RFR: 8344607: Link Time Optimization - basic support for clang

[Lutz Schmidt]

On Wed, 27 Nov 2024 15:14:10 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> Support the clang toolchain when link time optimization is configured.
> Please note that this is NOT intended to enable lto by default and NOT to fix all possible clang-supporting builds or test issues .
> 
> It works on my Linux x86_64 SUSE 15 test machine with  clang15.0.7, also on macOS with Xcode 13.1 devkit  and Xcode 15.4 .
> 
> To be able to build on macOS with Xcode, I had to deal with one issue.  The lto-link process runs into this error 
> 
> 
> ld: <inline asm>:11:1: symbol 'SpinPause_return' is already defined
> SpinPause_return:        
> ^
> for architecture arm64
> clang: error: linker command failed with exit code 1 (use -v to see invocation)
> 
> 
> Seems that when building with LTO,  the  inline assembler code in SpinPause() is not handled well. In the lto inlining the label  SpinPause_return is generated multiple times and causes an 'already defined' error. This goes away when adding NOINLINE to this function.
> Linux/clang did not show this issue, probably the toolchain there does not have the error.

LGTM.

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Marked as reviewed by lucy (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22412#pullrequestreview-2465384466