pythonGH-131278: Add option to build with computed gotos on Windows with clang-cl (pythonGH-131279)

Author: chris-eibl

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.

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>

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
 --------------