diff --git a/tests/unit/compiler/venom/test_multi_entry_block.py b/tests/unit/compiler/venom/test_multi_entry_block.py
index cc148416a5..47f4b88707 100644
--- a/tests/unit/compiler/venom/test_multi_entry_block.py
+++ b/tests/unit/compiler/venom/test_multi_entry_block.py
@@ -39,7 +39,7 @@ def test_multi_entry_block_1():
     assert ctx.normalized, "CFG should be normalized"
 
     finish_bb = ctx.get_basic_block(finish_label.value)
-    cfg_in = list(finish_bb.cfg_in.keys())
+    cfg_in = list(finish_bb.cfg_in)
     assert cfg_in[0].label.value == "target", "Should contain target"
     assert cfg_in[1].label.value == "__global_split_finish", "Should contain __global_split_finish"
     assert cfg_in[2].label.value == "block_1_split_finish", "Should contain block_1_split_finish"
@@ -91,7 +91,7 @@ def test_multi_entry_block_2():
     assert ctx.normalized, "CFG should be normalized"
 
     finish_bb = ctx.get_basic_block(finish_label.value)
-    cfg_in = list(finish_bb.cfg_in.keys())
+    cfg_in = list(finish_bb.cfg_in)
     assert cfg_in[0].label.value == "target", "Should contain target"
     assert cfg_in[1].label.value == "__global_split_finish", "Should contain __global_split_finish"
     assert cfg_in[2].label.value == "block_1_split_finish", "Should contain block_1_split_finish"
@@ -132,7 +132,7 @@ def test_multi_entry_block_with_dynamic_jump():
     assert ctx.normalized, "CFG should be normalized"
 
     finish_bb = ctx.get_basic_block(finish_label.value)
-    cfg_in = list(finish_bb.cfg_in.keys())
+    cfg_in = list(finish_bb.cfg_in)
     assert cfg_in[0].label.value == "target", "Should contain target"
     assert cfg_in[1].label.value == "__global_split_finish", "Should contain __global_split_finish"
     assert cfg_in[2].label.value == "block_1_split_finish", "Should contain block_1_split_finish"
diff --git a/vyper/utils.py b/vyper/utils.py
index ba615e58d7..0fd74b8972 100644
--- a/vyper/utils.py
+++ b/vyper/utils.py
@@ -1,4 +1,5 @@
 import binascii
+import itertools
 import contextlib
 import decimal
 import enum
@@ -15,7 +16,7 @@
 _T = TypeVar("_T")
 
 
-class OrderedSet(Generic[_T], dict[_T, None]):
+class OrderedSet(Generic[_T]):
     """
     a minimal "ordered set" class. this is needed in some places
     because, while dict guarantees you can recover insertion order
@@ -25,57 +26,82 @@ class OrderedSet(Generic[_T], dict[_T, None]):
     """
 
     def __init__(self, iterable=None):
-        super().__init__()
+        self._data = dict()
         if iterable is not None:
-            for item in iterable:
-                self.add(item)
+            self.update(iterable)
 
     def __repr__(self):
-        keys = ", ".join(repr(k) for k in self.keys())
+        keys = ", ".join(repr(k) for k in self)
         return f"{{{keys}}}"
 
-    def get(self, *args, **kwargs):
-        raise RuntimeError("can't call get() on OrderedSet!")
+    def __iter__(self):
+        return iter(self._data)
+
+    def __contains__(self, item):
+        return self._data.__contains__(item)
+
+    def __len__(self):
+        return len(self._data)
 
     def first(self):
         return next(iter(self))
 
     def add(self, item: _T) -> None:
-        self[item] = None
+        self._data[item] = None
 
     def remove(self, item: _T) -> None:
-        del self[item]
+        del self._data[item]
+
+    def drop(self, item: _T):
+        # friendly version of remove
+        self._data.pop(item, None)
+
+    def dropmany(self, iterable):
+        for item in iterable:
+            self._data.pop(item, None)
 
     def difference(self, other):
         ret = self.copy()
-        for k in other.keys():
-            if k in ret:
-                ret.remove(k)
+        ret.dropmany(other)
         return ret
 
+    def update(self, other):
+        # CMC 2024-03-22 for some reason, this is faster than dict.update?
+        # (maybe size dependent)
+        for item in other:
+            self._data[item] = None
+
     def union(self, other):
         return self | other
 
-    def update(self, other):
-        super().update(self.__class__.fromkeys(other))
+    def __ior__(self, other):
+        self.update(other)
+        return self
 
     def __or__(self, other):
-        return self.__class__(super().__or__(other))
+        ret = self.copy()
+        ret.update(other)
+        return ret
+
+    def __eq__(self, other):
+        return self._data == other._data
 
     def copy(self):
-        return self.__class__(super().copy())
+        cls = self.__class__
+        ret = cls.__new__(cls)
+        ret._data = self._data.copy()
+        return ret
 
     @classmethod
     def intersection(cls, *sets):
-        res = OrderedSet()
         if len(sets) == 0:
             raise ValueError("undefined: intersection of no sets")
-        if len(sets) == 1:
-            return sets[0].copy()
-        for e in sets[0].keys():
-            if all(e in s for s in sets[1:]):
-                res.add(e)
-        return res
+
+        ret = sets[0].copy()
+        for e in sets[0]:
+            if any(e not in s for s in sets[1:]):
+                ret.remove(e)
+        return ret
 
 
 class StringEnum(enum.Enum):
diff --git a/vyper/venom/analysis.py b/vyper/venom/analysis.py
index 0bc1ec0fac..4be4e48f28 100644
--- a/vyper/venom/analysis.py
+++ b/vyper/venom/analysis.py
@@ -1,4 +1,5 @@
 from typing import Optional
+import itertools
 
 from vyper.exceptions import CompilerPanic
 from vyper.utils import OrderedSet
@@ -53,12 +54,15 @@ def _calculate_liveness(bb: IRBasicBlock) -> bool:
     orig_liveness = bb.instructions[0].liveness.copy()
     liveness = bb.out_vars.copy()
     for instruction in reversed(bb.instructions):
-        ops = instruction.get_inputs()
+        ins = instruction.get_inputs()
+        outs = instruction.get_outputs()
+
+        if ins or outs:
+            # perf: only copy if changed
+            liveness = liveness.copy()
+            liveness.update(ins)
+            liveness.dropmany(outs)
 
-        liveness = liveness.union(OrderedSet.fromkeys(ops))
-        out = instruction.get_outputs()[0] if len(instruction.get_outputs()) > 0 else None
-        if out in liveness:
-            liveness.remove(out)
         instruction.liveness = liveness
 
     return orig_liveness != bb.instructions[0].liveness
diff --git a/vyper/venom/basicblock.py b/vyper/venom/basicblock.py
index 3171fd0172..2bfeaea2a9 100644
--- a/vyper/venom/basicblock.py
+++ b/vyper/venom/basicblock.py
@@ -1,5 +1,6 @@
 from enum import Enum, auto
 from typing import TYPE_CHECKING, Any, Generator, Iterator, Optional, Union
+from functools import cached_property
 
 from vyper.utils import OrderedSet
 
diff --git a/vyper/venom/dominators.py b/vyper/venom/dominators.py
index ce6a4868cf..d11d61cec3 100644
--- a/vyper/venom/dominators.py
+++ b/vyper/venom/dominators.py
@@ -58,7 +58,7 @@ def _compute_dominators(self):
         """
         basic_blocks = list(self.dfs_order.keys())
         self.dominators = {bb: OrderedSet(basic_blocks) for bb in basic_blocks}
-        self.dominators[self.entry_block] = OrderedSet({self.entry_block})
+        self.dominators[self.entry_block] = OrderedSet([self.entry_block])
         changed = True
         count = len(basic_blocks) ** 2  # TODO: find a proper bound for this
         while changed:
diff --git a/vyper/venom/function.py b/vyper/venom/function.py
index 81d46fec3e..e52343ca32 100644
--- a/vyper/venom/function.py
+++ b/vyper/venom/function.py
@@ -49,6 +49,7 @@ def __init__(self, name: IRLabel = None) -> None:
 
         self._ast_source_stack = []
         self._error_msg_stack = []
+        self._bb_index = {}
 
         self.add_entry_point(name)
         self.append_basic_block(IRBasicBlock(name, self))
@@ -76,6 +77,15 @@ def append_basic_block(self, bb: IRBasicBlock) -> IRBasicBlock:
 
         return self.basic_blocks[-1]
 
+    def _get_basicblock_index(self, label: str):
+        ix = self._bb_index.get(label, -1)
+        if 0 <= ix < len(self.basic_blocks) and self.basic_blocks[ix].label == label:
+            return ix
+        # do a reindex
+        self._bb_index = dict((bb.label, ix) for ix, bb in enumerate(self.basic_blocks))
+        return self._bb_index[label]
+
+
     def get_basic_block(self, label: Optional[str] = None) -> IRBasicBlock:
         """
         Get basic block by label.
@@ -83,18 +93,16 @@ def get_basic_block(self, label: Optional[str] = None) -> IRBasicBlock:
         """
         if label is None:
             return self.basic_blocks[-1]
-        for bb in self.basic_blocks:
-            if bb.label.value == label:
-                return bb
-        raise AssertionError(f"Basic block '{label}' not found")
+        ix = self._get_basicblock_index(label)
+        return self.basic_blocks[ix]
 
     def get_basic_block_after(self, label: IRLabel) -> IRBasicBlock:
         """
         Get basic block after label.
         """
-        for i, bb in enumerate(self.basic_blocks[:-1]):
-            if bb.label.value == label.value:
-                return self.basic_blocks[i + 1]
+        ix = self._get_basicblock_index(label.value)
+        if 0 <= ix < len(self.basic_blocks) - 1:
+            return self.basic_blocks[ix + 1]
         raise AssertionError(f"Basic block after '{label}' not found")
 
     def get_terminal_basicblocks(self) -> Iterator[IRBasicBlock]:
diff --git a/vyper/venom/venom_to_assembly.py b/vyper/venom/venom_to_assembly.py
index d702b8dc2b..0cb13becf2 100644
--- a/vyper/venom/venom_to_assembly.py
+++ b/vyper/venom/venom_to_assembly.py
@@ -407,7 +407,7 @@ def _generate_evm_for_instruction(
             # NOTE: stack in general can contain multiple copies of the same variable,
             # however we are safe in the case of jmp/djmp/jnz as it's not going to
             # have multiples.
-            target_stack_list = list(target_stack.keys())
+            target_stack_list = list(target_stack)
             self._stack_reorder(assembly, stack, target_stack_list)
 
         # final step to get the inputs to this instruction ordered