From 6400e28e4ccfd65c617822ec6f803666e649b4cb Mon Sep 17 00:00:00 2001
From: Sebastien Bourdeauducq <sb@m-labs.hk>
Date: Sat, 21 Jun 2014 00:19:56 +0200
Subject: [PATCH] compiler: fold constants

---
 artiq/compiler/fold_constants.py | 85 ++++++++++++++++++++++++++++++++
 artiq/devices/core.py            |  3 ++
 2 files changed, 88 insertions(+)
 create mode 100644 artiq/compiler/fold_constants.py

diff --git a/artiq/compiler/fold_constants.py b/artiq/compiler/fold_constants.py
new file mode 100644
index 000000000..2dbcf835e
--- /dev/null
+++ b/artiq/compiler/fold_constants.py
@@ -0,0 +1,85 @@
+import ast, operator
+
+from artiq.language import units
+from artiq.compiler.tools import value_to_ast
+
+class _NotConstant(Exception):
+	pass
+
+def _get_constant(node):
+	if isinstance(node, ast.Num):
+		return node.n
+	elif isinstance(node, ast.Str):
+		return node.s
+	elif isinstance(node, ast.Call) \
+	  and isinstance(node.func, ast.Name) \
+	  and node.func.id == "Quantity":
+		amount, unit = node.args
+		amount = _get_constant(amount)
+		try:
+			unit = getattr(units, unit.id)
+		except:
+			raise _NotConstant
+		return units.Quantity(amount, unit)
+	else:
+		raise _NotConstant
+
+_ast_unops = {
+	ast.Invert: operator.inv,
+	ast.Not: operator.not_,
+	ast.UAdd: operator.pos,
+	ast.USub: operator.neg
+}
+
+_ast_binops = {
+	ast.Add: operator.add,
+	ast.Sub: operator.sub,
+	ast.Mult: operator.mul,
+	ast.Div: operator.truediv,
+	ast.FloorDiv: operator.floordiv,
+	ast.Mod: operator.mod,
+	ast.Pow: operator.pow,
+	ast.LShift: operator.lshift,
+	ast.RShift: operator.rshift,
+	ast.BitOr: operator.or_,
+	ast.BitXor: operator.xor,
+	ast.BitAnd: operator.and_
+}
+
+class _ConstantFolder(ast.NodeTransformer):
+	def visit_UnaryOp(self, node):
+		self.generic_visit(node)
+		try:
+			operand = _get_constant(node.operand)
+		except _NotConstant:
+			return node
+		try:
+			op = _ast_unops[type(node.op)]
+		except KeyError:
+			return node
+		try:
+			result = value_to_ast(op(operand))
+		except:
+			return node
+		return result
+
+	def visit_BinOp(self, node):
+		self.generic_visit(node)
+		try:
+			left, right = _get_constant(node.left), _get_constant(node.right)
+		except _NotConstant:
+			return node
+		try:
+			op = _ast_binops[type(node.op)]
+		except KeyError:
+			return node
+		try:
+			result = value_to_ast(op(left, right))
+		except:
+			return node
+		return result
+
+def fold_constants(stmts):
+	constant_folder = _ConstantFolder()
+	new_stmts = [constant_folder.visit(stmt) for stmt in stmts]
+	stmts[:] = new_stmts
diff --git a/artiq/devices/core.py b/artiq/devices/core.py
index 66eb365ab..ca225520a 100644
--- a/artiq/devices/core.py
+++ b/artiq/devices/core.py
@@ -1,11 +1,14 @@
 from operator import itemgetter
 
 from artiq.compiler.inline import inline
+from artiq.compiler.fold_constants import fold_constants
 from artiq.compiler.unparse import Unparser
 
 class Core:
 	def run(self, k_function, k_args, k_kwargs):
 		stmts, rpc_map = inline(self, k_function, k_args, k_kwargs)
+		fold_constants(stmts)
+
 
 		print("=========================")
 		print(" Inlined")