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 insn_changed
+
         # Only expand one level of reduction at a time, going from outermost to
         # innermost. Otherwise we get the (iname + insn) dependencies wrong.
 
@@ -1827,6 +1829,10 @@ def _error_if_force_scan_on(cls, msg):
                        ", ".join(str(kernel.iname_tags(iname))
                                  for iname in bad_inames)))
 
+        # }}}
+
+        insn_changed = True
+
         if n_local_par == 0 and n_sequential == 0:
             from loopy.diagnostic import warn_with_kernel
             warn_with_kernel(kernel, "empty_reduction",
@@ -1840,8 +1846,6 @@ def _error_if_force_scan_on(cls, msg):
 
             return expr.expr, callables_table
 
-        # }}}
-
         if may_be_implemented_as_scan:
             assert force_scan or automagic_scans_ok
 
@@ -1916,7 +1920,7 @@ def _error_if_force_scan_on(cls, msg):
     domains = kernel.domains[:]
 
     temp_kernel = kernel
-    changed = False
+    kernel_changed = False
 
     import loopy as lp
     while insn_queue:
@@ -1925,6 +1929,7 @@ def _error_if_force_scan_on(cls, msg):
         new_insn_add_within_inames = set()
 
         generated_insns = []
+        insn_changed = False
 
         insn = insn_queue.pop(0)
 
@@ -1947,7 +1952,7 @@ def _error_if_force_scan_on(cls, msg):
                                         callables_table=cb_mapper.callables_table,
                                         guarding_predicates=insn.predicates),
 
-        if generated_insns:
+        if insn_changed:
             # An expansion happened, so insert the generated stuff plus
             # ourselves back into the queue.
 
@@ -2010,14 +2015,14 @@ def _error_if_force_scan_on(cls, msg):
                     domains=domains)
             temp_kernel = lp.replace_instruction_ids(
                     temp_kernel, insn_id_replacements)
-            changed = True
+            kernel_changed = True
         else:
             # nothing happened, we're done with insn
             assert not new_insn_add_depends_on
 
             new_insns.append(insn)
 
-    if changed:
+    if kernel_changed:
         kernel = kernel.copy(
             instructions=new_insns,
             temporary_variables=new_temporary_variables,

test/test_reduction.py

@@ -460,6 +460,27 @@ 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)
+
+    assert out_dict["out"].get() == 5
+
+
 if __name__ == "__main__":
     if len(sys.argv) > 1:
         exec(sys.argv[1])