AcoSail/llvm-project
8
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

[docs] Add more complete documentation for -f[no]split-lto-unit

Browse Source 
Option was added in D53891, and only has basic documentation added
later in 5168ddfac4. Add more extensive
documentation with links to related docs.

Differential Revision: https://reviews.llvm.org/D145951
This commit is contained in:
Teresa Johnson 2023-03-13 09:21:01 -07:00
parent b7a33893f5
commit fb3b392264
1 changed files with 18 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
clang/docs/UsersManual.rst
View File

@ -2013,6 +2013,24 @@ are listed below.
devirtualization and virtual constant propagation, for classes with
:doc:`hidden LTO visibility <LTOVisibility>`. Requires ``-flto``.
.. option:: -f[no]split-lto-unit
Controls splitting the :doc:`LTO unit <LTOVisibility>` into regular LTO and
:doc:`ThinLTO` portions, when compiling with -flto=thin. Defaults to false
unless ``-fsanitize=cfi`` or ``-fwhole-program-vtables`` are specified, in
which case it defaults to true. Splitting is required with ``fsanitize=cfi``,
and it is an error to disable via ``-fno-split-lto-unit``. Splitting is
optional with ``-fwhole-program-vtables``, however, it enables more
aggressive whole program vtable optimizations (specifically virtual constant
propagation).
When enabled, vtable definitions and select virtual functions are placed
in the split regular LTO module, enabling more aggressive whole program
vtable optimizations required for CFI and virtual constant propagation.
However, this can increase the LTO link time and memory requirements over
pure ThinLTO, as all split regular LTO modules are merged and LTO linked
with regular LTO.
.. option:: -fforce-emit-vtables
In order to improve devirtualization, forces emitting of vtables even in