diff --git a/Lib/test/test_generated_cases.py b/Lib/test/test_generated_cases.py
index 98bc8ecc3f7ce6..d0e988c3e8fb87 100644
--- a/Lib/test/test_generated_cases.py
+++ b/Lib/test/test_generated_cases.py
@@ -2,8 +2,10 @@
 import os
 import sys
 import tempfile
+import textwrap
 import unittest
 
+from io import StringIO
 from test import support
 from test import test_tools
 
@@ -30,9 +32,11 @@ def skip_if_different_mount_drives():
 test_tools.skip_if_missing("cases_generator")
 with test_tools.imports_under_tool("cases_generator"):
     from analyzer import analyze_forest, StackItem
+    from cwriter import CWriter
     import parser
     from stack import get_deeper_stack, get_stack_hwm, Local, Stack, StackError
     import tier1_generator
+    import opcode_metadata_generator
     import optimizer_generator
 
 
@@ -118,58 +122,28 @@ def test_XXX(self):
         print(s.top_offset.to_c())
 
 
-class TestGetHWM(unittest.TestCase):
-    def check(self, src, expected_vars):
-        analysis = analyze_forest(parse_src(src))
-        hwm = get_stack_hwm(analysis.instructions["OP"])
-        hwm_vars = [loc.item.name for loc in hwm.variables]
-        self.assertEqual(hwm_vars, expected_vars)
+class TestGenerateMaxStackEffect(unittest.TestCase):
+    def check(self, input, output):
+        analysis = analyze_forest(parse_src(input))
+        buf = StringIO()
+        writer = CWriter(buf, 0, False)
+        opcode_metadata_generator.generate_max_stack_effect_function(analysis, writer)
+        buf.seek(0)
+        self.assertIn(output.strip(), buf.read())
 
     def test_inst(self):
-        src = """
+        input = """
         inst(OP, (a -- b, c)) {
             SPAM();
         }
         """
-        self.check(src, ["b", "c"])
-
-    def test_uops(self):
-        src = """
-        op(OP0, (a -- b, c)) {
-            SPAM();
-        }
-
-        op(OP1, (b, c -- x)) {
-            SPAM();
-        }
-
-        op(OP2, (x -- x, y if (oparg))) {
-            SPAM();
-        }
-
-        macro(OP) = OP0 + OP1 + OP2;
-        """
-        self.check(src, ["b", "c"])
-
-    def test_incompatible_stacks(self):
-        src = """
-        op(OP0, (a -- b, c if (oparg & 1))) {
-            SPAM();
-        }
-
-        op(OP1, (b, c -- x)) {
-            SPAM();
-        }
-
-        op(OP2, (x -- x, y if (oparg & 2))) {
-            SPAM();
+        output = """
+        case OP: {
+            *effect = 1;
+            return 0;
         }
-
-        macro(OP) = OP0 + OP1 + OP2;
         """
-        with self.assertRaisesRegex(StackError,
-                                    "Cannot determine stack hwm for OP"):
-            self.check(src, [])
+        self.check(input, output)
 
 
 class TestGeneratedCases(unittest.TestCase):
diff --git a/Tools/cases_generator/opcode_metadata_generator.py b/Tools/cases_generator/opcode_metadata_generator.py
index 021e519d26e970..a658bd946603e0 100644
--- a/Tools/cases_generator/opcode_metadata_generator.py
+++ b/Tools/cases_generator/opcode_metadata_generator.py
@@ -19,8 +19,9 @@
     cflags,
 )
 from cwriter import CWriter
+from dataclasses import dataclass
 from typing import TextIO
-from stack import get_stack_effect, get_stack_hwm, get_deeper_stack
+from stack import Stack, get_stack_effect, get_stack_effects, get_stack_hwm, get_deeper_stack
 
 # Constants used instead of size for macro expansions.
 # Note: 1, 2, 4 must match actual cache entry sizes.
@@ -94,8 +95,6 @@ def generate_stack_effect_functions(analysis: Analysis, out: CWriter) -> None:
 
     def add(inst: Instruction | PseudoInstruction) -> None:
         stack = get_stack_effect(inst)
-        hwm = get_stack_hwm(inst)
-        print(f"{inst.name} - {hwm}")
         popped = (-stack.base_offset).to_c()
         pushed = (stack.top_offset - stack.base_offset).to_c()
         popped_data.append((inst.name, popped))
@@ -106,30 +105,101 @@ def add(inst: Instruction | PseudoInstruction) -> None:
     for pseudo in analysis.pseudos.values():
         add(pseudo)
 
-    def analyze_family(family):
-        hwm_inst = family.members[0]
-        hwm = get_stack_hwm(hwm_inst)
-        for inst in family.members[1:]:
-            inst_hwm = get_stack_hwm(inst)
-            deeper = get_deeper_stack(hwm, inst_hwm)
-            if deeper is None:
-                print(f"INCOMPATIBLE: {family.name}")
-                print(f"{inst.name} {inst_hwm.top_offset.to_c()}")
-                print(f"{hwm_inst.name} {hwm.top_offset.to_c()}")
-                return
-            elif deeper is not hwm:
-                hwm = deeper
-                hwm_inst = isnt
-        print(f"fam={name} hwm_inst={hwm_inst.name} hwm={hwm.top_offset.to_c()}")
-
-    for name, family in analysis.families.items():
-        analyze_family(family)
-
     emit_stack_effect_function(out, "popped", sorted(popped_data))
     emit_stack_effect_function(out, "pushed", sorted(pushed_data))
 
+    generate_max_stack_effect_function(analysis, out)
+
+
+def emit_max_stack_effect_function(
+    out: CWriter, effects: list[tuple[str, list[str]]]
+) -> None:
+    out.emit("extern int _PyOpcode_max_stack_effect(int opcode, int oparg, int *effect);\n")
+    out.emit("#ifdef NEED_OPCODE_METADATA\n")
+    out.emit(f"int _PyOpcode_max_stack_effect(int opcode, int oparg, int *effect)  {{\n")
+    out.emit("switch(opcode) {\n")
+    for name, exprs in effects:
+        out.emit(f"case {name}: {{\n")
+        if len(exprs) == 1:
+            out.emit(f"    *effect = {exprs[0]};\n")
+            out.emit(f"    return 0;\n")
+        else:
+            assert len(exprs) > 1
+            out.emit(f"    int max_eff = Py_MAX({exprs[0]}, {exprs[1]});\n")
+            for expr in exprs[2:]:
+                out.emit(f"    max_eff = Py_MAX(max_eff, {expr});\n")
+            out.emit(f"    *effect = max_eff;\n")
+            out.emit(f"    return 0;\n")
+        out.emit("}\n")
+    out.emit("default:\n")
+    out.emit("    return -1;\n")
+    out.emit("}\n")
+    out.emit("}\n\n")
+    out.emit("#endif\n\n")
+
+
+@dataclass
+class MaxStackEffectSet:
+    int_effect: int
+    cond_effects: set[str]
+
+    def __init__(self) -> None:
+        self.int_effect = 0
+        self.cond_effects = set()
+
+    def update(self, other: MaxStackEffectSet) -> None:
+        self.int_effect = max(self.int_effect, other.int_effect)
+        self.cond_effects.update(other.cond_effects)
+
+
+def generate_max_stack_effect_function(analysis: Analysis, out: CWriter) -> None:
+    """Generate a function that returns the maximum stack effect of an
+    instruction while it is executing.
+
+    Specialized instructions may have a greater stack effect during instruction
+    execution than the net stack effect of the instruction if uops pass
+    values on the stack.
+    """
+    effects: dict[str, MaxStackEffectSet] = {}
+
+    def add(inst: Instruction | PseudoInstruction) -> None:
+        inst_effect = MaxStackEffectSet()
+        for stack in get_stack_effects(inst):
+            popped = stack.base_offset
+            pushed = stack.top_offset - stack.base_offset
+            popped_int, pushed_int = popped.as_int(), pushed.as_int()
+            if popped_int is not None and pushed_int is not None:
+                int_effect = popped_int + pushed_int
+                if int_effect > inst_effect.int_effect:
+                    inst_effect.int_effect = int_effect
+            else:
+                inst_effect.cond_effects.add(f"({popped.to_c()}) + ({pushed.to_c()})")
+        effects[inst.name] = inst_effect
+
+    # Collect unique stack effects for each instruction
+    for inst in analysis.instructions.values():
+        add(inst)
+    for pseudo in analysis.pseudos.values():
+        add(pseudo)
+
+    # Merge the effects of all specializations in a family into the generic
+    # instruction
+    for family in analysis.families.values():
+        for inst in family.members:
+            effects[family.name].update(effects[inst.name])
+
+    data: list[tuple[str, list[str]]] = []
+    for name, effects in sorted(effects.items(), key=lambda kv: kv[0]):
+        exprs = []
+        if effects.int_effect is not None:
+            exprs.append(str(effects.int_effect))
+        exprs.extend(sorted(effects.cond_effects))
+        data.append((name, exprs))
+    emit_max_stack_effect_function(out, data)
+
 
 def generate_is_pseudo(analysis: Analysis, out: CWriter) -> None:
+
     """Write the IS_PSEUDO_INSTR macro"""
     out.emit("\n\n#define IS_PSEUDO_INSTR(OP)  ( \\\n")
     for op in analysis.pseudos:
diff --git a/Tools/cases_generator/stack.py b/Tools/cases_generator/stack.py
index ce3ad57706298e..bfabc98c3d65cd 100644
--- a/Tools/cases_generator/stack.py
+++ b/Tools/cases_generator/stack.py
@@ -390,18 +390,37 @@ def merge(self, other: "Stack", out: CWriter) -> None:
         self.align(other, out)
 
 
+def stacks(inst: Instruction | PseudoInstruction) -> Iterator[StackEffect]:
+    if isinstance(inst, Instruction):
+        for uop in inst.parts:
+            if isinstance(uop, Uop):
+                yield uop.stack
+    else:
+        assert isinstance(inst, PseudoInstruction)
+        yield inst.stack
+
+
 def get_stack_effect(inst: Instruction | PseudoInstruction) -> Stack:
     stack = Stack()
+    for s in stacks(inst):
+        locals: dict[str, Local] = {}
+        for var in reversed(s.inputs):
+            _, local = stack.pop(var)
+            if var.name != "unused":
+                locals[local.name] = local
+        for var in s.outputs:
+            if var.name in locals:
+                local = locals[var.name]
+            else:
+                local = Local.unused(var)
+            stack.push(local)
+    return stack
 
-    def stacks(inst: Instruction | PseudoInstruction) -> Iterator[StackEffect]:
-        if isinstance(inst, Instruction):
-            for uop in inst.parts:
-                if isinstance(uop, Uop):
-                    yield uop.stack
-        else:
-            assert isinstance(inst, PseudoInstruction)
-            yield inst.stack
 
+def get_stack_effects(inst: Instruction | PseudoInstruction) -> list[Stack]:
+    """Returns a list of stack effects after each uop"""
+    result = []
+    stack = Stack()
     for s in stacks(inst):
         locals: dict[str, Local] = {}
         for var in reversed(s.inputs):
@@ -414,7 +433,8 @@ def stacks(inst: Instruction | PseudoInstruction) -> Iterator[StackEffect]:
             else:
                 local = Local.unused(var)
             stack.push(local)
-    return stack
+        result.append(stack.copy())
+    return result
 
 
 @dataclass