transforms: add dead code removal

artiq/coredevice/core.py

@@ -4,6 +4,7 @@ from artiq.transforms.inline import inline
 from artiq.transforms.lower_units import lower_units
 from artiq.transforms.remove_inter_assigns import remove_inter_assigns
 from artiq.transforms.fold_constants import fold_constants
+from artiq.transforms.remove_dead_code import remove_dead_code
 from artiq.transforms.unroll_loops import unroll_loops
 from artiq.transforms.interleave import interleave
 from artiq.transforms.lower_time import lower_time
@@ -43,7 +44,7 @@ class Core:
 
     def run(self, k_function, k_args, k_kwargs):
         # transform/simplify AST
-        _debug_unparse = _make_debug_unparse("fold_constants_2")
+        _debug_unparse = _make_debug_unparse("remove_dead_code")
 
         func_def, rpc_map, exception_map = inline(
             self, k_function, k_args, k_kwargs)
@@ -75,6 +76,9 @@ class Core:
         fold_constants(func_def)
         _debug_unparse("fold_constants_2", func_def)
 
+        remove_dead_code(func_def)
+        _debug_unparse("remove_dead_code", func_def)
+
         # compile to machine code and run
         binary = get_runtime_binary(self.runtime_env, func_def)
         self.core_com.load(binary)

artiq/transforms/remove_dead_code.py

@@ -0,0 +1,57 @@
+import ast
+
+from artiq.transforms.tools import is_replaceable
+
+
+class _SourceLister(ast.NodeVisitor):
+    def __init__(self):
+        self.sources = set()
+
+    def visit_Name(self, node):
+        if isinstance(node.ctx, ast.Load):
+            self.sources.add(node.id)
+
+
+class _DeadCodeRemover(ast.NodeTransformer):
+    def __init__(self, kept_targets):
+        self.kept_targets = kept_targets
+
+    def visit_Assign(self, node):
+        new_targets = []
+        for target in node.targets:
+            if not (isinstance(target, ast.Name)
+                    and target.id not in self.kept_targets):
+                new_targets.append(target)
+        if not new_targets and is_replaceable(node.value):
+            return None
+        else:
+            return node
+
+    def visit_AugAssign(self, node):
+        if (isinstance(node.target, ast.Name)
+                and node.target.id not in self.kept_targets
+                and is_replaceable(node.value)):
+            return None
+        else:
+            return node
+
+    def visit_If(self, node):
+        if isinstance(node.test, ast.NameConstant):
+            if node.test.value:
+                return node.body
+            else:
+                return node.orelse
+        else:
+            return node
+
+    def visit_While(self, node):
+        if isinstance(node.test, ast.NameConstant) and not node.test.value:
+            return node.orelse
+        else:
+            return node
+
+
+def remove_dead_code(func_def):
+    sl = _SourceLister()
+    sl.visit(func_def)
+    _DeadCodeRemover(sl.sources).visit(func_def)

artiq/transforms/remove_inter_assigns.py

@@ -1,24 +1,7 @@
 import ast
 from copy import copy, deepcopy
 
-
-_replaceable_funcs = {
-    "bool", "int", "float", "round",
-    "int64", "round64", "Fraction",
-}
-
-
-def _is_replaceable(value):
-    if isinstance(value, (ast.NameConstant, ast.Num, ast.Str)):
-        return True
-    elif isinstance(value, ast.BinOp):
-        return _is_replaceable(value.left) and _is_replaceable(value.right)
-    elif isinstance(value, ast.BoolOp):
-        return all(_is_replaceable(v) for v in value.values)
-    elif isinstance(value, ast.Call) and isinstance(value.func, ast.Name):
-        return value.func.id in _replaceable_funcs
-    else:
-        return False
+from artiq.transforms.tools import is_replaceable
 
 
 class _TargetLister(ast.NodeVisitor):
@@ -47,7 +30,7 @@ class _InterAssignRemover(ast.NodeTransformer):
 
     def visit_Assign(self, node):
         self.generic_visit(node)
-        if _is_replaceable(node.value):
+        if is_replaceable(node.value):
             for target in node.targets:
                 if isinstance(target, ast.Name):
                     self.replacements[target.id] = node.value

artiq/transforms/tools.py

@@ -75,3 +75,23 @@ def eval_constant(node):
             raise NotConstant
     else:
         raise NotConstant
+
+
+_replaceable_funcs = {
+    "bool", "int", "float", "round",
+    "int64", "round64", "Fraction",
+    "Quantity"
+}
+
+
+def is_replaceable(expr):
+    if isinstance(expr, (ast.NameConstant, ast.Num, ast.Str)):
+        return True
+    elif isinstance(expr, ast.BinOp):
+        return is_replaceable(expr.left) and is_replaceable(expr.right)
+    elif isinstance(expr, ast.BoolOp):
+        return all(is_replaceable(v) for v in expr.values)
+    elif isinstance(expr, ast.Call) and isinstance(expr.func, ast.Name):
+        return expr.func.id in _replaceable_funcs
+    else:
+        return False