8292226: Prepare make for better Link Time Optimization support

[TheShermanTanker]

The support for Link Time Optimization in the JDK's make system could do with some cleaning up, at the moment it simply assumes the compiler is gcc and sets the flags as such. Instead of introducing changes in bulk, as a first step, it would be good to simply supply the appropriate flags depending on the compiler and refine the flags for the one existing compiler with support for it. In practice the latter just means adding the proper -fuse-linker-plugin to gcc compile step when link-time-opt is specified, as without it the compiler generates both native code and information rich representation for Link Time Optimization. With this flag, native code generation is disabled and object files will contain only code required for Link Time Optimization, thus speeding up compile times as well.

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Progress

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Issue

• JDK-8292226: Prepare make for better Link Time Optimization support

Reviewers

• Magnus Ihse Bursie (@magicus - Reviewer)

Reviewing

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Update a local copy of the PR:
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$ git pull https://git.openjdk.org/jdk pull/9829/head

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[bridgekeeper]

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[openjdk]

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[mlbridge]

Webrevs

• 04: Full - Incremental (cb7ef7cc)
• 03: Full - Incremental (4921c220)
• 02: Full - Incremental (9b6195a0)
• 01: Full - Incremental (be9af820)
• 00: Full (af0bbe74)

[dholmes-ora]

I'll leave it to build folk to approve this. Making this contingent on using gcc seems reasonable. But I think we may end up just removing this anyway.

Thanks.

[TheShermanTanker]

But I think we may end up just removing this anyway.

You never know for certain if this might come in handy in the future ;)

[magicus]

Technically this change seems reasonable, but I tend to agree with David that it is more likely that a better solution would be to remove this completely. Have you tried building with LTO enabled? What kind of build times do you get -- and what kind of improvements in terms of file size and performance? My gut feeling is that there is no way that the small potential improvements can counteract the huge negative impact of build times magnitudes larger.

[magicus]

Whatever. Your patch makes the code less ugly, and possibly LTO a bit more useful. Let's save the "shall we remove this?" discussion for another day.

[openjdk]

@TheShermanTanker 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:

8292226: Prepare make for better Link Time Optimization support

Reviewed-by: ihse

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 114 new commits pushed to the master branch:

• 79597f1: 8272702: Resolving URI relative path with no / may lead to incorrect toString
• 7b5f9ed: 8288966: Better handle very spiky promotion in G1
• 07c7977: 8290249: Vectorize signum on AArch64
• a3ec0bb: 8253413: [REDO] [REDO] G1 incorrectly limiting young gen size when using the reserve can result in repeated full gcs
• 27b0f77: 8292318: Memory corruption in remove_dumptime_info
• 9a65524: 8290300: Use standard String-joining tools where applicable
• f9004fe: 8292561: Make "ReplayCompiles" a diagnostic product switch
• 2fbb936: 8292691: Move CompilerConfig::is_xxx() inline functions out of compilerDefinitions.hpp
• 3601e30: 8290909: MemoryPoolMBean/isUsageThresholdExceeded tests failed with "isUsageThresholdExceeded() returned false, and is still false, while threshold = MMMMMMM and used peak = NNNNNNN"
• 37c0a13: 8292350: Use static methods for hashCode/toString primitives
• ... and 104 more: https://git.openjdk.org/jdk/compare/4b03e135e157cb6cc9ba5eebf4a1f1b6e9143f48...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.

As you do not have Committer status in this project an existing Committer must agree to sponsor your change. Possible candidates are the reviewers of this PR (@dholmes-ora, @magicus) but any other Committer may sponsor as well.

➡️ To flag this PR as ready for integration with the above commit message, type /integrate in a new comment. (Afterwards, your sponsor types /sponsor in a new comment to perform the integration).

[TheShermanTanker]

/integrate

[openjdk]

@TheShermanTanker
Your change (at version cb7ef7c) is now ready to be sponsored by a Committer.

[magicus]

/sponsor

[openjdk]

Going to push as commit 1ed03d8.
Since your change was applied there have been 114 commits pushed to the master branch:

• 79597f1: 8272702: Resolving URI relative path with no / may lead to incorrect toString
• 7b5f9ed: 8288966: Better handle very spiky promotion in G1
• 07c7977: 8290249: Vectorize signum on AArch64
• a3ec0bb: 8253413: [REDO] [REDO] G1 incorrectly limiting young gen size when using the reserve can result in repeated full gcs
• 27b0f77: 8292318: Memory corruption in remove_dumptime_info
• 9a65524: 8290300: Use standard String-joining tools where applicable
• f9004fe: 8292561: Make "ReplayCompiles" a diagnostic product switch
• 2fbb936: 8292691: Move CompilerConfig::is_xxx() inline functions out of compilerDefinitions.hpp
• 3601e30: 8290909: MemoryPoolMBean/isUsageThresholdExceeded tests failed with "isUsageThresholdExceeded() returned false, and is still false, while threshold = MMMMMMM and used peak = NNNNNNN"
• 37c0a13: 8292350: Use static methods for hashCode/toString primitives
• ... and 104 more: https://git.openjdk.org/jdk/compare/4b03e135e157cb6cc9ba5eebf4a1f1b6e9143f48...master

Your commit was automatically rebased without conflicts.

[openjdk]

@magicus @TheShermanTanker Pushed as commit 1ed03d8.

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