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Differential D145951

[docs] Add more complete documentation for -f[no]split-lto-unit
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Authored by tejohnson on Mar 13 2023, 9:25 AM.

Details

Reviewers
nikic
hans
Commits
rGfb3b392264a0: [docs] Add more complete documentation for -f[no]split-lto-unit
Summary

Option was added in D53891, and only has basic documentation added
later in 5168ddfac44206e94f7ddd484d1cf03dee320fa7. Add more extensive
documentation with links to related docs.

Diff Detail

Event Timeline

tejohnson created this revision.Mar 13 2023, 9:25 AM
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tejohnson requested review of this revision.Mar 13 2023, 9:25 AM
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tejohnson mentioned this in D53891: [LTO] Add option to enable LTOUnit splitting, and disable unless needed.Mar 13 2023, 9:26 AM
hans accepted this revision.Mar 13 2023, 10:10 AM

LGTM, thank you!

This revision is now accepted and ready to land.Mar 13 2023, 10:10 AM
This revision was landed with ongoing or failed builds.Mar 13 2023, 11:34 AM
Closed by commit rGfb3b392264a0: [docs] Add more complete documentation for -f[no]split-lto-unit (authored by tejohnson). · Explain Why
This revision was automatically updated to reflect the committed changes.
tejohnson added a commit: rGfb3b392264a0: [docs] Add more complete documentation for -f[no]split-lto-unit.
Harbormaster completed remote builds in B219075: Diff 504708.Mar 13 2023, 12:09 PM
nikic added a comment.Mar 14 2023, 3:12 AM

Thanks!

Revision Contents

PathSize
clang/
docs/
18 lines

Diff 504777

clang/docs/UsersManual.rst

Show First 20 Lines • Show All 2,007 Lines • ▼ Show 20 Lines.. option:: -fstrict-vtable-pointers
still experimental. still experimental.
.. option:: -fwhole-program-vtables .. option:: -fwhole-program-vtables
Enable whole-program vtable optimizations, such as single-implementation Enable whole-program vtable optimizations, such as single-implementation
devirtualization and virtual constant propagation, for classes with devirtualization and virtual constant propagation, for classes with
:doc:`hidden LTO visibility <LTOVisibility>`. Requires ``-flto``. :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 .. option:: -fforce-emit-vtables
In order to improve devirtualization, forces emitting of vtables even in In order to improve devirtualization, forces emitting of vtables even in
modules where it isn't necessary. It causes more inline virtual functions modules where it isn't necessary. It causes more inline virtual functions
to be emitted. to be emitted.
.. option:: -fno-assume-sane-operator-new .. option:: -fno-assume-sane-operator-new
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