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[clang][docs] Update doc and release note for probe instrumentation #162606

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[clang][docs] Update doc and release note for probe instrumentation #162606

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38 changes: 38 additions & 0 deletions clang/docs/UsersManual.rst
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Expand Up @@ -2780,6 +2780,25 @@ usual build cycle when using sample profilers for optimization:
/clang:-fdebug-info-for-profiling /clang:-funique-internal-linkage-names ^
code.cc /Fe:code /fuse-ld=lld /link /debug:dwarf

[OPTIONAL] Pseudo instrumentation can be used as the anchor for accurate
profile mapping with the ``-fpseudo-probe-for-profiling`` option.
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@MaskRay MaskRay Oct 9, 2025 •
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Mention the relation with -fdebug-info-for-profiling. Can both be used together?

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@HaohaiWen HaohaiWen Oct 10, 2025 •
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-fdebug-info-for-profiling enables discriminator in debug info which is not used when using pseudo probe.
They can be used together if user want to generate probe based profile file and line/discriminator based profile file with same binary. e.g. https://github.com/llvm/llvm-project/blob/main/llvm/test/tools/llvm-profgen/coff-profile.test


On Linux:

.. code-block:: console

$ clang++ -O2 -gline-tables-only \
-fpseudo-probe-for-profiling -funique-internal-linkage-names \
code.cc -o code

On Windows:

.. code-block:: winbatch

> clang-cl /O2 -gdwarf -gline-tables-only ^
-fpseudo-probe-for-profiling /clang:-funique-internal-linkage-names ^
code.cc /Fe:code -fuse-ld=lld /link /debug:dwarf

.. note::

:ref:`-funique-internal-linkage-names <funique_internal_linkage_names>`
Expand Down Expand Up @@ -2879,6 +2898,25 @@ usual build cycle when using sample profilers for optimization:
/clang:-fdebug-info-for-profiling /clang:-funique-internal-linkage-names ^
-fprofile-sample-use=code.prof code.cc /Fe:code -fuse-ld=lld /link /debug:dwarf

[OPTIONAL] Pseudo instrumentation can be used as the anchor for accurate
profile mapping with the ``-fpseudo-probe-for-profiling`` option.

On Linux:

.. code-block:: console

$ clang++ -O2 \
-fpseudo-probe-for-profiling -funique-internal-linkage-names \
-fprofile-sample-use=code.prof code.cc -o code

On Windows:

.. code-block:: winbatch

> clang-cl /O2 ^
-fpseudo-probe-for-profiling /clang:-funique-internal-linkage-names ^
-fprofile-sample-use=code.prof code.cc /Fe:code

[OPTIONAL] Sampling-based profiles can have inaccuracies or missing block/
edge counters. The profile inference algorithm (profi) can be used to infer
missing blocks and edge counts, and improve the quality of profile data.
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4 changes: 4 additions & 0 deletions llvm/docs/ReleaseNotes.md
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Expand Up @@ -134,6 +134,8 @@ Changes to the WebAssembly Backend
Changes to the Windows Target
-----------------------------

* `-fpseudo-probe-for-profiling` is now supported for COFF.

Changes to the X86 Backend
--------------------------

Expand All @@ -160,6 +162,8 @@ Changes to the Debug Info
Changes to the LLVM tools
---------------------------------

* `llvm-profgen` now supports decoding pseudo probe for COFF binaries.

* `llvm-readelf` now dumps all hex format values in lower-case mode.
* Some code paths for supporting Python 2.7 in `llvm-lit` have been removed.
* Support for `%T` in lit has been removed.
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