Test, fix reductions with no inames

loopy/preprocess.py

@@ -1751,6 +1751,8 @@ def map_scan_local(expr, rec, callables_table, nresults, arg_dtypes,
 
     def map_reduction(expr, rec, callables_table,
                       guarding_predicates, nresults=1):
+        nonlocal made_changes
+
         # Only expand one level of reduction at a time, going from outermost to
         # innermost. Otherwise we get the (iname + insn) dependencies wrong.
 
@@ -1838,6 +1840,7 @@ def _error_if_force_scan_on(cls, msg):
             # to reduce over. It's rather similar to an array with () shape in
             # numpy.)
 
+            made_changes = True
             return expr.expr, callables_table
 
         # }}}
@@ -1866,6 +1869,7 @@ def _error_if_force_scan_on(cls, msg):
                              ", ".join(tag.key
                             for tag in temp_kernel.iname_tags(sweep_iname))))
                 elif parallel:
+                    made_changes = True
                     return map_scan_local(
                             expr, rec, callables_table, nresults,
                             arg_dtypes, reduction_dtypes,
@@ -1875,6 +1879,7 @@ def _error_if_force_scan_on(cls, msg):
                             scan_param.stride,
                             guarding_predicates)
                 elif sequential:
+                    made_changes = True
                     return map_scan_seq(
                             expr, rec, callables_table, nresults,
                             arg_dtypes, reduction_dtypes, sweep_iname,
@@ -1903,6 +1908,7 @@ def _error_if_force_scan_on(cls, msg):
                                      guarding_predicates)
         else:
             assert n_local_par > 0
+            made_changes = True
             return map_reduction_local(
                     expr, rec, callables_table, nresults, arg_dtypes,
                     reduction_dtypes, guarding_predicates)
@@ -1925,6 +1931,7 @@ def _error_if_force_scan_on(cls, msg):
         new_insn_add_within_inames = set()
 
         generated_insns = []
+        made_changes = False
 
         insn = insn_queue.pop(0)
 
@@ -1947,7 +1954,7 @@ def _error_if_force_scan_on(cls, msg):
                                         callables_table=cb_mapper.callables_table,
                                         guarding_predicates=insn.predicates),
 
-        if generated_insns:
+        if made_changes:
             # An expansion happened, so insert the generated stuff plus
             # ourselves back into the queue.
 

test/test_reduction.py

@@ -460,6 +460,25 @@ def test_any_all(ctx_factory):
     assert not out_dict["out2"].get()
 
 
+def test_reduction_without_inames(ctx_factory):
+    """Ensure that reductions with no inames get rewritten to the element
+    being reduced over. This was sometimes erroneously eliminated because
+    reduction realization used the generation of new statements as a criterion
+    for whether work was done.
+    """
+    ctx = ctx_factory()
+    cq = cl.CommandQueue(ctx)
+
+    knl = lp.make_kernel(
+            "{:}",
+            """
+            out = reduce(any, [], 5)
+            """)
+    knl = lp.set_options(knl, return_dict=True)
+
+    _, out_dict = knl(cq)
+
+
 if __name__ == "__main__":
     if len(sys.argv) > 1:
         exec(sys.argv[1])