gh-138497: Support LLVM_VERSION configuration via env

Misc/NEWS.d/next/Build/2025-09-04-12-16-31.gh-issue-138497.Y_5YXh.rst

@@ -0,0 +1,4 @@
+The LLVM version used by the JIT at build time can now be modified using
+the ``LLVM_VERSION`` environment variable. Use this at your own risk, as
+there is only one officially supported LLVM version. For more information,
+please check ``Tools/jit/README.md``.

Tools/jit/README.md

@@ -9,7 +9,7 @@ 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 19 is required. 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 19 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.
 
 It's easy to install all of the required tools:
 

Tools/jit/_llvm.py

@@ -10,8 +10,8 @@
 
 import _targets
 
-_LLVM_VERSION = 19
-_LLVM_VERSION_PATTERN = re.compile(rf"version\s+{_LLVM_VERSION}\.\d+\.\d+\S*\s+")
+
+_LLVM_VERSION = "19"
 _EXTERNALS_LLVM_TAG = "llvm-19.1.7.0"
 
 _P = typing.ParamSpec("_P")
@@ -56,53 +56,66 @@ async def _run(tool: str, args: typing.Iterable[str], echo: bool = False) -> str
 
 
 @_async_cache
-async def _check_tool_version(name: str, *, echo: bool = False) -> bool:
+async def _check_tool_version(
+ name: str, llvm_version: str, *, echo: bool = False
+) -> bool:
  output = await _run(name, ["--version"], echo=echo)
- return bool(output and _LLVM_VERSION_PATTERN.search(output))
+ _llvm_version_pattern = re.compile(rf"version\s+{llvm_version}\.\d+\.\d+\S*\s+")
+ return bool(output and _llvm_version_pattern.search(output))
 
 
 @_async_cache
-async def _get_brew_llvm_prefix(*, echo: bool = False) -> str | None:
- output = await _run("brew", ["--prefix", f"llvm@{_LLVM_VERSION}"], echo=echo)
+async def _get_brew_llvm_prefix(llvm_version: str, *, echo: bool = False) -> str | None:
+ output = await _run("brew", ["--prefix", f"llvm@{llvm_version}"], echo=echo)
  return output and output.removesuffix("\n")
 
 
 @_async_cache
-async def _find_tool(tool: str, *, echo: bool = False) -> str | None:
+async def _find_tool(tool: str, llvm_version: str, *, echo: bool = False) -> str | None:
  # Unversioned executables:
  path = tool
- if await _check_tool_version(path, echo=echo):
+ if await _check_tool_version(path, llvm_version, echo=echo):
  return path
  # Versioned executables:
- path = f"{tool}-{_LLVM_VERSION}"
- if await _check_tool_version(path, echo=echo):
+ path = f"{tool}-{llvm_version}"
+ if await _check_tool_version(path, llvm_version, echo=echo):
  return path
  # PCbuild externals:
  externals = os.environ.get("EXTERNALS_DIR", _targets.EXTERNALS)
  path = os.path.join(externals, _EXTERNALS_LLVM_TAG, "bin", tool)
- if await _check_tool_version(path, echo=echo):
+ if await _check_tool_version(path, llvm_version, echo=echo):
  return path
  # Homebrew-installed executables:
- prefix = await _get_brew_llvm_prefix(echo=echo)
+ prefix = await _get_brew_llvm_prefix(llvm_version, echo=echo)
  if prefix is not None:
  path = os.path.join(prefix, "bin", tool)
- if await _check_tool_version(path, echo=echo):
+ if await _check_tool_version(path, llvm_version, echo=echo):
  return path
  # Nothing found:
  return None
 
 
 async def maybe_run(
- tool: str, args: typing.Iterable[str], echo: bool = False
+ tool: str,
+ args: typing.Iterable[str],
+ echo: bool = False,
+ llvm_version: str = _LLVM_VERSION,
 ) -> str | None:
  """Run an LLVM tool if it can be found. Otherwise, return None."""
- path = await _find_tool(tool, echo=echo)
+
+ path = await _find_tool(tool, llvm_version, echo=echo)
  return path and await _run(path, args, echo=echo)
 
 
-async def run(tool: str, args: typing.Iterable[str], echo: bool = False) -> str:
+async def run(
+ tool: str,
+ args: typing.Iterable[str],
+ echo: bool = False,
+ llvm_version: str = _LLVM_VERSION,
+) -> str:
  """Run an LLVM tool if it can be found. Otherwise, raise RuntimeError."""
- output = await maybe_run(tool, args, echo=echo)
+
+ output = await maybe_run(tool, args, echo=echo, llvm_version=llvm_version)
  if output is None:
- raise RuntimeError(f"Can't find{tool}-{_LLVM_VERSION}!")
+ raise RuntimeError(f"Can't find{tool}-{llvm_version}!")
  return output

Tools/jit/_targets.py

@@ -50,6 +50,7 @@ class _Target(typing.Generic[_S, _R]):
  debug: bool = False
  verbose: bool = False
  cflags: str = ""
+ llvm_version: str = _llvm._LLVM_VERSION
  known_symbols: dict[str, int] = dataclasses.field(default_factory=dict)
  pyconfig_dir: pathlib.Path = pathlib.Path.cwd().resolve()
 
@@ -81,7 +82,9 @@ def _compute_digest(self) -> str:
  async def _parse(self, path: pathlib.Path) -> _stencils.StencilGroup:
  group = _stencils.StencilGroup()
  args = ["--disassemble", "--reloc", f"{path}"]
- output = await _llvm.maybe_run("llvm-objdump", args, echo=self.verbose)
+ output = await _llvm.maybe_run(
+ "llvm-objdump", args, echo=self.verbose, llvm_version=self.llvm_version
+ )
  if output is not None:
  # Make sure that full paths don't leak out (for reproducibility):
  long, short = str(path), str(path.name)
@@ -99,7 +102,9 @@ async def _parse(self, path: pathlib.Path) -> _stencils.StencilGroup:
  "--sections",
  f"{path}",
  ]
- output = await _llvm.run("llvm-readobj", args, echo=self.verbose)
+ output = await _llvm.run(
+ "llvm-readobj", args, echo=self.verbose, llvm_version=self.llvm_version
+ )
  # --elf-output-style=JSON is only *slightly* broken on Mach-O...
  output = output.replace("PrivateExtern\n", "\n")
  output = output.replace("Extern\n", "\n")
@@ -175,12 +180,16 @@ async def _compile(
  # Allow user-provided CFLAGS to override any defaults
  *shlex.split(self.cflags),
  ]
- await _llvm.run("clang", args_s, echo=self.verbose)
+ await _llvm.run(
+ "clang", args_s, echo=self.verbose, llvm_version=self.llvm_version
+ )
  self.optimizer(
  s, label_prefix=self.label_prefix, symbol_prefix=self.symbol_prefix
  ).run()
  args_o = [f"--target={self.triple}", "-c", "-o", f"{o}", f"{s}"]
- await _llvm.run("clang", args_o, echo=self.verbose)
+ await _llvm.run(
+ "clang", args_o, echo=self.verbose, llvm_version=self.llvm_version
+ )
  return await self._parse(o)
 
  async def _build_stencils(self) -> dict[str, _stencils.StencilGroup]:
@@ -224,6 +233,8 @@ def build(
  if not self.stable:
  warning = f"JIT support for{self.triple} is still experimental!"
  request = "Please report any issues you encounter.".center(len(warning))
+ if self.llvm_version != _llvm._LLVM_VERSION:
+ request = f"Warning! Building with an LLVM version other than{_llvm._LLVM_VERSION} is not supported."
  outline = "=" * len(warning)
  print("\n".join(["", outline, warning, request, outline, ""]))
  digest = f"//{self._compute_digest()}\n"

Tools/jit/build.py

@@ -42,13 +42,16 @@
  parser.add_argument(
  "--cflags", help="additional flags to pass to the compiler", default=""
  )
+ parser.add_argument("--llvm-version", help="LLVM version to use")
  args = parser.parse_args()
  for target in args.target:
  target.debug = args.debug
  target.force = args.force
  target.verbose = args.verbose
  target.cflags = args.cflags
  target.pyconfig_dir = args.pyconfig_dir
+ if args.llvm_version:
+ target.llvm_version = args.llvm_version
  target.build(
  comment=comment,
  force=args.force,

configure.ac

@@ -2786,7 +2786,7 @@ AS_VAR_IF([jit_flags],
  [],
  [AS_VAR_APPEND([CFLAGS_NODIST], [" $jit_flags"])
  AS_VAR_SET([REGEN_JIT_COMMAND],
- ["\$(PYTHON_FOR_REGEN) \$(srcdir)/Tools/jit/build.py ${ARCH_TRIPLES:-$host} --output-dir . --pyconfig-dir . --cflags=\"$CFLAGS_JIT\""])
+ ["\$(PYTHON_FOR_REGEN) \$(srcdir)/Tools/jit/build.py ${ARCH_TRIPLES:-$host} --output-dir . --pyconfig-dir . --cflags=\"$CFLAGS_JIT\" --llvm-version=\"$LLVM_VERSION\""])
  AS_VAR_IF([Py_DEBUG],
  [true],
  [AS_VAR_APPEND([REGEN_JIT_COMMAND], [" --debug"])],