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GH-131278: Support building using "computed gotos" for clang-cl on Windows #131279

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Merged
merged 9 commits into from
Mar 17, 2025
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GH-131278: Support building using "computed gotos" for clang-cl on Windows #131279

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98de4c1
Add optimizing flag `WITH_COMPUTED_GOTOS` to support such builds using
chris-eibl Mar 15, 2025
86cb64e
ups - double backticks needed
chris-eibl Mar 15, 2025
3aabeea
Apply suggestions from code review
chris-eibl Mar 15, 2025
ca22c81
remove space before *
chris-eibl Mar 15, 2025
897c527
revert :prog:
chris-eibl Mar 15, 2025
1f5b55f
add whats new
chris-eibl Mar 15, 2025
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Revert "add whats new"
chris-eibl Mar 17, 2025
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apply Steve's suggestion to blurb
chris-eibl Mar 17, 2025
59dac20
fix missing newline in blurb
chris-eibl Mar 17, 2025
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5 changes: 5 additions & 0 deletions Doc/whatsnew/3.14.rst
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Expand Up @@ -1437,6 +1437,11 @@ Build changes
with :c:expr:`Py_NO_LINK_LIB`. (Contributed by Jean-Christophe
Fillion-Robin in :gh:`82909`.)

* building with clang-cl on Windows now supports PGO (profile guided
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Suggested change
* building with clang-cl on Windows now supports PGO (profile guided
* clang-cl builds on Windows now work with ``--pgo`` (profile guided

optimization), uses ``-flto=thin`` and can be configured to use
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optimization), uses ``-flto=thin`` and can be configured to use
optimization), and can be configured to use

Is using -flto=thin important to call out? It shouldn't change the ABI of the build output at all, and it's not configurable.

computed gotos. (Contributed by Chris Eibl in
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IMHO "computed gotos and/or tail calls" would be better here, but up to @Fidget-Spinner 's liking :)

:gh:`130090`, :gh:`131035` and :gh:`131278`).

.. _whatsnew314-pep761:

PEP 761: Discontinuation of PGP signatures
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Build/2025-03-15-12-32-56.gh-issue-131278.1nd0mJ.rst
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@@ -0,0 +1,2 @@
Add optimizing flag ``WITH_COMPUTED_GOTOS`` to support such builds using
clang-cl on Windows. Patch by Chris Eibl.
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Suggested change
Add optimizing flag ``WITH_COMPUTED_GOTOS`` to support such builds using
clang-cl on Windows. Patch by Chris Eibl.
Add optimizing flag ``WITH_COMPUTED_GOTOS`` to Windows builds for when
using a compiler that supports it (currently clang-cl). Patch by Chris Eibl.

1 change: 1 addition & 0 deletions PCbuild/pythoncore.vcxproj
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Expand Up @@ -107,6 +107,7 @@
<PreprocessorDefinitions Condition="'$(UseJIT)' == 'true'">_Py_JIT;%(PreprocessorDefinitions)</PreprocessorDefinitions>
<PreprocessorDefinitions Condition="'$(UseTIER2)' != '' and '$(UseTIER2)' != '0'">_Py_TIER2=$(UseTIER2);%(PreprocessorDefinitions)</PreprocessorDefinitions>
<PreprocessorDefinitions Condition="'$(UseTailCallInterp)' == 'true'">Py_TAIL_CALL_INTERP=1;%(PreprocessorDefinitions)</PreprocessorDefinitions>
<PreprocessorDefinitions Condition="'$(WITH_COMPUTED_GOTOS)' != ''">HAVE_COMPUTED_GOTOS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
</ClCompile>
<Link>
<AdditionalDependencies>version.lib;ws2_32.lib;pathcch.lib;bcrypt.lib;%(AdditionalDependencies)</AdditionalDependencies>
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21 changes: 21 additions & 0 deletions PCbuild/readme.txt
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Expand Up @@ -310,6 +310,27 @@ See
for more on this topic.


Optimization flags
------------------

You can set optimization flags either via

* environment variables, for example:

set WITH_COMPUTED_GOTOS=true

* or pass them as parameters to `build.bat`, for example:

build.bat "/p:WITH_COMPUTED_GOTOS=true"

* or put them in `msbuild.rsp` in the `PCbuild` directory, one flag per line.

Supported flags are:

* WITH_COMPUTED_GOTOS: build the interpreter using "computed gotos".
Currently only supported by clang-cl.


Static library
--------------

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