diff --git a/loopy/preprocess.py b/loopy/preprocess.py
index 2f19e7e3e850daf8f982cbc3a1c3194ddbec53fd..db7792cce55c9b7851850c3059e821fc574c3270 100644
--- a/loopy/preprocess.py
+++ b/loopy/preprocess.py
@@ -746,7 +746,8 @@ def find_idempotence(kernel):
for var in reads_map[insn.id]
for writer_id in writer_map.get(var, set()))
- # Find SCCs of dep_graph.
+ # Find SCCs of dep_graph. These are used for checking if the instruction is
+ # in a dependency cycle.
from loopy.tools import compute_sccs
sccs = dict((item, scc)
diff --git a/loopy/tools.py b/loopy/tools.py
index 7952b875a6b1ce4a7a8cac587eaf2abc16eed8d3..01d0641fc25c11a092185125604613819a0293ca 100644
--- a/loopy/tools.py
+++ b/loopy/tools.py
@@ -291,48 +291,49 @@ def compute_sccs(graph):
while to_search:
top = next(iter(to_search))
- stack = [top]
+ call_stack = [(top, iter(graph[top]), None)]
+ visit_stack = []
visiting = set()
scc = []
- while stack:
- top = stack[-1]
+ while call_stack:
+ top, children, last_popped_child = call_stack.pop()
- if top in visiting:
- for child in graph[top]:
- if child in visiting:
- # Update SCC root.
- scc_root[top] = min(
- scc_root[top],
- scc_root[child])
-
- # Add to the current SCC and check if we're the root.
- scc.append(top)
-
- if visit_order[top] == scc_root[top]:
- sccs.append(scc)
- scc = []
-
- to_search.discard(top)
- visiting.remove(top)
-
- if top in visit_order:
- stack.pop()
- else:
+ if top not in visiting:
+ # Unvisited: mark as visited, initialize SCC root.
count = len(visit_order)
+ visit_stack.append(top)
visit_order[top] = count
scc_root[top] = count
visiting.add(top)
+ to_search.discard(top)
- for child in graph[top]:
- if child in visiting:
- # Update SCC root.
- scc_root[top] = min(
- scc_root[top],
- visit_order[child])
- elif child not in visit_order:
- stack.append(child)
+ # Returned from a recursion, update SCC.
+ if last_popped_child is not None:
+ scc_root[top] = min(
+ scc_root[top],
+ scc_root[last_popped_child])
+
+ for child in children:
+ if child not in visit_order:
+ # Recurse.
+ call_stack.append((top, children, child))
+ call_stack.append((child, iter(graph[child]), None))
+ break
+ if child in visiting:
+ scc_root[top] = min(
+ scc_root[top],
+ visit_order[child])
+ else:
+ if scc_root[top] == visit_order[top]:
+ scc = []
+ while visit_stack[-1] != top:
+ scc.append(visit_stack.pop())
+ scc.append(visit_stack.pop())
+ for item in scc:
+ visiting.remove(item)
+ sccs.append(scc)
return sccs
diff --git a/loopy/type_inference.py b/loopy/type_inference.py
index 851a8d2a2a048e4b0fc3b87ce9d730dc49ff70af..6b5c77de349dbc1ea594c57f0f9b868b76df62e4 100644
--- a/loopy/type_inference.py
+++ b/loopy/type_inference.py
@@ -511,9 +511,9 @@ def infer_unknown_types(kernel, expect_completion=False):
from loopy.tools import compute_sccs
# To speed up processing, we sort the variables by computing the SCCs of the
- # type dependency graph. Each SCC represents a set of variables whose type
- # mutually depends on themselves. The SCCs are returned in topological
- # order.
+ # type dependency graph. Each SCC represents a set of variables whose types
+ # mutually depend on themselves. The SCCs are returned and processed in
+ # topological order.
sccs = compute_sccs(dep_graph)
item_lookup = _DictUnionView([
@@ -529,17 +529,18 @@ def infer_unknown_types(kernel, expect_completion=False):
from loopy.kernel.data import TemporaryVariable, KernelArgument
- failed_names = set()
for var_chain in sccs:
changed_during_last_queue_run = False
queue = var_chain[:]
+ failed_names = set()
while queue or changed_during_last_queue_run:
if not queue and changed_during_last_queue_run:
changed_during_last_queue_run = False
- # Optimization: If there's a single variable in the SCC and
- # the type of variable does not depend on itself, then
- # the type is known after a single iteration.
+ # Optimization: If there's a single variable in the SCC without
+ # a self-referential dependency, then the type is known after a
+ # single iteration (we don't need to look at the expressions
+ # again).
if len(var_chain) == 1:
single_var, = var_chain
if single_var not in dep_graph[single_var]:
diff --git a/test/test_misc.py b/test/test_misc.py
new file mode 100644
index 0000000000000000000000000000000000000000..aa6a2cd075e6dd69d5c92118032672f2a334a492
--- /dev/null
+++ b/test/test_misc.py
@@ -0,0 +1,79 @@
+from __future__ import division, absolute_import, print_function
+
+__copyright__ = "Copyright (C) 2016 Matt Wala"
+
+__license__ = """
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
+"""
+
+import six # noqa
+from six.moves import range
+
+import sys
+
+import logging
+logger = logging.getLogger(__name__)
+
+
+def test_compute_sccs():
+ from loopy.tools import compute_sccs
+ import random
+
+ rng = random.Random(0)
+
+ def generate_random_graph(nnodes):
+ graph = dict((i, set()) for i in range(nnodes))
+ for i in range(nnodes):
+ for j in range(nnodes):
+ # Edge probability 1/n: Generates decently interesting inputs.
+ if rng.randint(0, nnodes - 1) == 0:
+ graph[i].add(j)
+ return graph
+
+ def verify_sccs(graph, sccs):
+ visited = set()
+
+ def visit(node):
+ if node in visited:
+ return []
+ else:
+ visited.add(node)
+ result = []
+ for child in graph[node]:
+ result = result + visit(child)
+ return result + [node]
+
+ for scc in sccs:
+ result = visit(scc[0])
+ assert set(result) == set(scc), (set(result), set(scc))
+
+ for nnodes in range(10, 20):
+ for i in range(40):
+ graph = generate_random_graph(nnodes)
+ verify_sccs(graph, compute_sccs(graph))
+
+
+if __name__ == "__main__":
+ if len(sys.argv) > 1:
+ exec(sys.argv[1])
+ else:
+ from py.test.cmdline import main
+ main([__file__])
+
+# vim: foldmethod=marker