From 468a7aaeb4dfcd21697dfa46362b9f415b9daf1b Mon Sep 17 00:00:00 2001
From: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>
Date: Mon, 17 Mar 2025 21:32:23 +0100
Subject: GH-131278: Add option to build with computed gotos on Windows with
 clang-cl (GH-131279)

---
 .../2025-03-15-12-32-56.gh-issue-131278.1nd0mJ.rst  |  2 ++
 PCbuild/pythoncore.vcxproj                          |  1 +
 PCbuild/readme.txt                                  | 21 +++++++++++++++++++++
 3 files changed, 24 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Build/2025-03-15-12-32-56.gh-issue-131278.1nd0mJ.rst

diff --git a/Misc/NEWS.d/next/Build/2025-03-15-12-32-56.gh-issue-131278.1nd0mJ.rst b/Misc/NEWS.d/next/Build/2025-03-15-12-32-56.gh-issue-131278.1nd0mJ.rst
new file mode 100644
index 0000000..56e6983
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2025-03-15-12-32-56.gh-issue-131278.1nd0mJ.rst
@@ -0,0 +1,2 @@
+Add optimizing flag ``WITH_COMPUTED_GOTOS`` to Windows builds for when
+using a compiler that supports it (currently clang-cl). Patch by Chris Eibl.
diff --git a/PCbuild/pythoncore.vcxproj b/PCbuild/pythoncore.vcxproj
index 24d0afa..3a06d71 100644
--- a/PCbuild/pythoncore.vcxproj
+++ b/PCbuild/pythoncore.vcxproj
@@ -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>
diff --git a/PCbuild/readme.txt b/PCbuild/readme.txt
index 33952d3..8e82d4e 100644
--- a/PCbuild/readme.txt
+++ b/PCbuild/readme.txt
@@ -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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