diff --git a/grudge/symbolic/compiler.py b/grudge/symbolic/compiler.py
index 4a58961b66966485294092ba9baa60476b209afd..972e4056729808778e5875ba786ef25c1348f362 100644
--- a/grudge/symbolic/compiler.py
+++ b/grudge/symbolic/compiler.py
@@ -405,7 +405,12 @@ class Code(object):
 
             for dep in insn.get_dependencies():
                 try:
-                    writer = var_to_writer[dep.name]
+                    if isinstance(dep, Subscript):
+                        dep_name = dep.aggregate.name
+                    else:
+                        dep_name = dep.name
+
+                    writer = var_to_writer[dep_name]
                 except KeyError:
                     # input variables won't be found
                     pass
@@ -604,6 +609,11 @@ def aggregate_assignments(inf_mapper, instructions, result,
     # {{{ aggregation helpers
 
     def get_complete_origins_set(insn, skip_levels=0):
+        try:
+            return insn_to_origins_cache[insn]
+        except KeyError:
+            pass
+
         if skip_levels < 0:
             skip_levels = 0
 
@@ -617,6 +627,8 @@ def aggregate_assignments(inf_mapper, instructions, result,
                     result |= get_complete_origins_set(
                             dep_origin, skip_levels-1)
 
+        insn_to_origins_cache[insn] = result
+
         return result
 
     var_assignees_cache = {}
@@ -646,6 +658,8 @@ def aggregate_assignments(inf_mapper, instructions, result,
 
     # {{{ main aggregation pass
 
+    insn_to_origins_cache = {}
+
     origins_map = dict(
                 (assignee, insn)
                 for insn in instructions
diff --git a/grudge/symbolic/mappers/__init__.py b/grudge/symbolic/mappers/__init__.py
index 2b0b2242de11e6180d7889a2ec87a3b9e18a08f7..c2fba3d6a757fa9ed80babf4f7315707bf4e7858 100644
--- a/grudge/symbolic/mappers/__init__.py
+++ b/grudge/symbolic/mappers/__init__.py
@@ -933,9 +933,13 @@ class QuadratureCheckerAndRemover(CSECachingMapperMixin, IdentityMapper):
 # {{{ simplification / optimization
 
 class ConstantToNumpyConversionMapper(
+        CSECachingMapperMixin,
         pymbolic.mapper.constant_converter.ConstantToNumpyConversionMapper,
         IdentityMapperMixin):
-    pass
+    map_common_subexpression_uncached = (
+            pymbolic.mapper.constant_converter
+            .ConstantToNumpyConversionMapper
+            .map_common_subexpression)
 
 
 class CommutativeConstantFoldingMapper(