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

2 files changed, 54 insertions, 1 deletions

diff --git a/Tools/cases_generator/generate_cases.py b/Tools/cases_generator/generate_cases.py
index bb027f3..73b5fc2 100644
--- a/Tools/cases_generator/generate_cases.py
+++ b/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
     )
diff --git a/Tools/cases_generator/target_generator.py b/Tools/cases_generator/target_generator.py
new file mode 100644
index 0000000..44a699c
--- /dev/null
+++ b/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)