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GH-125498: Update JIT builds to use LLVM 19 and preserve_none (GH-125499)

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This commit is contained in:
Savannah Ostrowski
2024-10-30 12:03:31 -07:00
committed by GitHub
parent 597d814334
commit c29bbe2101
11 changed files with 69 additions and 78 deletions
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21
Tools/jit/README.md
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@@ -7,49 +7,46 @@ This version of CPython can be built with an experimental just-in-time compiler[
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 18 is required. Both `clang` and `llvm-readobj` need to be installed and discoverable (version suffixes, like `clang-18`, 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 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.
It's easy to install all of the required tools:
### Linux
Install LLVM 18 on Ubuntu/Debian:
Install LLVM 19 on Ubuntu/Debian:
```sh
wget https://apt.llvm.org/llvm.sh
chmod +x llvm.sh
sudo ./llvm.sh 18
sudo ./llvm.sh 19
```
Install LLVM 18 on Fedora Linux 40 or newer:
Install LLVM 19 on Fedora Linux 40 or newer:
```sh
sudo dnf install 'clang(major) = 18' 'llvm(major) = 18'
sudo dnf install 'clang(major) = 19' 'llvm(major) = 19'
```
### macOS
Install LLVM 18 with [Homebrew](https://brew.sh):
Install LLVM 19 with [Homebrew](https://brew.sh):
```sh
brew install llvm@18
brew install llvm@19
```
Homebrew won't add any of the tools to your `$PATH`. That's okay; the build script knows how to find them.
### Windows
Install LLVM 18 [by searching for it on LLVM's GitHub releases page](https://github.com/llvm/llvm-project/releases?q=18), 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".**
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):
```sh
choco install llvm --version=18.1.6
choco install llvm --version=19.1.0
```
### Dev Containers
If you are working 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 40 base image includes LLVM 18 out of the box.
## Building

2
Tools/jit/_llvm.py
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@@ -8,7 +8,7 @@ import shlex
import subprocess
import typing
_LLVM_VERSION = 18
_LLVM_VERSION = 19
_LLVM_VERSION_PATTERN = re.compile(rf"version\s+{_LLVM_VERSION}\.\d+\.\d+\S*\s+")
_P = typing.ParamSpec("_P")

14
Tools/jit/_stencils.py
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@@ -2,6 +2,7 @@
import dataclasses
import enum
import sys
import typing
import _schema
@@ -132,8 +133,18 @@ class Hole:
def __post_init__(self) -> None:
self.func = _PATCH_FUNCS[self.kind]
def fold(self, other: typing.Self) -> typing.Self | None:
def fold(self, other: typing.Self, body: bytes) -> typing.Self | None:
"""Combine two holes into a single hole, if possible."""
instruction_a = int.from_bytes(
body[self.offset : self.offset + 4], byteorder=sys.byteorder
)
instruction_b = int.from_bytes(
body[other.offset : other.offset + 4], byteorder=sys.byteorder
)
reg_a = instruction_a & 0b11111
reg_b1 = instruction_b & 0b11111
reg_b2 = (instruction_b >> 5) & 0b11111
if (
self.offset + 4 == other.offset
and self.value == other.value
@@ -141,6 +152,7 @@ class Hole:
and self.addend == other.addend
and self.func == "patch_aarch64_21rx"
and other.func == "patch_aarch64_12x"
and reg_a == reg_b1 == reg_b2
):
# These can *only* be properly relaxed when they appear together and
# patch the same value:

67
Tools/jit/_targets.py
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@@ -26,7 +26,6 @@ CPYTHON = TOOLS.parent
PYTHON_EXECUTOR_CASES_C_H = CPYTHON / "Python" / "executor_cases.c.h"
TOOLS_JIT_TEMPLATE_C = TOOLS_JIT / "template.c"
_S = typing.TypeVar("_S", _schema.COFFSection, _schema.ELFSection, _schema.MachOSection)
_R = typing.TypeVar(
"_R", _schema.COFFRelocation, _schema.ELFRelocation, _schema.MachORelocation
@@ -39,7 +38,6 @@ class _Target(typing.Generic[_S, _R]):
_: dataclasses.KW_ONLY
alignment: int = 1
args: typing.Sequence[str] = ()
ghccc: bool = False
prefix: str = ""
stable: bool = False
debug: bool = False
@@ -88,11 +86,7 @@ class _Target(typing.Generic[_S, _R]):
sections: list[dict[typing.Literal["Section"], _S]] = json.loads(output)
for wrapped_section in sections:
self._handle_section(wrapped_section["Section"], group)
# The trampoline's entry point is just named "_ENTRY", since on some
# platforms we later assume that any function starting with "_JIT_" uses
# the GHC calling convention:
entry_symbol = "_JIT_ENTRY" if "_JIT_ENTRY" in group.symbols else "_ENTRY"
assert group.symbols[entry_symbol] == (_stencils.HoleValue.CODE, 0)
assert group.symbols["_JIT_ENTRY"] == (_stencils.HoleValue.CODE, 0)
if group.data.body:
line = f"0: {str(bytes(group.data.body)).removeprefix('b')}"
group.data.disassembly.append(line)
@@ -112,9 +106,6 @@ class _Target(typing.Generic[_S, _R]):
async def _compile(
self, opname: str, c: pathlib.Path, tempdir: pathlib.Path
) -> _stencils.StencilGroup:
# "Compile" the trampoline to an empty stencil group if it's not needed:
if opname == "trampoline" and not self.ghccc:
return _stencils.StencilGroup()
o = tempdir / f"{opname}.o"
args = [
f"--target={self.triple}",
@@ -128,6 +119,7 @@ class _Target(typing.Generic[_S, _R]):
f"-I{CPYTHON / 'Include' / 'internal'}",
f"-I{CPYTHON / 'Include' / 'internal' / 'mimalloc'}",
f"-I{CPYTHON / 'Python'}",
f"-I{CPYTHON / 'Tools' / 'jit'}",
"-O3",
"-c",
# This debug info isn't necessary, and bloats out the JIT'ed code.
@@ -143,44 +135,12 @@ class _Target(typing.Generic[_S, _R]):
# Don't call stack-smashing canaries that we can't find or patch:
"-fno-stack-protector",
"-std=c11",
"-o",
f"{o}",
f"{c}",
*self.args,
]
if self.ghccc:
# This is a bit of an ugly workaround, but it makes the code much
# smaller and faster, so it's worth it. We want to use the GHC
# calling convention, but Clang doesn't support it. So, we *first*
# compile the code to LLVM IR, perform some text replacements on the
# IR to change the calling convention(!), and then compile *that*.
# Once we have access to Clang 19, we can get rid of this and use
# __attribute__((preserve_none)) directly in the C code instead:
ll = tempdir / f"{opname}.ll"
args_ll = args + [
# -fomit-frame-pointer is necessary because the GHC calling
# convention uses RBP to pass arguments:
"-S",
"-emit-llvm",
"-fomit-frame-pointer",
"-o",
f"{ll}",
f"{c}",
]
await _llvm.run("clang", args_ll, echo=self.verbose)
ir = ll.read_text()
# This handles declarations, definitions, and calls to named symbols
# starting with "_JIT_":
ir = re.sub(
r"(((noalias|nonnull|noundef) )*ptr @_JIT_\w+\()", r"ghccc \1", ir
)
# This handles calls to anonymous callees, since anything with
# "musttail" needs to use the same calling convention:
ir = ir.replace("musttail call", "musttail call ghccc")
# Sometimes *both* replacements happen at the same site, so fix it:
ir = ir.replace("ghccc ghccc", "ghccc")
ll.write_text(ir)
args_o = args + ["-Wno-unused-command-line-argument", "-o", f"{o}", f"{ll}"]
else:
args_o = args + ["-o", f"{o}", f"{c}"]
await _llvm.run("clang", args_o, echo=self.verbose)
await _llvm.run("clang", args, echo=self.verbose)
return await self._parse(o)
async def _build_stencils(self) -> dict[str, _stencils.StencilGroup]:
@@ -519,7 +479,6 @@ class _MachO(
def get_target(host: str) -> _COFF | _ELF | _MachO:
"""Build a _Target for the given host "triple" and options."""
# ghccc currently crashes Clang when combined with musttail on aarch64. :(
target: _COFF | _ELF | _MachO
if re.fullmatch(r"aarch64-apple-darwin.*", host):
target = _MachO(host, alignment=8, prefix="_")
@@ -535,16 +494,20 @@ def get_target(host: str) -> _COFF | _ELF | _MachO:
]
target = _ELF(host, alignment=8, args=args)
elif re.fullmatch(r"i686-pc-windows-msvc", host):
args = ["-DPy_NO_ENABLE_SHARED"]
target = _COFF(host, args=args, ghccc=True, prefix="_")
args = [
"-DPy_NO_ENABLE_SHARED",
# __attribute__((preserve_none)) is not supported
"-Wno-ignored-attributes",
]
target = _COFF(host, args=args, prefix="_")
elif re.fullmatch(r"x86_64-apple-darwin.*", host):
target = _MachO(host, ghccc=True, prefix="_")
target = _MachO(host, prefix="_")
elif re.fullmatch(r"x86_64-pc-windows-msvc", host):
args = ["-fms-runtime-lib=dll"]
target = _COFF(host, args=args, ghccc=True)
target = _COFF(host, args=args)
elif re.fullmatch(r"x86_64-.*-linux-gnu", host):
args = ["-fpic"]
target = _ELF(host, args=args, ghccc=True)
target = _ELF(host, args=args)
else:
raise ValueError(host)
return target

2
Tools/jit/_writer.py
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@@ -65,7 +65,7 @@ def _dump_stencil(opname: str, group: _stencils.StencilGroup) -> typing.Iterator
if skip:
skip = False
continue
if pair and (folded := hole.fold(pair)):
if pair and (folded := hole.fold(pair, stencil.body)):
skip = True
hole = folded
yield f" {hole.as_c(part)}"

4
Tools/jit/jit.h Normal file
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@@ -0,0 +1,4 @@
// To use preserve_none in JIT builds, we need to declare a separate function
// pointer with __attribute__((preserve_none)), since this attribute may not be
// supported by the compiler used to build the rest of the interpreter.
typedef jit_func __attribute__((preserve_none)) jit_func_preserve_none;

8
Tools/jit/template.c
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@@ -21,6 +21,8 @@
#include "ceval_macros.h"
#include "jit.h"
#undef CURRENT_OPARG
#define CURRENT_OPARG() (_oparg)
@@ -49,7 +51,7 @@
do { \
OPT_STAT_INC(traces_executed); \
__attribute__((musttail)) \
return ((jit_func)((EXECUTOR)->jit_side_entry))(frame, stack_pointer, tstate); \
return ((jit_func_preserve_none)((EXECUTOR)->jit_side_entry))(frame, stack_pointer, tstate); \
} while (0)
#undef GOTO_TIER_ONE
@@ -72,7 +74,7 @@ do { \
do { \
PyAPI_DATA(void) ALIAS; \
__attribute__((musttail)) \
return ((jit_func)&ALIAS)(frame, stack_pointer, tstate); \
return ((jit_func_preserve_none)&ALIAS)(frame, stack_pointer, tstate); \
} while (0)
#undef JUMP_TO_JUMP_TARGET
@@ -86,7 +88,7 @@ do { \
#define TIER_TWO 2
_Py_CODEUNIT *
__attribute__((preserve_none)) _Py_CODEUNIT *
_JIT_ENTRY(_PyInterpreterFrame *frame, _PyStackRef *stack_pointer, PyThreadState *tstate)
{
// Locals that the instruction implementations expect to exist:

9
Tools/jit/trampoline.c
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@@ -4,11 +4,10 @@
#include "pycore_frame.h"
#include "pycore_jit.h"
// This is where the calling convention changes, on platforms that require it.
// The actual change is patched in while the JIT compiler is being built, in
// Tools/jit/_targets.py. On other platforms, this function compiles to nothing.
#include "jit.h"
_Py_CODEUNIT *
_ENTRY(_PyInterpreterFrame *frame, _PyStackRef *stack_pointer, PyThreadState *tstate)
_JIT_ENTRY(_PyInterpreterFrame *frame, _PyStackRef *stack_pointer, PyThreadState *tstate)
{
// This is subtle. The actual trace will return to us once it exits, so we
// need to make sure that we stay alive until then. If our trace side-exits
@@ -19,7 +18,7 @@ _ENTRY(_PyInterpreterFrame *frame, _PyStackRef *stack_pointer, PyThreadState *ts
Py_INCREF(executor);
// Note that this is *not* a tail call:
PyAPI_DATA(void) _JIT_CONTINUE;
_Py_CODEUNIT *target = ((jit_func)&_JIT_CONTINUE)(frame, stack_pointer, tstate);
_Py_CODEUNIT *target = ((jit_func_preserve_none)&_JIT_CONTINUE)(frame, stack_pointer, tstate);
Py_SETREF(tstate->previous_executor, executor);
return target;
}