GH-111485: Generate `TARGET` table for computed goto dispatch. (GH-113319)

Makefile.pre.in

@@ -1587,11 +1587,12 @@ regen-cases:
 	$(PYTHON_FOR_REGEN) \
 	    $(srcdir)/Tools/cases_generator/generate_cases.py \
 		$(CASESFLAG) \
-		-t $(srcdir)/Python/opcode_targets.h.new \
 		-a $(srcdir)/Python/abstract_interp_cases.c.h.new \
 		$(srcdir)/Python/bytecodes.c
 	$(PYTHON_FOR_REGEN) $(srcdir)/Tools/cases_generator/opcode_id_generator.py \
 	    -o $(srcdir)/Include/opcode_ids.h.new $(srcdir)/Python/bytecodes.c
+	$(PYTHON_FOR_REGEN) $(srcdir)/Tools/cases_generator/target_generator.py \
+	    -o $(srcdir)/Python/opcode_targets.h.new $(srcdir)/Python/bytecodes.c
 	$(PYTHON_FOR_REGEN) $(srcdir)/Tools/cases_generator/uop_id_generator.py \
 	    -o $(srcdir)/Include/internal/pycore_uop_ids.h.new $(srcdir)/Python/bytecodes.c
 	$(PYTHON_FOR_REGEN) $(srcdir)/Tools/cases_generator/py_metadata_generator.py \

Python/opcode_targets.h

@@ -254,4 +254,5 @@ static void *opcode_targets[256] = {
     &&TARGET_INSTRUMENTED_POP_JUMP_IF_NONE,
     &&TARGET_INSTRUMENTED_POP_JUMP_IF_NOT_NONE,
     &&TARGET_INSTRUMENTED_LINE,
-    &&_unknown_opcode};
+    &&_unknown_opcode,
+};

Tools/cases_generator/generate_cases.py

@@ -839,7 +839,6 @@ def main() -> None:
     # These raise OSError if output can't be written
 
     a.assign_opcode_ids()
-    a.write_opcode_targets(args.opcode_targets_h)
     a.write_abstract_interpreter_instructions(
         args.abstract_interpreter_cases, args.emit_line_directives
     )

Tools/cases_generator/target_generator.py

@@ -0,0 +1,54 @@
+"""Generate targets for computed goto dispatch
+Reads the instruction definitions from bytecodes.c.
+Writes the table to opcode_targets.h by default.
+"""
+
+import argparse
+
+from analyzer import (
+    Analysis,
+    analyze_files,
+)
+from generators_common import (
+    DEFAULT_INPUT,
+    ROOT,
+)
+from cwriter import CWriter
+from typing import TextIO
+
+
+DEFAULT_OUTPUT = ROOT / "Python/opcode_targets.h"
+
+
+def write_opcode_targets(analysis: Analysis, out: CWriter) -> None:
+    """Write header file that defines the jump target table"""
+    targets = ["&&_unknown_opcode,\n"] * 256
+    for name, op in analysis.opmap.items():
+        if op < 256:
+            targets[op] = f"&&TARGET_{name},\n"
+    out.emit("static void *opcode_targets[256] = {\n")
+    for target in targets:
+        out.emit(target)
+    out.emit("};\n")
+
+arg_parser = argparse.ArgumentParser(
+    description="Generate the file with dispatch targets.",
+    formatter_class=argparse.ArgumentDefaultsHelpFormatter,
+)
+
+arg_parser.add_argument(
+    "-o", "--output", type=str, help="Generated code", default=DEFAULT_OUTPUT
+)
+
+arg_parser.add_argument(
+    "input", nargs=argparse.REMAINDER, help="Instruction definition file(s)"
+)
+
+if __name__ == "__main__":
+    args = arg_parser.parse_args()
+    if len(args.input) == 0:
+        args.input.append(DEFAULT_INPUT)
+    data = analyze_files(args.input)
+    with open(args.output, "w") as outfile:
+        out = CWriter(outfile, 0, False)
+        write_opcode_targets(data, out)