GH-113464: Add a JIT backend for tier 2 (GH-113465)

Add an option (--enable-experimental-jit for configure-based builds
or --experimental-jit for PCbuild-based ones) to build an
*experimental* just-in-time compiler, based on copy-and-patch (https://fredrikbk.com/publications/copy-and-patch.pdf).

See Tools/jit/README.md for more information on how to install the required build-time tooling.

Tools/jit/_writer.py

@@ -0,0 +1,95 @@
+"""Utilities for writing StencilGroups out to a C header file."""
+import typing
+
+import _schema
+import _stencils
+
+
+def _dump_header() -> typing.Iterator[str]:
+    yield "typedef enum {"
+    for kind in typing.get_args(_schema.HoleKind):
+        yield f"    HoleKind_{kind},"
+    yield "} HoleKind;"
+    yield ""
+    yield "typedef enum {"
+    for value in _stencils.HoleValue:
+        yield f"    HoleValue_{value.name},"
+    yield "} HoleValue;"
+    yield ""
+    yield "typedef struct {"
+    yield "    const uint64_t offset;"
+    yield "    const HoleKind kind;"
+    yield "    const HoleValue value;"
+    yield "    const void *symbol;"
+    yield "    const uint64_t addend;"
+    yield "} Hole;"
+    yield ""
+    yield "typedef struct {"
+    yield "    const size_t body_size;"
+    yield "    const unsigned char * const body;"
+    yield "    const size_t holes_size;"
+    yield "    const Hole * const holes;"
+    yield "} Stencil;"
+    yield ""
+    yield "typedef struct {"
+    yield "    const Stencil code;"
+    yield "    const Stencil data;"
+    yield "} StencilGroup;"
+    yield ""
+
+
+def _dump_footer(opnames: typing.Iterable[str]) -> typing.Iterator[str]:
+    yield "#define INIT_STENCIL(STENCIL) {                         \\"
+    yield "    .body_size = Py_ARRAY_LENGTH(STENCIL##_body) - 1,   \\"
+    yield "    .body = STENCIL##_body,                             \\"
+    yield "    .holes_size = Py_ARRAY_LENGTH(STENCIL##_holes) - 1, \\"
+    yield "    .holes = STENCIL##_holes,                           \\"
+    yield "}"
+    yield ""
+    yield "#define INIT_STENCIL_GROUP(OP) {     \\"
+    yield "    .code = INIT_STENCIL(OP##_code), \\"
+    yield "    .data = INIT_STENCIL(OP##_data), \\"
+    yield "}"
+    yield ""
+    yield "static const StencilGroup stencil_groups[512] = {"
+    for opname in opnames:
+        yield f"    [{opname}] = INIT_STENCIL_GROUP({opname}),"
+    yield "};"
+    yield ""
+    yield "#define GET_PATCHES() { \\"
+    for value in _stencils.HoleValue:
+        yield f"    [HoleValue_{value.name}] = (uint64_t)0xBADBADBADBADBADB, \\"
+    yield "}"
+
+
+def _dump_stencil(opname: str, group: _stencils.StencilGroup) -> typing.Iterator[str]:
+    yield f"// {opname}"
+    for part, stencil in [("code", group.code), ("data", group.data)]:
+        for line in stencil.disassembly:
+            yield f"// {line}"
+        if stencil.body:
+            size = len(stencil.body) + 1
+            yield f"static const unsigned char {opname}_{part}_body[{size}] = {{"
+            for i in range(0, len(stencil.body), 8):
+                row = " ".join(f"{byte:#04x}," for byte in stencil.body[i : i + 8])
+                yield f"    {row}"
+            yield "};"
+        else:
+            yield f"static const unsigned char {opname}_{part}_body[1];"
+        if stencil.holes:
+            size = len(stencil.holes) + 1
+            yield f"static const Hole {opname}_{part}_holes[{size}] = {{"
+            for hole in stencil.holes:
+                yield f"    {hole.as_c()},"
+            yield "};"
+        else:
+            yield f"static const Hole {opname}_{part}_holes[1];"
+    yield ""
+
+
+def dump(groups: dict[str, _stencils.StencilGroup]) -> typing.Iterator[str]:
+    """Yield a JIT compiler line-by-line as a C header file."""
+    yield from _dump_header()
+    for opname, group in groups.items():
+        yield from _dump_stencil(opname, group)
+    yield from _dump_footer(groups)