https://github.com/python/cpython/commit/ea0453ee979174d6fc14aae0fd85e4ede6742a86
commit: ea0453ee979174d6fc14aae0fd85e4ede6742a86
branch: main
author: Diego Russo <diego.ru...@arm.com>
committer: brandtbucher <brandtbuc...@gmail.com>
date: 2025-03-25T10:15:36-07:00
summary:
GH-130887: Always remove trailing jumps in AArch64 JIT stencils (GH-131042)
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2025-03-10-12-08-57.gh-issue-130887.f823Ih.rst
M Tools/jit/_stencils.py
M Tools/jit/_targets.py
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2025-03-10-12-08-57.gh-issue-130887.f823Ih.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2025-03-10-12-08-57.gh-issue-130887.f823Ih.rst
new file mode 100644
index 00000000000000..daf9c8ea09f081
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2025-03-10-12-08-57.gh-issue-130887.f823Ih.rst
@@ -0,0 +1 @@
+Optimize the AArch64 code generation for the JIT. Patch by Diego Russo
diff --git a/Tools/jit/_stencils.py b/Tools/jit/_stencils.py
index 4ddbe967438bd1..8faa9e8cac2d85 100644
--- a/Tools/jit/_stencils.py
+++ b/Tools/jit/_stencils.py
@@ -209,7 +209,24 @@ def pad(self, alignment: int) -> None:
self.disassembly.append(f"{offset:x}: {' '.join(['00'] *
padding)}")
self.body.extend([0] * padding)
- def remove_jump(self, *, alignment: int = 1) -> None:
+ def add_nops(self, nop: bytes, alignment: int) -> None:
+ """Add NOPs until there is alignment. Fail if it is not possible."""
+ offset = len(self.body)
+ nop_size = len(nop)
+
+ # Calculate the gap to the next multiple of alignment.
+ gap = -offset % alignment
+ if gap:
+ if gap % nop_size == 0:
+ count = gap // nop_size
+ self.body.extend(nop * count)
+ else:
+ raise ValueError(
+ f"Cannot add nops of size '{nop_size}' to a body with "
+ f"offset '{offset}' to align with '{alignment}'"
+ )
+
+ def remove_jump(self) -> None:
"""Remove a zero-length continuation jump, if it exists."""
hole = max(self.holes, key=lambda hole: hole.offset)
match hole:
@@ -244,7 +261,7 @@ def remove_jump(self, *, alignment: int = 1) -> None:
jump = b"\x00\x00\x00\x14"
case _:
return
- if self.body[offset:] == jump and offset % alignment == 0:
+ if self.body[offset:] == jump:
self.body = self.body[:offset]
self.holes.remove(hole)
@@ -266,10 +283,7 @@ class StencilGroup:
_trampolines: set[int] = dataclasses.field(default_factory=set, init=False)
def process_relocations(
- self,
- known_symbols: dict[str, int],
- *,
- alignment: int = 1,
+ self, known_symbols: dict[str, int], *, alignment: int = 1, nop: bytes
= b""
) -> None:
"""Fix up all GOT and internal relocations for this stencil group."""
for hole in self.code.holes.copy():
@@ -289,8 +303,8 @@ def process_relocations(
self._trampolines.add(ordinal)
hole.addend = ordinal
hole.symbol = None
- self.code.remove_jump(alignment=alignment)
- self.code.pad(alignment)
+ self.code.remove_jump()
+ self.code.add_nops(nop=nop, alignment=alignment)
self.data.pad(8)
for stencil in [self.code, self.data]:
for hole in stencil.holes:
diff --git a/Tools/jit/_targets.py b/Tools/jit/_targets.py
index aa2b56abf446b1..b5a839e07d4daf 100644
--- a/Tools/jit/_targets.py
+++ b/Tools/jit/_targets.py
@@ -44,6 +44,15 @@ class _Target(typing.Generic[_S, _R]):
verbose: bool = False
known_symbols: dict[str, int] = dataclasses.field(default_factory=dict)
+ def _get_nop(self) -> bytes:
+ if re.fullmatch(r"aarch64-.*", self.triple):
+ nop = b"\x1f\x20\x03\xD5"
+ elif re.fullmatch(r"x86_64-.*|i686.*", self.triple):
+ nop = b"\x90"
+ else:
+ raise ValueError(f"NOP not defined for {self.triple}")
+ return nop
+
def _compute_digest(self, out: pathlib.Path) -> str:
hasher = hashlib.sha256()
hasher.update(self.triple.encode())
@@ -172,7 +181,9 @@ async def _build_stencils(self) -> dict[str,
_stencils.StencilGroup]:
stencil_groups = {task.get_name(): task.result() for task in tasks}
for stencil_group in stencil_groups.values():
stencil_group.process_relocations(
- known_symbols=self.known_symbols, alignment=self.alignment
+ known_symbols=self.known_symbols,
+ alignment=self.alignment,
+ nop=self._get_nop(),
)
return stencil_groups
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