[mypyc] Provide an easier way to define IR-to-IR transforms (#16998)

This makes it easy to define simple IR-to-IR transforms by subclassing
`IRTansform` and overriding some visit methods.

Add an implementation of a simple copy propagation optimization as an
example.

This will be used by the implementation of mypyc/mypyc#854, and this can
also be used for various optimizations.

The IR transform preserves the identities of ops that are not modified.
This means that the old IR is no longer valid after the transform, but
the transform can be fast since we don't need to allocate many objects
if only a small subset of ops will be modified by a transform.

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
 

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({})

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)