[lit] Document the undocumented pre-defined substitutions
diff --git a/llvm/docs/CommandGuide/lit.rst b/llvm/docs/CommandGuide/lit.rst
index ff70a21..40aeecd 100644
--- a/llvm/docs/CommandGuide/lit.rst
+++ b/llvm/docs/CommandGuide/lit.rst
@@ -406,17 +406,38 @@
:program:`lit` provides various patterns that can be used with the RUN command.
These are defined in TestRunner.py. The base set of substitutions are:
- ========== ==============
- Macro Substitution
- ========== ==============
- %s source path (path to the file currently being run)
- %S source dir (directory of the file currently being run)
- %p same as %S
- %{pathsep} path separator
- %t temporary file name unique to the test
- %T parent directory of %t (not unique, deprecated, do not use)
- %% %
- ========== ==============
+ ======================= ==============
+ Macro Substitution
+ ======================= ==============
+ %s source path (path to the file currently being run)
+ %S source dir (directory of the file currently being run)
+ %p same as %S
+ %{pathsep} path separator
+ %t temporary file name unique to the test
+ %basename_t The last path component of %t but without the ``.tmp`` extension
+ %T parent directory of %t (not unique, deprecated, do not use)
+ %% %
+ %/s %s but ``\`` is replaced by ``/``
+ %/S %S but ``\`` is replaced by ``/``
+ %/p %p but ``\`` is replaced by ``/``
+ %/t %t but ``\`` is replaced by ``/``
+ %/T %T but ``\`` is replaced by ``/``
+ %{/s:regex_replacement} %/s but escaped for use in the replacement of a ``s@@@`` command in sed
+ %{/S:regex_replacement} %/S but escaped for use in the replacement of a ``s@@@`` command in sed
+ %{/p:regex_replacement} %/p but escaped for use in the replacement of a ``s@@@`` command in sed
+ %{/t:regex_replacement} %/t but escaped for use in the replacement of a ``s@@@`` command in sed
+ %{/T:regex_replacement} %/T but escaped for use in the replacement of a ``s@@@`` command in sed
+ %:s On Windows, %/s but a ``:`` is removed if its the second character.
+ Otherwise, %s but with a single leading ``/`` removed.
+ %:S On Windows, %/S but a ``:`` is removed if its the second character.
+ Otherwise, %S but with a single leading ``/`` removed.
+ %:p On Windows, %/p but a ``:`` is removed if its the second character.
+ Otherwise, %p but with a single leading ``/`` removed.
+ %:t On Windows, %/t but a ``:`` is removed if its the second character.
+ Otherwise, %t but with a single leading ``/`` removed.
+ %:T On Windows, %/T but a ``:`` is removed if its the second character.
+ Otherwise, %T but with a single leading ``/`` removed.
+ ======================= ==============
Other substitutions are provided that are variations on this base set and
further substitution patterns can be defined by each test module. See the