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Option was added in D53891 <https://reviews.llvm.org/D53891>, and only has
basic documentation added
later in 5168ddfac44206e94f7ddd484d1cf03dee320fa7. Add more extensive
documentation with links to related docs.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D145951
Files:
clang/docs/UsersManual.rst
Index: clang/docs/UsersManual.rst
===================================================================
--- clang/docs/UsersManual.rst
+++ clang/docs/UsersManual.rst
@@ -2013,6 +2013,24 @@
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
Index: clang/docs/UsersManual.rst
===================================================================
--- clang/docs/UsersManual.rst
+++ clang/docs/UsersManual.rst
@@ -2013,6 +2013,24 @@
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
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