Initial commit: add .gitignore and README

.venv/lib/python3.12/site-packages/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)