diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2c6c77e77..234988280 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -7,6 +7,10 @@ on:
     schedule:
         - cron:  '17 3 * * 0'
 
+concurrency:
+    group: ${{ github.head_ref || github.ref_name }}
+    cancel-in-progress: true
+
 jobs:
     ruff:
         name: Ruff
diff --git a/loopy/codegen/loop.py b/loopy/codegen/loop.py
index 645a57e31..c64c2ea67 100644
--- a/loopy/codegen/loop.py
+++ b/loopy/codegen/loop.py
@@ -28,6 +28,7 @@
 from loopy.codegen.control import build_loop_nest
 from loopy.codegen.result import merge_codegen_results
 from loopy.diagnostic import LoopyError, warn
+from loopy.symbolic import flatten
 
 
 # {{{ conditional-reducing slab decomposition
@@ -309,7 +310,7 @@ def set_up_hw_parallel_loops(codegen_state, schedule_index, next_func,
     codegen_state = codegen_state.intersect(slab)
 
     from loopy.symbolic import pw_aff_to_expr
-    hw_axis_expr = hw_axis_expr + pw_aff_to_expr(lower_bound)
+    hw_axis_expr = flatten(hw_axis_expr + pw_aff_to_expr(lower_bound))
 
     # }}}
 
diff --git a/loopy/expression.py b/loopy/expression.py
index 224521b03..2581ec022 100644
--- a/loopy/expression.py
+++ b/loopy/expression.py
@@ -23,7 +23,7 @@
 
 import numpy as np
 
-from pymbolic.mapper import RecursiveMapper
+from pymbolic.mapper import Mapper
 
 from loopy.codegen import UnvectorizableError
 from loopy.diagnostic import LoopyError
@@ -55,7 +55,7 @@ def dtype_to_type_context(target, dtype):
 
 # {{{ vectorizability checker
 
-class VectorizabilityChecker(RecursiveMapper):
+class VectorizabilityChecker(Mapper):
     """The return value from this mapper is a :class:`bool` indicating whether
     the result of the expression is vectorized along :attr:`vec_iname`.
     If the expression is not vectorizable, the mapper raises
diff --git a/loopy/symbolic.py b/loopy/symbolic.py
index 22dbd3bf5..6727423a8 100644
--- a/loopy/symbolic.py
+++ b/loopy/symbolic.py
@@ -54,6 +54,7 @@
 )
 from pymbolic.mapper.dependency import CachedDependencyMapper as DependencyMapperBase
 from pymbolic.mapper.evaluator import CachedEvaluationMapper as EvaluationMapperBase
+from pymbolic.mapper.flattener import FlattenMapper as FlattenMapperBase
 from pymbolic.mapper.stringifier import StringifyMapper as StringifyMapperBase
 from pymbolic.mapper.substitutor import (
     CachedSubstitutionMapper as SubstitutionMapperBase,
@@ -195,6 +196,14 @@ def map_resolved_function(self, expr, *args, **kwargs):
     map_fortran_division = IdentityMapperBase.map_quotient
 
 
+class FlattenMapper(FlattenMapperBase, IdentityMapperMixin):
+    pass
+
+
+def flatten(expr: ExpressionT) -> ExpressionT:
+    return FlattenMapper()(expr)
+
+
 class IdentityMapper(IdentityMapperBase, IdentityMapperMixin):
     pass
 
@@ -1833,7 +1842,7 @@ def aff_to_expr(aff: isl.Aff) -> ExpressionT:
         if coeff:
             result += coeff*aff_to_expr(aff.get_div(i))
 
-    return result // denom
+    return flatten(result // denom)
 
 
 def pw_aff_to_expr(pw_aff: isl.PwAff, int_ok: bool = False) -> ExpressionT:
@@ -2178,14 +2187,17 @@ def qpolynomial_to_expr(qpoly):
     assert all(isinstance(num, int) for num in numerators)
     assert isinstance(common_denominator, int)
 
+    # FIXME: Delete if in favor of the general case once we depend on pymbolic 2024.1.
     if common_denominator == 1:
-        return sum(num * monomial
+        res = sum(num * monomial
                    for num, monomial in zip(numerators, monomials))
     else:
-        return FloorDiv(sum(num * monomial
+        res = FloorDiv(sum(num * monomial
                             for num, monomial in zip(numerators, monomials)),
                         common_denominator)
 
+    return flatten(res)
+
 # }}}
 
 
diff --git a/loopy/target/c/codegen/expression.py b/loopy/target/c/codegen/expression.py
index 276407fc1..810ac4379 100644
--- a/loopy/target/c/codegen/expression.py
+++ b/loopy/target/c/codegen/expression.py
@@ -28,7 +28,7 @@
 import islpy as isl
 import pymbolic.primitives as p
 from pymbolic import var
-from pymbolic.mapper import IdentityMapper, RecursiveMapper
+from pymbolic.mapper import IdentityMapper, Mapper
 from pymbolic.mapper.stringifier import (
     PREC_BITWISE_AND,
     PREC_BITWISE_OR,
@@ -124,9 +124,8 @@ def wrap_in_typecast(self, actual_type: LoopyType, needed_type: LoopyType, s):
 
         return s
 
-    def rec(self, expr, type_context=None, needed_type: Optional[LoopyType] = None):
-        result = RecursiveMapper.rec(self, expr, type_context)
-
+    def rec(self, expr, type_context=None, needed_type: Optional[LoopyType] = None):  # type: ignore[override]
+        result = Mapper.rec(self, expr, type_context)
         if needed_type is None:
             return result
         else:
@@ -604,7 +603,7 @@ def map_nan(self, expr, type_context):
 
 # {{{ C expression to code mapper
 
-class CExpressionToCodeMapper(RecursiveMapper):
+class CExpressionToCodeMapper(Mapper):
 
     # {{{ helpers