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This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes
process, proposals are publicly announced in order to receive
community feedback. This proposal will only be implemented if approved
by the Fedora Engineering Steering Committee.

== Summary ==
Update all llvm sub-projects in Fedora Linux to version 19.

== Owner ==
* Name: [[User:tstellar| Tom Stellard]]
* Email: <>

== Detailed Description ==

All llvm sub-projects in Fedora will be updated to version 19, and
there will be a soname version change for the llvm libraries.
Compatibility packages clang18, llvm18, lld18, compiler-rt18, and
libomp18 will be added to ensure that packages that currently depend
on clang and llvm version 18 libraries will continue to work. We may
add other compatibility packages too if they're determined to be
necessary to maintain functionality in other RPMS that use llvm/clang.
Any compatibility packages we add for Fedora 41 will be retired or
orphaned before the Fedora 42 branch date.  As stated in the
[[Changes/LLVM-18 | LLVM-18 change proposal]], we plan to retire or
orphan these older compatibility packages prior to the Fedora 41
branch date:

* llvm17
* clang17
* lld17
* compiler-rt17
* libomp17

Other notable changes:

* '''Build compat packages (e.g. llvm18) as early as possible.'''
When we package a new major release of llvm, we create a compat
package so that packages that aren't compatible with the new version
can still use the old version.  In the past, we've waited to introduce
the compat packages until the new version of LLVM was ready (typically
during the Beta Freeze).  However, this proved to be an issue this
release for packages the were ready to switch to the compat packages
early in the release cycle, but then had to wait for Beta freeze.

* '''Spec file merge.'''  We plan to retire the clang, compiler-rt,
lld and libomp packages and merge them in with llvm and have them be
sub-packages of the llvm package.  All these packages have their
sources in the same upstream git repository and use the same
versioning.  This change will allow us to use the build configuration
recommended by upstream and also make it possible to optimize the
packages using Profile-Guided Optimizations (PGO).  It's possible that
in future releases (f42+), we may decided to merge more packages in
with llvm too.

* '''Fat LTO'''. All RPMS built with clang will default to using the
-ffat-lto option.  Fat LTO is a feature that allows the compiler to
produce libraries that contain LTO bitcode along side the traditional
ELF binary code so that the libraries can be linked in both LTO mode
and non-LTO mode. gcc also supports this feature and has it enabled in
Fedora. In Fedora 40 and older, with LTO enabled, clang produces
binaries with only LTO bitcode, so we need to run a post-processing
script (brp-llvm-compile-to-elf) on the libraries to convert them to
ELF code so they can be used by other packages. Enabling Fat LTO will
allow us to remove this script and simplify the build process.  We
originally proposed this feature for Fedora 40, but it was not ready
in time.

===Planned Schedule===

Our plan is to push 19.1.0-rc3 into Fedora 41 as a Beta Freeze
exception.  Updates after 19.1.0-rc3 will generally be very small and
can be done after the Beta Freeze is over.  If we are late packaging
releases after 19.1.0-rc3, we will not ask for a Final Freeze
exception, unless they contain a fix for a critical release blocking

We are not planning to push 19.1.0-rc1 into rawhide because the
library ABI is not stabilized at that point. Typically, the ABI
stabilizes after -rc3, but there are no guarantees from upstream about
this.  Given the history of minimal ABI changes after -rc3, we feel
like it's safe to push -rc3 into rawhide and Fedora 41.  The worst
case scenario would be an ABI change in -rc4 or the final release that
would force us to patch LLVM to maintain compatibility with the -rc3
ABI.  This scenario would not require rebuilding LLVM library users in
Fedora, so it would merely be a self-contained change to LLVM.

====Important Dates====

Dates may change depending on circumstances.

* Jun   4: Build llvm18, clang18, lld18, compiler-rt18, and lld18
compat packages in rawhide.
* July 26: Begin building LLVM 19.1.0-rc1 in COPR.
* Aug   6: Begin building LLVM 19.1.0-rc2 in COPR.
* '''''Aug   6: Fedora f41 branches created.'''''
* Aug  20: Begin building LLVM 19.1.0-rc3 in Rawhide and f41 side-tags.
* '''''Aug  20: Fedora f41 Beta Freeze'''''
* Aug  20-> Sep 10: Request Beta Freeze Exception and push 19.1.0-rc3
into f41 stable.
* Sep   3: Begin building LLVM 19.1.0-rc4 in Rawhide side-tag.
* Sep  17: Begin building LLVM 19.1.0 in Rawhide and f41 side-tags.
* Sep  17 -> Oct 1: Push 19.1.0 into f41 stable.
* '''''Oct   1: Fedora f41 Final Freeze.'''''

== Feedback ==

== Benefit to Fedora ==

New features and bug fixes provided by the latest version of LLVM.

== Scope ==
* Proposal owners:
** Review existing llvm and clang compatibility packages and orphan
any packages that are no longer used.
** Build and test early release candidates of LLVM 19 in COPR.

* Other developers:
** Fix build issues found with LLVM-19 or switch their package to use
the llvm18 compat libs.  The LLVM team will not block Bodhi updates on
dependent packages that fail to build or run with LLVM-19.  There
should be around 6-8 weeks between when -rc1 lands in the koji
side-tag and the Final Freeze for package maintainers to fix issues
uncovered with the LLVM-19 update.

* Release engineering: []

* Policies and guidelines: N/A (not needed for this Change)

* Trademark approval: N/A (not needed for this Change)

* Alignment with the Fedora Strategy:

== Upgrade/compatibility impact ==

This change should not impact upgrades.

== Early Testing (Optional) ==

Do you require 'QA Blueprint' support? N

== How To Test ==

The CI tests for the llvm sub-packages in Fedora will be used to catch
regressions that might be potentially introduced by the update to LLVM

== User Experience ==

== Dependencies ==

Packages that depend on one of the llvm packages will need to be
updated to work with LLVM19 or will need to switch to using one of the
llvm18 compat packages.

== Contingency Plan ==

If there are major problems with LLVM 19, the compatibility package
provide a way for other packages to continue using LLVM 18.

* Contingency deadline:Final Freeze

* Blocks release? No (not a System Wide Change)

== Documentation ==

LLVM sub-projects in Fedora have been updated to version 19:

* llvm (now includes clang, lld, compiler-rt, libomp)
* lldb
* llvm-test-suite
* libcxx
* python-lit
* flang
* mlir
* polly
* libclc
* llvm-bolt

== Release Notes ==

Aoife Moloney

Fedora Operations Architect

Fedora Project


IRC: amoloney
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