gh-104584: Move super-instruction special-casing to generator (#106500)

Instead of special-casing specific instructions,
we add a few more special values to the 'size' field of expansions,
so in the future we can automatically handle
additional super-instructions in the generator.

Tools/cases_generator/generate_cases.py

@@ -40,6 +40,17 @@ RE_PREDICTED = (
 UNUSED = "unused"
 BITS_PER_CODE_UNIT = 16
 
+# Constants used instead of size for macro expansions.
+# Note: 1, 2, 4 must match actual cache entry sizes.
+OPARG_SIZES = {
+    "OPARG_FULL": 0,
+    "OPARG_CACHE_1": 1,
+    "OPARG_CACHE_2": 2,
+    "OPARG_CACHE_4": 4,
+    "OPARG_TOP": 5,
+    "OPARG_BOTTOM": 6,
+}
+
 RESERVED_WORDS = {
     "co_consts" : "Use FRAME_CO_CONSTS.",
     "co_names": "Use FRAME_CO_NAMES.",
@@ -1213,7 +1224,10 @@ class Analyzer:
                 self.out.emit("struct { int16_t uop; int8_t size; int8_t offset; } uops[8];")
             self.out.emit("")
 
+            for key, value in OPARG_SIZES.items():
+                self.out.emit(f"#define {key} {value}")
             self.out.emit("")
+
             self.out.emit("#define OPCODE_METADATA_FMT(OP) "
                           "(_PyOpcode_opcode_metadata[(OP)].instr_format)")
             self.out.emit("#define SAME_OPCODE_METADATA(OP1, OP2) \\")
@@ -1263,6 +1277,9 @@ class Analyzer:
                                 # Construct a dummy Component -- input/output mappings are not used
                                 part = Component(instr, [], [], instr.active_caches)
                                 self.write_macro_expansions(instr.name, [part])
+                            elif instr.kind == "inst" and variable_used(instr.inst, "oparg1"):
+                                assert variable_used(instr.inst, "oparg2"), "Half super-instr?"
+                                self.write_super_expansions(instr.name)
                         case parser.Macro():
                             mac = self.macro_instrs[thing.name]
                             self.write_macro_expansions(mac.name, mac.parts)
@@ -1342,7 +1359,7 @@ class Analyzer:
                     print(f"NOTE: Part {part.instr.name} of {name} is not a viable uop")
                     return
                 if part.instr.instr_flags.HAS_ARG_FLAG or not part.active_caches:
-                    size, offset = 0, 0
+                    size, offset = OPARG_SIZES["OPARG_FULL"], 0
                 else:
                     # If this assert triggers, is_viable_uops() lied
                     assert len(part.active_caches) == 1, (name, part.instr.name)
@@ -1350,10 +1367,50 @@ class Analyzer:
                     size, offset = cache.effect.size, cache.offset
                 expansions.append((part.instr.name, size, offset))
         assert len(expansions) > 0, f"Macro {name} has empty expansion?!"
+        self.write_expansions(name, expansions)
+
+    def write_super_expansions(self, name: str) -> None:
+        """Write special macro expansions for super-instructions.
+
+        If you get an assertion failure here, you probably have accidentally
+        violated one of the assumptions here.
+
+        - A super-instruction's name is of the form FIRST_SECOND where
+          FIRST and SECOND are regular instructions whose name has the
+          form FOO_BAR. Thus, there must be exactly 3 underscores.
+          Example: LOAD_CONST_STORE_FAST.
+
+        - A super-instruction's body uses `oparg1 and `oparg2`, and no
+          other instruction's body uses those variable names.
+
+        - A super-instruction has no active (used) cache entries.
+
+        In the expansion, the first instruction's operand is all but the
+        bottom 4 bits of the super-instruction's oparg, and the second
+        instruction's operand is the bottom 4 bits. We use the special
+        size codes OPARG_TOP and OPARG_BOTTOM for these.
+        """
+        pieces = name.split("_")
+        assert len(pieces) == 4, f"{name} doesn't look like a super-instr"
+        name1 = "_".join(pieces[:2])
+        name2 = "_".join(pieces[2:])
+        assert name1 in self.instrs, f"{name1} doesn't match any instr"
+        assert name2 in self.instrs, f"{name2} doesn't match any instr"
+        instr1 = self.instrs[name1]
+        instr2 = self.instrs[name2]
+        assert not instr1.active_caches, f"{name1} has active caches"
+        assert not instr2.active_caches, f"{name2} has active caches"
+        expansions = [
+            (name1, OPARG_SIZES["OPARG_TOP"], 0),
+            (name2, OPARG_SIZES["OPARG_BOTTOM"], 0),
+        ]
+        self.write_expansions(name, expansions)
+
+    def write_expansions(self, name: str, expansions: list[tuple[str, int, int]]) -> None:
         pieces = [f"{{ {name}, {size}, {offset} }}" for name, size, offset in expansions]
         self.out.emit(
             f"[{name}] = "
-            f"{{ .nuops = {len(expansions)}, .uops = {{ {', '.join(pieces)} }} }},"
+            f"{{ .nuops = {len(pieces)}, .uops = {{ {', '.join(pieces)} }} }},"
         )
 
     def emit_metadata_entry(