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Clarify documentation for -funique-source-file-names. #135832

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merged 2 commits into from
Apr 15, 2025
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Clarify documentation for -funique-source-file-names. #135832

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[𝘀𝗽𝗿] initial version
pcc Apr 15, 2025
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pcc Apr 15, 2025
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26 changes: 23 additions & 3 deletions clang/docs/UsersManual.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -2301,11 +2301,31 @@ are listed below.

When enabled, allows the compiler to assume that each object file
passed to the linker has been compiled using a unique source file
name. This is useful for reducing link times when doing ThinLTO
path. This is useful for reducing link times when doing ThinLTO
in combination with whole-program devirtualization or CFI.

A misuse of this flag will generally result in a duplicate symbol
error at link time.
The full source path passed to the compiler must be unique. This
means that, for example, the following is a usage error:

.. code-block:: console

$ cd foo
$ clang -funique-source-file-names -c foo.c
$ cd ../bar
$ clang -funique-source-file-names -c foo.c
$ cd ..
$ clang foo/foo.o bar/foo.o

but this is not:

.. code-block:: console

$ clang -funique-source-file-names -c foo/foo.c
$ clang -funique-source-file-names -c bar/foo.c
$ clang foo/foo.o bar/foo.o

A misuse of this flag will generally either be harmless or result
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@teresajohnson teresajohnson Apr 15, 2025

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I'd prefer to remove the harmless comment as it would be good to discourage uses that violate the intent. So maybe just "may result in a duplicate ..." ?

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@pcc pcc Apr 15, 2025

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Done

in a duplicate symbol error at link time.

.. option:: -fforce-emit-vtables

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