GH-136895: Update JIT builds to use LLVM 21

mcepl · mcepl · commit b6c50f4bc0e8 · 2026-03-25T14:37:40.000+01:00
Bump the JIT toolchain from LLVM 20 to LLVM 21 (21.1.8). Updated
across CI workflows, build scripts, documentation, and the externals
tag.
diff --git a/.github/workflows/jit.yml b/.github/workflows/jit.yml
@@ -21,7 +21,7 @@ concurrency:
 
 env:
   FORCE_COLOR: 1
-  LLVM_VERSION: 20
+  LLVM_VERSION: 21
 
 jobs:
   interpreter:
diff --git a/.github/workflows/tail-call.yml b/.github/workflows/tail-call.yml
@@ -20,7 +20,7 @@ concurrency:
 
 env:
   FORCE_COLOR: 1
-  LLVM_VERSION: 20
+  LLVM_VERSION: 21
 
 jobs:
   windows:
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-10-19-10-32-28.gh-issue-136895.HfsEh0.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-10-19-10-32-28.gh-issue-136895.HfsEh0.rst
@@ -1 +1 @@
-Update JIT compilation to use LLVM 20 at build time.
+Update JIT compilation to use LLVM 21 at build time.
diff --git a/PCbuild/get_externals.bat b/PCbuild/get_externals.bat
@@ -82,7 +82,7 @@ if NOT "%IncludeLibffi%"=="false"  set binaries=%binaries% libffi-3.4.4
 if NOT "%IncludeSSL%"=="false"     set binaries=%binaries% openssl-bin-3.0.19
 if NOT "%IncludeTkinter%"=="false" set binaries=%binaries% tcltk-8.6.15.0
 if NOT "%IncludeSSLSrc%"=="false"  set binaries=%binaries% nasm-2.11.06
-if NOT "%IncludeLLVM%"=="false"    set binaries=%binaries% llvm-20.1.8.0
+if NOT "%IncludeLLVM%"=="false"    set binaries=%binaries% llvm-21.1.8.0
 
 for %%b in (%binaries%) do (
     if exist "%EXTERNALS_DIR%\%%b" (
diff --git a/Python/jit.c b/Python/jit.c
@@ -428,7 +428,7 @@ void patch_x86_64_trampoline(unsigned char *location, int ordinal, jit_state *st
     #define DATA_ALIGN 8
 #elif defined(__x86_64__) || defined(_M_X64)
     // x86_64 trampolines: 14 bytes (jmp *(%rip) + 8-byte addr) + 2 bytes padding.
-    // Currently used on macOS where LLVM 20 GOT entries may exceed &plusmn;2GB
+    // Currently used on macOS where LLVM 21 GOT entries may exceed &plusmn;2GB
     // PC-relative range, but enabled on all x86_64 platforms defensively.
     #define TRAMPOLINE_SIZE 16
     #define DATA_ALIGN 8
diff --git a/Tools/jit/README.md b/Tools/jit/README.md
@@ -9,32 +9,32 @@ Python 3.11 or newer is required to build the JIT.
 
 The JIT compiler does not require end users to install any third-party dependencies, but part of it must be *built* using LLVM[^why-llvm]. You are *not* required to build the rest of CPython using LLVM, or even the same version of LLVM (in fact, this is uncommon).
 
-LLVM version 20 is the officially supported version. You can modify if needed using the `LLVM_VERSION` env var during configure. Both `clang` and `llvm-readobj` need to be installed and discoverable (version suffixes, like `clang-19`, are okay). It's highly recommended that you also have `llvm-objdump` available, since this allows the build script to dump human-readable assembly for the generated code.
+LLVM version 21 is the officially supported version. You can modify if needed using the `LLVM_VERSION` env var during configure. Both `clang` and `llvm-readobj` need to be installed and discoverable (version suffixes, like `clang-21`, are okay). It's highly recommended that you also have `llvm-objdump` available, since this allows the build script to dump human-readable assembly for the generated code.
 
 It's easy to install all of the required tools:
 
 ### Linux
 
-Install LLVM 20 on Ubuntu/Debian:
+Install LLVM 21 on Ubuntu/Debian:
 
 ```sh
 wget https://apt.llvm.org/llvm.sh
 chmod +x llvm.sh
-sudo ./llvm.sh 20
+sudo ./llvm.sh 21
 ```
 
-Install LLVM 20 on Fedora Linux 40 or newer:
+Install LLVM 21 on Fedora Linux 40 or newer:
 
 ```sh
-sudo dnf install 'clang(major) = 20' 'llvm(major) = 20'
+sudo dnf install 'clang(major) = 21' 'llvm(major) = 21'
 ```
 
 ### macOS
 
-Install LLVM 20 with [Homebrew](https://brew.sh):
+Install LLVM 21 with [Homebrew](https://brew.sh):
 
 ```sh
-brew install llvm@20
+brew install llvm@21
 ```
 
 Homebrew won't add any of the tools to your `$PATH`. That's okay; the build script knows how to find them.
@@ -43,18 +43,18 @@ Homebrew won't add any of the tools to your `$PATH`. That's okay; the build scri
 
 LLVM is downloaded automatically (along with other external binary dependencies) by `PCbuild\build.bat`.
 
-Otherwise, you can install LLVM 20 [by searching for it on LLVM's GitHub releases page](https://github.com/llvm/llvm-project/releases?q=20), clicking on "Assets", downloading the appropriate Windows installer for your platform (likely the file ending with `-win64.exe`), and running it. **When installing, be sure to select the option labeled "Add LLVM to the system PATH".**
+Otherwise, you can install LLVM 21 [by searching for it on LLVM's GitHub releases page](https://github.com/llvm/llvm-project/releases?q=21), clicking on "Assets", downloading the appropriate Windows installer for your platform (likely the file ending with `-win64.exe`), and running it. **When installing, be sure to select the option labeled "Add LLVM to the system PATH".**
 
 Alternatively, you can use [chocolatey](https://chocolatey.org):
 
 ```sh
-choco install llvm --version=20.1.8
+choco install llvm --version=21.1.8
 ```
 
 ### Dev Containers
 
 If you are working on CPython in a [Codespaces instance](https://devguide.python.org/getting-started/setup-building/#using-codespaces), there's no
-need to install LLVM as the Fedora 42 base image includes LLVM 20 out of the box.
+need to install LLVM as the Fedora 42 base image includes LLVM 21 out of the box.
 
 ## Building
 
diff --git a/Tools/jit/_llvm.py b/Tools/jit/_llvm.py
@@ -10,9 +10,9 @@
 
 import _targets
 
-_LLVM_VERSION = 20
+_LLVM_VERSION = 21
 _LLVM_VERSION_PATTERN = re.compile(rf"version\s+{_LLVM_VERSION}\.\d+\.\d+\S*\s+")
-_EXTERNALS_LLVM_TAG = "llvm-20.1.8.0"
+_EXTERNALS_LLVM_TAG = "llvm-21.1.8.0"
 
 _P = typing.ParamSpec("_P")
 _R = typing.TypeVar("_R")

Original file line number	Diff line number	Diff line change
`@@ -1 +1 @@`
`1`		`-Update JIT compilation to use LLVM 20 at build time.`
	`1`	`+Update JIT compilation to use LLVM 21 at build time.`