Building the JIT with pre-built stencils

hroncok · November 20, 2025, 12:50pm

Finally, I got back to this. As of now, it seems that I can successfully do:

./configure --enable-experimental-jit=yes-off --enable-optimizations
cp -a .../Python-3.15.0a2-x86_64-optimized-jit_stencils.h jit_stencils-x86_64-unknown-linux-gnu.h
sed -i '/rm -f jit_stencils\*.h/d' Makefile
make ...

And I get a successful build with JIT using pregenerated stencils. No hacks with JIT_DEPS= seem to be necessary. However, I still need to remove this line:

github.com/python/cpython

Makefile.pre.in

v3.15.0a2


      
          	find build -name 'fficonfig.h' -exec rm -f {} ';' || true
          	find build -name '*.py' -exec rm -f {} ';' || true
          	find build -name '*.py[co]' -exec rm -f {} ';' || true
          	-rm -f pybuilddir.txt
          	-rm -f _bootstrap_python
          	-rm -rf web_example python.mjs python.wasm python*.symbols python*.map
          	-rm -f Programs/_testembed Programs/_freeze_module
          	-rm -rf Python/deepfreeze
          	-rm -f Python/frozen_modules/*.h
          	-rm -f Python/frozen_modules/MANIFEST
          	-rm -f jit_stencils*.h
          	-find build -type f -a ! -name '*.gc??' -exec rm -f {} ';'
          	-rm -f Include/pydtrace_probes.h
          	-rm -f profile-gen-stamp
          	-rm -rf Apple/iOS/testbed/Python.xcframework/ios-*/bin
          	-rm -rf Apple/iOS/testbed/Python.xcframework/ios-*/lib
          	-rm -rf Apple/iOS/testbed/Python.xcframework/ios-*/include
          	-rm -rf Apple/iOS/testbed/Python.xcframework/ios-*/Python.framework
          
          .PHONY: profile-removal
          profile-removal:

When I build with --enable-optimizations and don’t remove that line from the clean-retain-profile make target, the build deletes my stencils mid-run and then fails with Can't find clang-21!. I wonder if the stencils need to actually be removed during this task. If they are the same before PGO and after PGO, perhaps not? (Will verify this assumption.)