConstraintsTest
• 8c4da9c: 8275013: Improve discussion of serialization method declarations in java.io.Object{Input, Output}Stream
• da8da3a: 8269698: Specification for methods of java.awt.im.InputContext should mention that they do nothing
• ... and 135 more: https://git.openjdk.java.net/jdk/compare/3953e0774c59c5e936e752aa08b6b6778e232994...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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[TobiHartmann]

Looks good to me too.

[tobiasholenstein]

@rwestrel and @TobiHartmann thanks for the reviews!

[tobiasholenstein]

/integrate

[openjdk]

@tobiasholenstein
Your change (at version 1d6f00a) is now ready to be sponsored by a Committer.

[TobiHartmann]

/sponsor

[openjdk]

Going to push as commit ebb1363.
Since your change was applied there have been 146 commits pushed to the master branch:

• bb7dacd: 8275334: Move class loading Events to a separate section in hs_err files
• 3150069: 8271949: dumppath in -XX:FlightRecorderOptions does not affect
• bfcf6a2: 8275277: assert(dest_attr.is_in_cset() == (obj->forwardee() == obj)) failed: Only evac-failed objects must be in the collection set here but is not
• 96fef40: 8189591: No way to locally suppress doclint warnings
• 7fc3a8d: 8275149: (ch) ReadableByteChannel returned by Channels.newChannel(InputStream) throws ReadOnlyBufferException
• 831802d: 8275163: Deflater::deflate methods omit javadoc for ReadOnlyBufferException
• ad9e234: 8275145: file.encoding system property has an incorrect value on Windows
• f178185: 8275249: Suppress warnings on non-serializable array component types in jdk.jlink
• ee64ce9: 8274937: Revert the timeout setting for DynamicLoaderConstraintsTest
• 8c4da9c: 8275013: Improve discussion of serialization method declarations in java.io.Object{Input, Output}Stream
• ... and 136 more: https://git.openjdk.java.net/jdk/compare/3953e0774c59c5e936e752aa08b6b6778e232994...master

Your commit was automatically rebased without conflicts.

[openjdk]

@TobiHartmann @tobiasholenstein Pushed as commit ebb1363.

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