GH-98831: Implement super-instruction generation (#99084)

Co-authored-by: C.A.M. Gerlach <[email protected]>

Author: gvanrossum

Misc/NEWS.d/next/Build/2022-10-28-22-24-26.gh-issue-98831.IXRCRX.rst

@@ -1 +1,9 @@
-We have new tooling, in ``Tools/cases_generator``, to generate the interpreter switch from a list of opcode definitions.
+Add new tooling, in ``Tools/cases_generator``,
+to generate the interpreter switch statement from a list of opcode definitions.
+This only affects adding, modifying or removing instruction definitions.
+The instruction definitions now live in ``Python/bytecodes.c``,
+in the form of a `custom DSL (under development)
+<https://github.com/faster-cpython/ideas/blob/main/3.12/interpreter_definition.md>`__.
+The tooling reads this file and writes ``Python/generated_cases.c.h``,
+which is then included by ``Python/ceval.c`` to provide most of the cases
+of the main interpreter switch.

Python/bytecodes.c

@@ -69,6 +69,7 @@ do { \
 #define DISPATCH() ((void)0)
 
 #define inst(name) case name:
+#define super(name) static int SUPER_##name
 #define family(name) static int family_##name
 
 #define NAME_ERROR_MSG \
@@ -158,67 +159,11 @@ dummy_func(
             SETLOCAL(oparg, value);
         }
 
-        // stack effect: ( -- __0, __1)
-        inst(LOAD_FAST__LOAD_FAST) {
-            PyObject *value = GETLOCAL(oparg);
-            assert(value != NULL);
-            NEXTOPARG();
-            next_instr++;
-            Py_INCREF(value);
-            PUSH(value);
-            value = GETLOCAL(oparg);
-            assert(value != NULL);
-            Py_INCREF(value);
-            PUSH(value);
-        }
-
-        // stack effect: ( -- __0, __1)
-        inst(LOAD_FAST__LOAD_CONST) {
-            PyObject *value = GETLOCAL(oparg);
-            assert(value != NULL);
-            NEXTOPARG();
-            next_instr++;
-            Py_INCREF(value);
-            PUSH(value);
-            value = GETITEM(consts, oparg);
-            Py_INCREF(value);
-            PUSH(value);
-        }
-
-        // stack effect: ( -- )
-        inst(STORE_FAST__LOAD_FAST) {
-            PyObject *value = POP();
-            SETLOCAL(oparg, value);
-            NEXTOPARG();
-            next_instr++;
-            value = GETLOCAL(oparg);
-            assert(value != NULL);
-            Py_INCREF(value);
-            PUSH(value);
-        }
-
-        // stack effect: (__0, __1 -- )
-        inst(STORE_FAST__STORE_FAST) {
-            PyObject *value = POP();
-            SETLOCAL(oparg, value);
-            NEXTOPARG();
-            next_instr++;
-            value = POP();
-            SETLOCAL(oparg, value);
-        }
-
-        // stack effect: ( -- __0, __1)
-        inst(LOAD_CONST__LOAD_FAST) {
-            PyObject *value = GETITEM(consts, oparg);
-            NEXTOPARG();
-            next_instr++;
-            Py_INCREF(value);
-            PUSH(value);
-            value = GETLOCAL(oparg);
-            assert(value != NULL);
-            Py_INCREF(value);
-            PUSH(value);
-        }
+        super(LOAD_FAST__LOAD_FAST) = LOAD_FAST + LOAD_FAST;
+        super(LOAD_FAST__LOAD_CONST) = LOAD_FAST + LOAD_CONST;
+        super(STORE_FAST__LOAD_FAST)  = STORE_FAST + LOAD_FAST;
+        super(STORE_FAST__STORE_FAST) = STORE_FAST + STORE_FAST;
+        super (LOAD_CONST__LOAD_FAST) = LOAD_CONST + LOAD_FAST;
 
         // stack effect: (__0 -- )
         inst(POP_TOP) {

Python/generated_cases.c.h

@@ -11,7 +11,7 @@
 import sys
 
 import parser
-from parser import InstDef
+from parser import InstDef  # TODO: Use parser.InstDef
 
 arg_parser = argparse.ArgumentParser()
 arg_parser.add_argument("-i", "--input", type=str, default="Python/bytecodes.c")
@@ -29,19 +29,24 @@ def eopen(filename: str, mode: str = "r"):
     return open(filename, mode)
 
 
-def parse_cases(src: str, filename: str|None = None) -> tuple[list[InstDef], list[parser.Family]]:
+def parse_cases(
+    src: str, filename: str|None = None
+) -> tuple[list[InstDef], list[parser.Super], list[parser.Family]]:
     psr = parser.Parser(src, filename=filename)
     instrs: list[InstDef] = []
+    supers: list[parser.Super] = []
     families: list[parser.Family] = []
     while not psr.eof():
         if inst := psr.inst_def():
             assert inst.block
-            instrs.append(InstDef(inst.name, inst.inputs, inst.outputs, inst.block))
+            instrs.append(inst)
+        elif sup := psr.super_def():
+            supers.append(sup)
         elif fam := psr.family_def():
             families.append(fam)
         else:
             raise psr.make_syntax_error(f"Unexpected token")
-    return instrs, families
+    return instrs, supers, families
 
 
 def always_exits(block: parser.Block) -> bool:
@@ -62,16 +67,18 @@ def always_exits(block: parser.Block) -> bool:
     return line.startswith(("goto ", "return ", "DISPATCH", "GO_TO_", "Py_UNREACHABLE()"))
 
 
-def write_cases(f: io.TextIOBase, instrs: list[InstDef]):
+def write_cases(f: io.TextIOBase, instrs: list[InstDef], supers: list[parser.Super]):
     predictions = set()
     for inst in instrs:
         for target in re.findall(r"(?:PREDICT|GO_TO_INSTRUCTION)\((\w+)\)", inst.block.text):
             predictions.add(target)
     indent = "        "
     f.write(f"// This file is generated by {os.path.relpath(__file__)}\n")
     f.write("// Do not edit!\n")
+    instr_index: dict[str, InstDef] = {}
     for instr in instrs:
         assert isinstance(instr, InstDef)
+        instr_index[instr.name] = instr
         f.write(f"\n{indent}TARGET({instr.name}) {{\n")
         if instr.name in predictions:
             f.write(f"{indent}    PREDICTED({instr.name});\n")
@@ -102,6 +109,22 @@ def write_cases(f: io.TextIOBase, instrs: list[InstDef]):
         # Write trailing '}'
         f.write(f"{indent}}}\n")
 
+    for sup in supers:
+        assert isinstance(sup, parser.Super)
+        components = [instr_index[name] for name in sup.ops]
+        f.write(f"\n{indent}TARGET({sup.name}) {{\n")
+        for i, instr in enumerate(components):
+            if i > 0:
+                f.write(f"{indent}    NEXTOPARG();\n")
+                f.write(f"{indent}    next_instr++;\n")
+            text = instr.block.to_text(-4)
+            textlines = text.splitlines(True)
+            textlines = [line for line in textlines if not line.strip().startswith("PREDICTED(")]
+            text = "".join(textlines)
+            f.write(f"{indent}    {text.strip()}\n")
+        f.write(f"{indent}    DISPATCH();\n")
+        f.write(f"{indent}}}\n")
+
 
 def main():
     args = arg_parser.parse_args()
@@ -110,21 +133,22 @@ def main():
     begin = srclines.index("// BEGIN BYTECODES //")
     end = srclines.index("// END BYTECODES //")
     src = "\n".join(srclines[begin+1 : end])
-    instrs, families = parse_cases(src, filename=args.input)
-    ninstrs = nfamilies = 0
+    instrs, supers, families = parse_cases(src, filename=args.input)
+    ninstrs = nsupers = nfamilies = 0
     if not args.quiet:
         ninstrs = len(instrs)
+        nsupers = len(supers)
         nfamilies = len(families)
         print(
-            f"Read {ninstrs} instructions "
+            f"Read {ninstrs} instructions, {nsupers} supers, "
             f"and {nfamilies} families from {args.input}",
             file=sys.stderr,
         )
     with eopen(args.output, "w") as f:
-        write_cases(f, instrs)
+        write_cases(f, instrs, supers)
     if not args.quiet:
         print(
-            f"Wrote {ninstrs} instructions to {args.output}",
+            f"Wrote {ninstrs + nsupers} instructions to {args.output}",
             file=sys.stderr,
         )