GH-113464: Get LLVM from cpython-bin-deps on Windows (GH-133278)

Tools/jit/README.md

@@ -41,7 +41,9 @@ Homebrew won't add any of the tools to your `$PATH`. That's okay; the build scri
 
 ### Windows
 
-Install LLVM 19 [by searching for it on LLVM's GitHub releases page](https://github.com/llvm/llvm-project/releases?q=19), 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".**
+LLVM is downloaded automatically (along with other external binary dependencies) by `PCbuild\build.bat`.
+
+Otherwise, you can install LLVM 19 [by searching for it on LLVM's GitHub releases page](https://github.com/llvm/llvm-project/releases?q=19), 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):
 

Tools/jit/_llvm.py

@@ -8,8 +8,11 @@ import shlex
 import subprocess
 import typing
 
+import _targets
+
 _LLVM_VERSION = 19
 _LLVM_VERSION_PATTERN = re.compile(rf"version\s+{_LLVM_VERSION}\.\d+\.\d+\S*\s+")
+_EXTERNALS_LLVM_TAG = "llvm-19.1.7.0"
 
 _P = typing.ParamSpec("_P")
 _R = typing.TypeVar("_R")
@@ -72,6 +75,11 @@ async def _find_tool(tool: str, *, echo: bool = False) -> str | None:
         return path
     # Versioned executables:
     path = f"{tool}-{_LLVM_VERSION}"
+    if await _check_tool_version(path, 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):
         return path
     # Homebrew-installed executables:

Tools/jit/_targets.py

@@ -23,8 +23,10 @@ TOOLS_JIT_BUILD = pathlib.Path(__file__).resolve()
 TOOLS_JIT = TOOLS_JIT_BUILD.parent
 TOOLS = TOOLS_JIT.parent
 CPYTHON = TOOLS.parent
+EXTERNALS = CPYTHON / "externals"
 PYTHON_EXECUTOR_CASES_C_H = CPYTHON / "Python" / "executor_cases.c.h"
 TOOLS_JIT_TEMPLATE_C = TOOLS_JIT / "template.c"
+
 ASYNCIO_RUNNER = asyncio.Runner()
 
 _S = typing.TypeVar("_S", _schema.COFFSection, _schema.ELFSection, _schema.MachOSection)

Tools/jit/build.py

@@ -8,6 +8,7 @@ import sys
 import _targets
 
 if __name__ == "__main__":
+    out = pathlib.Path.cwd().resolve()
     comment = f"$ {shlex.join([pathlib.Path(sys.executable).name] + sys.argv)}"
     parser = argparse.ArgumentParser(description=__doc__)
     parser.add_argument(
@@ -31,17 +32,22 @@ if __name__ == "__main__":
         target.force = args.force
         target.verbose = args.verbose
         target.build(
-            pathlib.Path.cwd(),
+            out,
             comment=comment,
             stencils_h=f"jit_stencils-{target.triple}.h",
             force=args.force,
         )
-
-    with open("jit_stencils.h", "w") as fp:
-        for idx, target in enumerate(args.target):
-            fp.write(f"#{'if' if idx == 0 else 'elif'} {target.condition}\n")
-            fp.write(f'#include "jit_stencils-{target.triple}.h"\n')
-
-        fp.write("#else\n")
-        fp.write('#error "unexpected target"\n')
-        fp.write("#endif\n")
+    jit_stencils_h = out / "jit_stencils.h"
+    lines = [f"// {comment}\n"]
+    guard = "#if"
+    for target in args.target:
+        lines.append(f"{guard} {target.condition}\n")
+        lines.append(f'#include "jit_stencils-{target.triple}.h"\n')
+        guard = "#elif"
+    lines.append("#else\n")
+    lines.append('#error "unexpected target"\n')
+    lines.append("#endif\n")
+    body = "".join(lines)
+    # Don't touch the file if it hasn't changed (so we don't trigger a rebuild):
+    if not jit_stencils_h.is_file() or jit_stencils_h.read_text() != body:
+        jit_stencils_h.write_text(body)