From be94a8b07c5901c11a328295a78e1de1373737c7 Mon Sep 17 00:00:00 2001
From: Sebastien Bourdeauducq <sb@m-labs.hk>
Date: Wed, 29 Oct 2014 18:46:06 +0800
Subject: [PATCH] transforms/fold_constants: support comparisons

---
 artiq/transforms/fold_constants.py | 38 ++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/artiq/transforms/fold_constants.py b/artiq/transforms/fold_constants.py
index 1258796f4..ff9aac9ca 100644
--- a/artiq/transforms/fold_constants.py
+++ b/artiq/transforms/fold_constants.py
@@ -28,6 +28,14 @@ _ast_binops = {
     ast.BitAnd: operator.and_
 }
 
+_ast_cmpops = {
+    ast.Eq: operator.eq,
+    ast.NotEq: operator.ne,
+    ast.Lt: operator.lt,
+    ast.LtE: operator.le,
+    ast.Gt: operator.gt,
+    ast.GtE: operator.ge
+}
 
 _ast_boolops = {
     ast.Or: lambda x, y: x or y,
@@ -68,6 +76,36 @@ class _ConstantFolder(ast.NodeTransformer):
             return node
         return ast.copy_location(result, node)
 
+    def visit_Compare(self, node):
+        self.generic_visit(node)
+        try:
+            operands = [eval_constant(node.left)]
+        except NotConstant:
+            operands = [node.left]
+        ops = []
+        for op, right_ast in zip(node.ops, node.comparators):
+            try:
+                right = eval_constant(right_ast)
+            except NotConstant:
+                right = right_ast
+            if (not isinstance(operands[-1], ast.AST)
+                    and not isinstance(right, ast.AST)):
+                left = operands.pop()
+                operands.append(_ast_cmpops[type(op)](left, right))
+            else:
+                ops.append(op)
+                operands.append(right_ast)
+        operands = [operand if isinstance(operand, ast.AST)
+                    else ast.copy_location(value_to_ast(operand), node)
+                    for operand in operands]
+        if len(operands) == 1:
+            return operands[0]
+        else:
+            node.left = operands[0]
+            node.right = operands[1:]
+            node.ops = ops
+            return node
+
     def visit_BoolOp(self, node):
         self.generic_visit(node)
         new_values = []