From 4da8668971c10f28d63d805e306306db6f1985b4 Mon Sep 17 00:00:00 2001
From: Kaushik Kulkarni <kaushikcfd@gmail.com>
Date: Wed, 7 Oct 2020 23:31:18 -0500
Subject: [PATCH] account for 0-long arrays

---
 pytato/codegen.py   |  8 +++++++-
 test/test_pytato.py | 11 +++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/pytato/codegen.py b/pytato/codegen.py
index 496b176..fe9075a 100644
--- a/pytato/codegen.py
+++ b/pytato/codegen.py
@@ -639,7 +639,13 @@ def domain_for_shape(dim_names: Tuple[str, ...],
         dom &= aff_from_expr(dom.space, left).le_set(affs[iname])
         dom &= affs[iname].lt_set(aff_from_expr(dom.space, right))
 
-    dom, = dom.get_basic_sets()
+    doms = dom.get_basic_sets()
+
+    if len(doms) == 0:
+        # empty set
+        dom = isl.BasicSet.empty(dom.get_space())
+    else:
+        dom, = doms
 
     return dom
 
diff --git a/test/test_pytato.py b/test/test_pytato.py
index 76e11ef..1923807 100755
--- a/test/test_pytato.py
+++ b/test/test_pytato.py
@@ -125,6 +125,17 @@ def test_make_placeholder_noname():
     assert x.name in knl.get_read_variables()
 
 
+def test_zero_length_arrays():
+    ns = pt.Namespace()
+    x = pt.make_placeholder(ns, shape=(0, 4), dtype=float)
+    y = 2*x
+
+    assert y.shape == (0, 4)
+
+    knl = pt.generate_loopy(y).program
+    assert all(dom.is_empty() for dom in knl.domains if dom.total_dim() != 0)
+
+
 if __name__ == "__main__":
     if len(sys.argv) > 1:
         exec(sys.argv[1])
-- 
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