diff --git a/mypyc/codegen/emitmodule.py b/mypyc/codegen/emitmodule.py
index 6c0dfd43b9af..0035bd53188b 100644
--- a/mypyc/codegen/emitmodule.py
+++ b/mypyc/codegen/emitmodule.py
@@ -56,6 +56,7 @@
 from mypyc.irbuild.prepare import load_type_map
 from mypyc.namegen import NameGenerator, exported_name
 from mypyc.options import CompilerOptions
+from mypyc.transform.copy_propagation import do_copy_propagation
 from mypyc.transform.exceptions import insert_exception_handling
 from mypyc.transform.refcount import insert_ref_count_opcodes
 from mypyc.transform.uninit import insert_uninit_checks
@@ -225,18 +226,16 @@ def compile_scc_to_ir(
     if errors.num_errors > 0:
         return modules
 
-    # Insert uninit checks.
     for module in modules.values():
         for fn in module.functions:
+            # Insert uninit checks.
             insert_uninit_checks(fn)
-    # Insert exception handling.
-    for module in modules.values():
-        for fn in module.functions:
+            # Insert exception handling.
             insert_exception_handling(fn)
-    # Insert refcount handling.
-    for module in modules.values():
-        for fn in module.functions:
+            # Insert refcount handling.
             insert_ref_count_opcodes(fn)
+            # Perform copy propagation optimization.
+            do_copy_propagation(fn, compiler_options)
 
     return modules
 
diff --git a/mypyc/irbuild/builder.py b/mypyc/irbuild/builder.py
index 9d160b08505d..4fe8e890a9c7 100644
--- a/mypyc/irbuild/builder.py
+++ b/mypyc/irbuild/builder.py
@@ -160,7 +160,7 @@ def __init__(
         options: CompilerOptions,
         singledispatch_impls: dict[FuncDef, list[RegisterImplInfo]],
     ) -> None:
-        self.builder = LowLevelIRBuilder(current_module, errors, mapper, options)
+        self.builder = LowLevelIRBuilder(errors, options)
         self.builders = [self.builder]
         self.symtables: list[dict[SymbolNode, SymbolTarget]] = [{}]
         self.runtime_args: list[list[RuntimeArg]] = [[]]
@@ -1111,9 +1111,7 @@ def flatten_classes(self, arg: RefExpr | TupleExpr) -> list[ClassIR] | None:
     def enter(self, fn_info: FuncInfo | str = "") -> None:
         if isinstance(fn_info, str):
             fn_info = FuncInfo(name=fn_info)
-        self.builder = LowLevelIRBuilder(
-            self.current_module, self.errors, self.mapper, self.options
-        )
+        self.builder = LowLevelIRBuilder(self.errors, self.options)
         self.builder.set_module(self.module_name, self.module_path)
         self.builders.append(self.builder)
         self.symtables.append({})
diff --git a/mypyc/irbuild/ll_builder.py b/mypyc/irbuild/ll_builder.py
index d1ea91476a66..45c06e11befd 100644
--- a/mypyc/irbuild/ll_builder.py
+++ b/mypyc/irbuild/ll_builder.py
@@ -126,7 +126,6 @@
     short_int_rprimitive,
     str_rprimitive,
 )
-from mypyc.irbuild.mapper import Mapper
 from mypyc.irbuild.util import concrete_arg_kind
 from mypyc.options import CompilerOptions
 from mypyc.primitives.bytes_ops import bytes_compare
@@ -220,12 +219,8 @@
 
 
 class LowLevelIRBuilder:
-    def __init__(
-        self, current_module: str, errors: Errors, mapper: Mapper, options: CompilerOptions
-    ) -> None:
-        self.current_module = current_module
+    def __init__(self, errors: Errors | None, options: CompilerOptions) -> None:
         self.errors = errors
-        self.mapper = mapper
         self.options = options
         self.args: list[Register] = []
         self.blocks: list[BasicBlock] = []
@@ -2394,6 +2389,7 @@ def _create_dict(self, keys: list[Value], values: list[Value], line: int) -> Val
             return self.call_c(dict_new_op, [], line)
 
     def error(self, msg: str, line: int) -> None:
+        assert self.errors is not None, "cannot generate errors in this compiler phase"
         self.errors.error(msg, self.module_path, line)
 
 
diff --git a/mypyc/test-data/opt-copy-propagation.test b/mypyc/test-data/opt-copy-propagation.test
new file mode 100644
index 000000000000..49b80f4385fc
--- /dev/null
+++ b/mypyc/test-data/opt-copy-propagation.test
@@ -0,0 +1,400 @@
+-- Test cases for copy propagation optimization.  This also tests IR transforms in general,
+-- as copy propagation was the first IR transform that was implemented.
+
+[case testCopyPropagationSimple]
+def g() -> int:
+    return 1
+
+def f() -> int:
+    y = g()
+    return y
+[out]
+def g():
+L0:
+    return 2
+def f():
+    r0 :: int
+L0:
+    r0 = g()
+    return r0
+
+[case testCopyPropagationChain]
+def f(x: int) -> int:
+    y = x
+    z = y
+    return z
+[out]
+def f(x):
+    x :: int
+L0:
+    return x
+
+[case testCopyPropagationChainPartial]
+def f(x: int) -> int:
+    y = x
+    z = y
+    x = 2
+    return z
+[out]
+def f(x):
+    x, y :: int
+L0:
+    y = x
+    x = 4
+    return y
+
+[case testCopyPropagationChainBad]
+def f(x: int) -> int:
+    y = x
+    z = y
+    y = 2
+    return z
+[out]
+def f(x):
+    x, y, z :: int
+L0:
+    y = x
+    z = y
+    y = 4
+    return z
+
+[case testCopyPropagationMutatedSource1]
+def f(x: int) -> int:
+    y = x
+    x = 1
+    return y
+[out]
+def f(x):
+    x, y :: int
+L0:
+    y = x
+    x = 2
+    return y
+
+[case testCopyPropagationMutatedSource2]
+def f() -> int:
+    z = 1
+    y = z
+    z = 2
+    return y
+[out]
+def f():
+    z, y :: int
+L0:
+    z = 2
+    y = z
+    z = 4
+    return y
+
+[case testCopyPropagationTooComplex]
+def f(b: bool, x: int) -> int:
+    if b:
+        y = x
+        return y
+    else:
+        y = 1
+        return y
+[out]
+def f(b, x):
+    b :: bool
+    x, y :: int
+L0:
+    if b goto L1 else goto L2 :: bool
+L1:
+    y = x
+    return y
+L2:
+    y = 2
+    return y
+
+[case testCopyPropagationArg]
+def f(x: int) -> int:
+    x = 2
+    return x
+[out]
+def f(x):
+    x :: int
+L0:
+    x = 4
+    return x
+
+[case testCopyPropagationPartiallyDefined1]
+def f(b: bool) -> int:
+    if b:
+        x = 1
+    y = x
+    return y
+[out]
+def f(b):
+    b :: bool
+    r0, x :: int
+    r1 :: bool
+    y :: int
+L0:
+    r0 = <error> :: int
+    x = r0
+    if b goto L1 else goto L2 :: bool
+L1:
+    x = 2
+L2:
+    if is_error(x) goto L3 else goto L4
+L3:
+    r1 = raise UnboundLocalError('local variable "x" referenced before assignment')
+    unreachable
+L4:
+    y = x
+    return y
+
+-- The remaining test cases test basic IRTransform functionality and are not
+-- all needed for testing copy propagation as such.
+
+[case testIRTransformBranch]
+from mypy_extensions import i64
+
+def f(x: bool) -> int:
+    y = x
+    if y:
+        return 1
+    else:
+        return 2
+[out]
+def f(x):
+    x :: bool
+L0:
+    if x goto L1 else goto L2 :: bool
+L1:
+    return 2
+L2:
+    return 4
+
+[case testIRTransformAssignment]
+def f(b: bool, x: int) -> int:
+    y = x
+    if b:
+        return y
+    else:
+        return 1
+[out]
+def f(b, x):
+    b :: bool
+    x :: int
+L0:
+    if b goto L1 else goto L2 :: bool
+L1:
+    return x
+L2:
+    return 2
+
+[case testIRTransformRegisterOps1]
+from __future__ import annotations
+from typing import cast
+
+class C:
+    a: int
+
+    def m(self, x: int) -> None: pass
+
+def get_attr(x: C) -> int:
+    y = x
+    return y.a
+
+def set_attr(x: C) -> None:
+    y = x
+    y.a = 1
+
+def tuple_get(x: tuple[int, int]) -> int:
+    y = x
+    return y[0]
+
+def tuple_set(x: int, xx: int) -> tuple[int, int]:
+    y = x
+    z = xx
+    return y, z
+
+def call(x: int) -> int:
+    y = x
+    return call(y)
+
+def method_call(c: C, x: int) -> None:
+    y = x
+    c.m(y)
+
+def cast_op(x: object) -> str:
+    y = x
+    return cast(str, y)
+
+def box(x: int) -> object:
+    y = x
+    return y
+
+def unbox(x: object) -> int:
+    y = x
+    return cast(int, y)
+
+def call_c(x: list[str]) -> None:
+    y = x
+    y.append("x")
+
+def keep_alive(x: C) -> int:
+    y = x
+    return y.a + 1
+[out]
+def C.m(self, x):
+    self :: __main__.C
+    x :: int
+L0:
+    return 1
+def get_attr(x):
+    x :: __main__.C
+    r0 :: int
+L0:
+    r0 = x.a
+    return r0
+def set_attr(x):
+    x :: __main__.C
+    r0 :: bool
+L0:
+    x.a = 2; r0 = is_error
+    return 1
+def tuple_get(x):
+    x :: tuple[int, int]
+    r0 :: int
+L0:
+    r0 = x[0]
+    return r0
+def tuple_set(x, xx):
+    x, xx :: int
+    r0 :: tuple[int, int]
+L0:
+    r0 = (x, xx)
+    return r0
+def call(x):
+    x, r0 :: int
+L0:
+    r0 = call(x)
+    return r0
+def method_call(c, x):
+    c :: __main__.C
+    x :: int
+    r0 :: None
+L0:
+    r0 = c.m(x)
+    return 1
+def cast_op(x):
+    x :: object
+    r0 :: str
+L0:
+    r0 = cast(str, x)
+    return r0
+def box(x):
+    x :: int
+    r0 :: object
+L0:
+    r0 = box(int, x)
+    return r0
+def unbox(x):
+    x :: object
+    r0 :: int
+L0:
+    r0 = unbox(int, x)
+    return r0
+def call_c(x):
+    x :: list
+    r0 :: str
+    r1 :: i32
+    r2 :: bit
+L0:
+    r0 = 'x'
+    r1 = PyList_Append(x, r0)
+    r2 = r1 >= 0 :: signed
+    return 1
+def keep_alive(x):
+    x :: __main__.C
+    r0, r1 :: int
+L0:
+    r0 = borrow x.a
+    r1 = CPyTagged_Add(r0, 2)
+    keep_alive x
+    return r1
+
+[case testIRTransformRegisterOps2]
+from mypy_extensions import i32, i64
+
+def truncate(x: i64) -> i32:
+    y = x
+    return i32(y)
+
+def extend(x: i32) -> i64:
+    y = x
+    return i64(y)
+
+def int_op(x: i64, xx: i64) -> i64:
+    y = x
+    z = xx
+    return y + z
+
+def comparison_op(x: i64, xx: i64) -> bool:
+    y = x
+    z = xx
+    return y == z
+
+def float_op(x: float, xx: float) -> float:
+    y = x
+    z = xx
+    return y + z
+
+def float_neg(x: float) -> float:
+    y = x
+    return -y
+
+def float_comparison_op(x: float, xx: float) -> bool:
+    y = x
+    z = xx
+    return y == z
+[out]
+def truncate(x):
+    x :: i64
+    r0 :: i32
+L0:
+    r0 = truncate x: i64 to i32
+    return r0
+def extend(x):
+    x :: i32
+    r0 :: i64
+L0:
+    r0 = extend signed x: i32 to i64
+    return r0
+def int_op(x, xx):
+    x, xx, r0 :: i64
+L0:
+    r0 = x + xx
+    return r0
+def comparison_op(x, xx):
+    x, xx :: i64
+    r0 :: bit
+L0:
+    r0 = x == xx
+    return r0
+def float_op(x, xx):
+    x, xx, r0 :: float
+L0:
+    r0 = x + xx
+    return r0
+def float_neg(x):
+    x, r0 :: float
+L0:
+    r0 = -x
+    return r0
+def float_comparison_op(x, xx):
+    x, xx :: float
+    r0 :: bit
+L0:
+    r0 = x == xx
+    return r0
+
+-- Note that transforms of these ops aren't tested here:
+-- * LoadMem
+-- * SetMem
+-- * GetElementPtr
+-- * LoadAddress
+-- * Unborrow
diff --git a/mypyc/test/test_copy_propagation.py b/mypyc/test/test_copy_propagation.py
new file mode 100644
index 000000000000..c729e3d186c3
--- /dev/null
+++ b/mypyc/test/test_copy_propagation.py
@@ -0,0 +1,47 @@
+"""Runner for copy propagation optimization tests."""
+
+from __future__ import annotations
+
+import os.path
+
+from mypy.errors import CompileError
+from mypy.test.config import test_temp_dir
+from mypy.test.data import DataDrivenTestCase
+from mypyc.common import TOP_LEVEL_NAME
+from mypyc.ir.pprint import format_func
+from mypyc.options import CompilerOptions
+from mypyc.test.testutil import (
+    ICODE_GEN_BUILTINS,
+    MypycDataSuite,
+    assert_test_output,
+    build_ir_for_single_file,
+    remove_comment_lines,
+    use_custom_builtins,
+)
+from mypyc.transform.copy_propagation import do_copy_propagation
+from mypyc.transform.uninit import insert_uninit_checks
+
+files = ["opt-copy-propagation.test"]
+
+
+class TestCopyPropagation(MypycDataSuite):
+    files = files
+    base_path = test_temp_dir
+
+    def run_case(self, testcase: DataDrivenTestCase) -> None:
+        with use_custom_builtins(os.path.join(self.data_prefix, ICODE_GEN_BUILTINS), testcase):
+            expected_output = remove_comment_lines(testcase.output)
+            try:
+                ir = build_ir_for_single_file(testcase.input)
+            except CompileError as e:
+                actual = e.messages
+            else:
+                actual = []
+                for fn in ir:
+                    if fn.name == TOP_LEVEL_NAME and not testcase.name.endswith("_toplevel"):
+                        continue
+                    insert_uninit_checks(fn)
+                    do_copy_propagation(fn, CompilerOptions())
+                    actual.extend(format_func(fn))
+
+            assert_test_output(testcase, actual, "Invalid source code output", expected_output)
diff --git a/mypyc/transform/copy_propagation.py b/mypyc/transform/copy_propagation.py
new file mode 100644
index 000000000000..49de616f85a3
--- /dev/null
+++ b/mypyc/transform/copy_propagation.py
@@ -0,0 +1,94 @@
+"""Simple copy propagation optimization.
+
+Example input:
+
+    x = f()
+    y = x
+
+The register x is redundant and we can directly assign its value to y:
+
+    y = f()
+
+This can optimize away registers that are assigned to once.
+"""
+
+from __future__ import annotations
+
+from mypyc.ir.func_ir import FuncIR
+from mypyc.ir.ops import Assign, AssignMulti, LoadAddress, LoadErrorValue, Register, Value
+from mypyc.irbuild.ll_builder import LowLevelIRBuilder
+from mypyc.options import CompilerOptions
+from mypyc.sametype import is_same_type
+from mypyc.transform.ir_transform import IRTransform
+
+
+def do_copy_propagation(fn: FuncIR, options: CompilerOptions) -> None:
+    """Perform copy propagation optimization for fn."""
+
+    # Anything with an assignment count >1 will not be optimized
+    # here, as it would be require data flow analysis and we want to
+    # keep this simple and fast, at least until we've made data flow
+    # analysis much faster.
+    counts: dict[Value, int] = {}
+    replacements: dict[Value, Value] = {}
+    for arg in fn.arg_regs:
+        # Arguments are always assigned to initially
+        counts[arg] = 1
+
+    for block in fn.blocks:
+        for op in block.ops:
+            if isinstance(op, Assign):
+                c = counts.get(op.dest, 0)
+                counts[op.dest] = c + 1
+                # Does this look like a supported assignment?
+                # TODO: Something needs LoadErrorValue assignments to be preserved?
+                if (
+                    c == 0
+                    and is_same_type(op.dest.type, op.src.type)
+                    and not isinstance(op.src, LoadErrorValue)
+                ):
+                    replacements[op.dest] = op.src
+                elif c == 1:
+                    # Too many assignments -- don't replace this one
+                    replacements.pop(op.dest, 0)
+            elif isinstance(op, AssignMulti):
+                # Copy propagation not supported for AssignMulti destinations
+                counts[op.dest] = 2
+                replacements.pop(op.dest, 0)
+            elif isinstance(op, LoadAddress):
+                # We don't support taking the address of an arbitrary Value,
+                # so we'll need to preserve the operands of LoadAddress.
+                if isinstance(op.src, Register):
+                    counts[op.src] = 2
+                    replacements.pop(op.src, 0)
+
+    # Follow chains of propagation with more than one assignment.
+    for src, dst in list(replacements.items()):
+        if counts.get(dst, 0) > 1:
+            # Not supported
+            del replacements[src]
+        else:
+            while dst in replacements:
+                dst = replacements[dst]
+                if counts.get(dst, 0) > 1:
+                    # Not supported
+                    del replacements[src]
+        if src in replacements:
+            replacements[src] = dst
+
+    builder = LowLevelIRBuilder(None, options)
+    transform = CopyPropagationTransform(builder, replacements)
+    transform.transform_blocks(fn.blocks)
+    fn.blocks = builder.blocks
+
+
+class CopyPropagationTransform(IRTransform):
+    def __init__(self, builder: LowLevelIRBuilder, map: dict[Value, Value]) -> None:
+        super().__init__(builder)
+        self.op_map.update(map)
+        self.removed = set(map)
+
+    def visit_assign(self, op: Assign) -> Value | None:
+        if op.dest in self.removed:
+            return None
+        return self.add(op)
diff --git a/mypyc/transform/ir_transform.py b/mypyc/transform/ir_transform.py
new file mode 100644
index 000000000000..1bcfc8fb5feb
--- /dev/null
+++ b/mypyc/transform/ir_transform.py
@@ -0,0 +1,353 @@
+"""Helpers for implementing generic IR to IR transforms."""
+
+from __future__ import annotations
+
+from typing import Final, Optional
+
+from mypyc.ir.ops import (
+    Assign,
+    AssignMulti,
+    BasicBlock,
+    Box,
+    Branch,
+    Call,
+    CallC,
+    Cast,
+    ComparisonOp,
+    DecRef,
+    Extend,
+    FloatComparisonOp,
+    FloatNeg,
+    FloatOp,
+    GetAttr,
+    GetElementPtr,
+    Goto,
+    IncRef,
+    InitStatic,
+    IntOp,
+    KeepAlive,
+    LoadAddress,
+    LoadErrorValue,
+    LoadGlobal,
+    LoadLiteral,
+    LoadMem,
+    LoadStatic,
+    MethodCall,
+    Op,
+    OpVisitor,
+    RaiseStandardError,
+    Return,
+    SetAttr,
+    SetMem,
+    Truncate,
+    TupleGet,
+    TupleSet,
+    Unborrow,
+    Unbox,
+    Unreachable,
+    Value,
+)
+from mypyc.irbuild.ll_builder import LowLevelIRBuilder
+
+
+class IRTransform(OpVisitor[Optional[Value]]):
+    """Identity transform.
+
+    Subclass and override to perform changes to IR.
+
+    Subclass IRTransform and override any OpVisitor visit_* methods
+    that perform any IR changes. The default implementations implement
+    an identity transform.
+
+    A visit method can return None to remove ops. In this case the
+    transform must ensure that no op uses the original removed op
+    as a source after the transform.
+
+    You can retain old BasicBlock and op references in ops. The transform
+    will automatically patch these for you as needed.
+    """
+
+    def __init__(self, builder: LowLevelIRBuilder) -> None:
+        self.builder = builder
+        # Subclasses add additional op mappings here. A None value indicates
+        # that the op/register is deleted.
+        self.op_map: dict[Value, Value | None] = {}
+
+    def transform_blocks(self, blocks: list[BasicBlock]) -> None:
+        """Transform basic blocks that represent a single function.
+
+        The result of the transform will be collected at self.builder.blocks.
+        """
+        block_map: dict[BasicBlock, BasicBlock] = {}
+        op_map = self.op_map
+        for block in blocks:
+            new_block = BasicBlock()
+            block_map[block] = new_block
+            self.builder.activate_block(new_block)
+            new_block.error_handler = block.error_handler
+            for op in block.ops:
+                new_op = op.accept(self)
+                if new_op is not op:
+                    op_map[op] = new_op
+
+        # Update all op/block references to point to the transformed ones.
+        patcher = PatchVisitor(op_map, block_map)
+        for block in self.builder.blocks:
+            for op in block.ops:
+                op.accept(patcher)
+            if block.error_handler is not None:
+                block.error_handler = block_map.get(block.error_handler, block.error_handler)
+
+    def add(self, op: Op) -> Value:
+        return self.builder.add(op)
+
+    def visit_goto(self, op: Goto) -> Value:
+        return self.add(op)
+
+    def visit_branch(self, op: Branch) -> Value:
+        return self.add(op)
+
+    def visit_return(self, op: Return) -> Value:
+        return self.add(op)
+
+    def visit_unreachable(self, op: Unreachable) -> Value:
+        return self.add(op)
+
+    def visit_assign(self, op: Assign) -> Value | None:
+        return self.add(op)
+
+    def visit_assign_multi(self, op: AssignMulti) -> Value | None:
+        return self.add(op)
+
+    def visit_load_error_value(self, op: LoadErrorValue) -> Value | None:
+        return self.add(op)
+
+    def visit_load_literal(self, op: LoadLiteral) -> Value | None:
+        return self.add(op)
+
+    def visit_get_attr(self, op: GetAttr) -> Value | None:
+        return self.add(op)
+
+    def visit_set_attr(self, op: SetAttr) -> Value | None:
+        return self.add(op)
+
+    def visit_load_static(self, op: LoadStatic) -> Value | None:
+        return self.add(op)
+
+    def visit_init_static(self, op: InitStatic) -> Value | None:
+        return self.add(op)
+
+    def visit_tuple_get(self, op: TupleGet) -> Value | None:
+        return self.add(op)
+
+    def visit_tuple_set(self, op: TupleSet) -> Value | None:
+        return self.add(op)
+
+    def visit_inc_ref(self, op: IncRef) -> Value | None:
+        return self.add(op)
+
+    def visit_dec_ref(self, op: DecRef) -> Value | None:
+        return self.add(op)
+
+    def visit_call(self, op: Call) -> Value | None:
+        return self.add(op)
+
+    def visit_method_call(self, op: MethodCall) -> Value | None:
+        return self.add(op)
+
+    def visit_cast(self, op: Cast) -> Value | None:
+        return self.add(op)
+
+    def visit_box(self, op: Box) -> Value | None:
+        return self.add(op)
+
+    def visit_unbox(self, op: Unbox) -> Value | None:
+        return self.add(op)
+
+    def visit_raise_standard_error(self, op: RaiseStandardError) -> Value | None:
+        return self.add(op)
+
+    def visit_call_c(self, op: CallC) -> Value | None:
+        return self.add(op)
+
+    def visit_truncate(self, op: Truncate) -> Value | None:
+        return self.add(op)
+
+    def visit_extend(self, op: Extend) -> Value | None:
+        return self.add(op)
+
+    def visit_load_global(self, op: LoadGlobal) -> Value | None:
+        return self.add(op)
+
+    def visit_int_op(self, op: IntOp) -> Value | None:
+        return self.add(op)
+
+    def visit_comparison_op(self, op: ComparisonOp) -> Value | None:
+        return self.add(op)
+
+    def visit_float_op(self, op: FloatOp) -> Value | None:
+        return self.add(op)
+
+    def visit_float_neg(self, op: FloatNeg) -> Value | None:
+        return self.add(op)
+
+    def visit_float_comparison_op(self, op: FloatComparisonOp) -> Value | None:
+        return self.add(op)
+
+    def visit_load_mem(self, op: LoadMem) -> Value | None:
+        return self.add(op)
+
+    def visit_set_mem(self, op: SetMem) -> Value | None:
+        return self.add(op)
+
+    def visit_get_element_ptr(self, op: GetElementPtr) -> Value | None:
+        return self.add(op)
+
+    def visit_load_address(self, op: LoadAddress) -> Value | None:
+        return self.add(op)
+
+    def visit_keep_alive(self, op: KeepAlive) -> Value | None:
+        return self.add(op)
+
+    def visit_unborrow(self, op: Unborrow) -> Value | None:
+        return self.add(op)
+
+
+class PatchVisitor(OpVisitor[None]):
+    def __init__(
+        self, op_map: dict[Value, Value | None], block_map: dict[BasicBlock, BasicBlock]
+    ) -> None:
+        self.op_map: Final = op_map
+        self.block_map: Final = block_map
+
+    def fix_op(self, op: Value) -> Value:
+        new = self.op_map.get(op, op)
+        assert new is not None, "use of removed op"
+        return new
+
+    def fix_block(self, block: BasicBlock) -> BasicBlock:
+        return self.block_map.get(block, block)
+
+    def visit_goto(self, op: Goto) -> None:
+        op.label = self.fix_block(op.label)
+
+    def visit_branch(self, op: Branch) -> None:
+        op.value = self.fix_op(op.value)
+        op.true = self.fix_block(op.true)
+        op.false = self.fix_block(op.false)
+
+    def visit_return(self, op: Return) -> None:
+        op.value = self.fix_op(op.value)
+
+    def visit_unreachable(self, op: Unreachable) -> None:
+        pass
+
+    def visit_assign(self, op: Assign) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_assign_multi(self, op: AssignMulti) -> None:
+        op.src = [self.fix_op(s) for s in op.src]
+
+    def visit_load_error_value(self, op: LoadErrorValue) -> None:
+        pass
+
+    def visit_load_literal(self, op: LoadLiteral) -> None:
+        pass
+
+    def visit_get_attr(self, op: GetAttr) -> None:
+        op.obj = self.fix_op(op.obj)
+
+    def visit_set_attr(self, op: SetAttr) -> None:
+        op.obj = self.fix_op(op.obj)
+        op.src = self.fix_op(op.src)
+
+    def visit_load_static(self, op: LoadStatic) -> None:
+        pass
+
+    def visit_init_static(self, op: InitStatic) -> None:
+        op.value = self.fix_op(op.value)
+
+    def visit_tuple_get(self, op: TupleGet) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_tuple_set(self, op: TupleSet) -> None:
+        op.items = [self.fix_op(item) for item in op.items]
+
+    def visit_inc_ref(self, op: IncRef) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_dec_ref(self, op: DecRef) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_call(self, op: Call) -> None:
+        op.args = [self.fix_op(arg) for arg in op.args]
+
+    def visit_method_call(self, op: MethodCall) -> None:
+        op.obj = self.fix_op(op.obj)
+        op.args = [self.fix_op(arg) for arg in op.args]
+
+    def visit_cast(self, op: Cast) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_box(self, op: Box) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_unbox(self, op: Unbox) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_raise_standard_error(self, op: RaiseStandardError) -> None:
+        if isinstance(op.value, Value):
+            op.value = self.fix_op(op.value)
+
+    def visit_call_c(self, op: CallC) -> None:
+        op.args = [self.fix_op(arg) for arg in op.args]
+
+    def visit_truncate(self, op: Truncate) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_extend(self, op: Extend) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_load_global(self, op: LoadGlobal) -> None:
+        pass
+
+    def visit_int_op(self, op: IntOp) -> None:
+        op.lhs = self.fix_op(op.lhs)
+        op.rhs = self.fix_op(op.rhs)
+
+    def visit_comparison_op(self, op: ComparisonOp) -> None:
+        op.lhs = self.fix_op(op.lhs)
+        op.rhs = self.fix_op(op.rhs)
+
+    def visit_float_op(self, op: FloatOp) -> None:
+        op.lhs = self.fix_op(op.lhs)
+        op.rhs = self.fix_op(op.rhs)
+
+    def visit_float_neg(self, op: FloatNeg) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_float_comparison_op(self, op: FloatComparisonOp) -> None:
+        op.lhs = self.fix_op(op.lhs)
+        op.rhs = self.fix_op(op.rhs)
+
+    def visit_load_mem(self, op: LoadMem) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_set_mem(self, op: SetMem) -> None:
+        op.dest = self.fix_op(op.dest)
+        op.src = self.fix_op(op.src)
+
+    def visit_get_element_ptr(self, op: GetElementPtr) -> None:
+        op.src = self.fix_op(op.src)
+
+    def visit_load_address(self, op: LoadAddress) -> None:
+        if isinstance(op.src, LoadStatic):
+            new = self.fix_op(op.src)
+            assert isinstance(new, LoadStatic)
+            op.src = new
+
+    def visit_keep_alive(self, op: KeepAlive) -> None:
+        op.src = [self.fix_op(s) for s in op.src]
+
+    def visit_unborrow(self, op: Unborrow) -> None:
+        op.src = self.fix_op(op.src)