https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/178924
Backport 88478ab495f27f2cb798d4bf6912fe7cf4872997 Requested by: @bd1976bris >From f9ea9c9d79dc3aee710f2c8f6c3d2e39b23810fe Mon Sep 17 00:00:00 2001 From: Ben Dunbobbin <[email protected]> Date: Fri, 30 Jan 2026 16:17:20 +0000 Subject: [PATCH] [DOC][DTLTO] Update DTLTO documentation for the LLVM 22 release (#177368) This change updates the documentation to reflect work completed during the LLVM 22 timeframe, including support for the ThinLTO cache and static libraries/archives. It also clarifies that the goal of DTLTO is to support distribution of ThinLTO backend compilations for any in-process ThinLTO invocation. SIE Internal Tracker: TOOLCHAIN-21016 (cherry picked from commit 88478ab495f27f2cb798d4bf6912fe7cf4872997) --- llvm/docs/DTLTO.rst | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-) diff --git a/llvm/docs/DTLTO.rst b/llvm/docs/DTLTO.rst index 70e26efed897e..c4df0e15977ef 100644 --- a/llvm/docs/DTLTO.rst +++ b/llvm/docs/DTLTO.rst @@ -24,7 +24,11 @@ here: Using the *separate thin-link* approach requires a build system capable of handling the dynamic dependencies specified in the individual summary index files, such as Bazel. DTLTO removes this requirement, allowing it to be used -with any build process that supports in-process ThinLTO. +with any build process that supports in-process ThinLTO. To facilitate this, +DTLTO supports common in-process ThinLTO features, such as caching. Bitcode +objects in static libraries/archives (e.g. libc.a) are also handled +transparently by temporarily extracting referenced objects for distribution; +when thin archives are used, no extraction is required. The following commands show the steps used for the *separate thin-link* approach for a basic example: @@ -66,7 +70,7 @@ such as the following can be used: .. code-block:: console - clang -flto=thin -fuse-ld=lld -O2 t1.o t2.o -fthinlto-distributor=$(which python3) \ + clang -flto=thin -fuse-ld=lld -O2 t1.o t2.o libt3.a -fthinlto-distributor=$(which python3) \ -Xthinlto-distributor=$LLVMSRC/llvm/utils/dtlto/local.py Distributors @@ -165,17 +169,18 @@ following backend compilation commands with maximum parallelism: /usr/bin/clang -O2 -c -fprofile-sample-use=my.prof t2.o -fthinlto-index=t2.o.thinlto.bc -o t2.native.o \ -fproc-stat-report=t2.stats.txt -TODOs ------ +Limitations +----------- -The following features are planned for DTLTO but not yet implemented: +The following features are not implemented at this time: -- Support for the ThinLTO in-process cache. - Support for platforms other than ELF and COFF. -- Support for archives with bitcode members. -- Support for more LTO configurations; only a very limited set of LTO - configurations is supported currently, e.g., support for basic block sections - is not currently available. +- Support for more CodeGen configurations in the LTO backend; only a very + limited set is supported currently, e.g. support for basic block sections is + not currently available. +- Support for sharing ThinLTO cache entries with in-process ThinLTO entries. + This is not currently supported because identical code generation is not yet + guaranteed. Constraints ----------- @@ -183,4 +188,3 @@ Constraints - Matching versions of Clang and LLD should be used. - The distributor used must support the JSON schema generated by the version of LLD in use. - _______________________________________________ llvm-branch-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
