compiler: Fix printer for unevaluation Mul for issue 2577

Author: ZoeLeibowitz

devito/ir/cgen/printer.py

@@ -223,7 +223,7 @@ def _print_Mod(self, expr):
         return '%'.join(args)
 
     def _print_Mul(self, expr):
-        args = [a for a in expr.args if a != -1]
+        args = [a for a in expr.args if (a != -1. or a != -1)]
         neg = (len(expr.args) - len(args)) % 2
 
         if len(args) > 1:

tests/test_symbolics.py

@@ -15,6 +15,7 @@
                               INT, FieldFromComposite, IntDiv, Namespace, Rvalue,
                               ReservedWord, ListInitializer, uxreplace,
                               retrieve_derivatives, BaseCast)
+from devito.symbolics.unevaluation import Mul
 from devito.tools import as_tuple
 from devito.types import (Array, Bundle, FIndexed, LocalObject, Object,
                           ComponentAccess, StencilDimension, Symbol as dSymbol)
@@ -858,3 +859,12 @@ def test_assumptions(self, op, expr, assumptions, expected):
         assumptions = eval(assumptions)
         expected = eval(expected)
         assert evalrel(op, eqn, assumptions) == expected
+
+
+def test_issue_2577():
+
+    u = TimeFunction(name='u', grid=Grid((2,)))
+    eq = Eq(u.forward, Mul(-1, -1., u))
+    op = Operator(eq)
+
+    assert '--' not in str(op.ccode)