More robust loop detection (#1646)

Generalizes the behavior of loop detection to support rotated loops,
single-state loops, and as a result LLVM canonical loops. The PR also
refactors the loop analysis methods and generalizes `DetectLoop`
transformation subclasses, such as `LoopToMap` and `LoopPeeling`.

dace/transformation/interstate/loop_peeling.py

@@ -79,17 +79,16 @@ def _modify_cond(self, condition, var, step):
     def apply(self, graph: ControlFlowRegion, sdfg: sd.SDFG):
         ####################################################################
         # Obtain loop information
-        guard: sd.SDFGState = self.loop_guard
         begin: sd.SDFGState = self.loop_begin
         after_state: sd.SDFGState = self.exit_state
 
         # Obtain iteration variable, range, and stride
-        condition_edge = graph.edges_between(guard, begin)[0]
-        not_condition_edge = graph.edges_between(guard, after_state)[0]
-        itervar, rng, loop_struct = find_for_loop(graph, guard, begin)
+        condition_edge = self.loop_condition_edge()
+        not_condition_edge = self.loop_exit_edge()
+        itervar, rng, loop_struct = self.loop_information()
 
         # Get loop states
-        loop_states = list(sdutil.dfs_conditional(graph, sources=[begin], condition=lambda _, child: child != guard))
+        loop_states = self.loop_body()
         first_id = loop_states.index(begin)
         last_state = loop_struct[1]
         last_id = loop_states.index(last_state)
@@ -104,7 +103,7 @@ def apply(self, graph: ControlFlowRegion, sdfg: sd.SDFG):
             init_edges = []
             before_states = loop_struct[0]
             for before_state in before_states:
-                init_edge = graph.edges_between(before_state, guard)[0]
+                init_edge = self.loop_init_edge()
                 init_edge.data.assignments[itervar] = str(rng[0] + self.count * rng[2])
                 init_edges.append(init_edge)
             append_states = before_states
@@ -133,7 +132,7 @@ def apply(self, graph: ControlFlowRegion, sdfg: sd.SDFG):
                 if append_state not in before_states:
                     for init_edge in init_edges:
                         graph.remove_edge(init_edge)
-                    graph.add_edge(append_state, guard, init_edges[0].data)
+                    graph.add_edge(append_state, init_edge.dst, init_edges[0].data)
         else:
             # If begin, change initialization assignment and prepend states before
             # guard
@@ -164,4 +163,4 @@ def apply(self, graph: ControlFlowRegion, sdfg: sd.SDFG):
             # Reconnect edge to guard state from last peeled iteration
             if prepend_state != after_state:
                 graph.remove_edge(not_condition_edge)
-                graph.add_edge(guard, prepend_state, not_condition_edge.data)
+                graph.add_edge(not_condition_edge.src, prepend_state, not_condition_edge.data)

dace/transformation/interstate/loop_to_map.py

@@ -95,15 +95,16 @@ def can_be_applied(self, graph: SDFGState, expr_index: int, sdfg: SDFG, permissi
         if not super().can_be_applied(graph, expr_index, sdfg, permissive):
             return False
 
-        guard = self.loop_guard
         begin = self.loop_begin
 
         # Guard state should not contain any dataflow
-        if len(guard.nodes()) != 0:
-            return False
+        if expr_index <= 1:
+            guard = self.loop_guard
+            if len(guard.nodes()) != 0:
+                return False
 
         # If loop cannot be detected, fail
-        found = find_for_loop(graph, guard, begin, itervar=self.itervar)
+        found = self.loop_information(itervar=self.itervar)
         if not found:
             return False
 
@@ -123,7 +124,7 @@ def can_be_applied(self, graph: SDFGState, expr_index: int, sdfg: SDFG, permissi
             return False
 
         # Find all loop-body states
-        states: List[SDFGState] = list(sdutil.dfs_conditional(sdfg, [begin], lambda _, c: c is not guard))
+        states: List[SDFGState] = self.loop_body()
 
         assert (body_end in states)
 
@@ -349,22 +350,15 @@ def apply(self, _, sdfg: sd.SDFG):
         from dace.sdfg.propagation import align_memlet
 
         # Obtain loop information
-        guard: sd.SDFGState = self.loop_guard
+        itervar, (start, end, step), (_, body_end) = self.loop_information(itervar=self.itervar)
+        states = self.loop_body()
         body: sd.SDFGState = self.loop_begin
-        after: sd.SDFGState = self.exit_state
-
-        # Obtain iteration variable, range, and stride
-        itervar, (start, end, step), (_, body_end) = find_for_loop(sdfg, guard, body, itervar=self.itervar)
-
-        # Find all loop-body states
-        states = set()
-        to_visit = [body]
-        while to_visit:
-            state = to_visit.pop(0)
-            for _, dst, _ in sdfg.out_edges(state):
-                if dst not in states and dst is not guard:
-                    to_visit.append(dst)
-            states.add(state)
+        exit_state = self.exit_state
+        entry_edge = self.loop_condition_edge()
+        init_edge = self.loop_init_edge()
+        after_edge = self.loop_exit_edge()
+        condition_edge = self.loop_condition_edge()
+        increment_edge = self.loop_increment_edge()
 
         nsdfg = None
 
@@ -425,7 +419,7 @@ def apply(self, _, sdfg: sd.SDFG):
             nsdfg = SDFG("loop_body", constants=sdfg.constants_prop, parent=new_body)
             nsdfg.add_node(body, is_start_state=True)
             body.parent = nsdfg
-            exit_state = nsdfg.add_state('exit')
+            nexit_state = nsdfg.add_state('exit')
             nsymbols = dict()
             for state in states:
                 if state is body:
@@ -438,20 +432,48 @@ def apply(self, _, sdfg: sd.SDFG):
                 for src, dst, data in sdfg.in_edges(state):
                     nsymbols.update({s: sdfg.symbols[s] for s in data.assignments.keys() if s in sdfg.symbols})
                     nsdfg.add_edge(src, dst, data)
-            nsdfg.add_edge(body_end, exit_state, InterstateEdge())
+            nsdfg.add_edge(body_end, nexit_state, InterstateEdge())
 
-            # Move guard -> body edge to guard -> new_body
-            for src, dst, data, in sdfg.edges_between(guard, body):
-                sdfg.add_edge(src, new_body, data)
-            # Move body_end -> guard edge to new_body -> guard
-            for src, dst, data in sdfg.edges_between(body_end, guard):
-                sdfg.add_edge(new_body, dst, data)
+            increment_edge = None
 
-            # Delete loop-body states and edges from parent SDFG
-            for state in states:
-                for e in sdfg.all_edges(state):
+            # Specific instructions for loop type
+            if self.expr_index <= 1:  # Natural loop with guard
+                guard = self.loop_guard
+
+                # Move guard -> body edge to guard -> new_body
+                for e in sdfg.edges_between(guard, body):
+                    sdfg.remove_edge(e)
+                    condition_edge = sdfg.add_edge(e.src, new_body, e.data)
+                # Move body_end -> guard edge to new_body -> guard
+                for e in sdfg.edges_between(body_end, guard):
                     sdfg.remove_edge(e)
-                sdfg.remove_node(state)
+                    increment_edge = sdfg.add_edge(new_body, e.dst, e.data)
+
+
+            elif 1 < self.expr_index <= 3:  # Rotated loop
+                entrystate = self.entry_state
+                latch = self.loop_latch
+
+                # Move entry edge to entry -> new_body
+                for src, dst, data, in sdfg.edges_between(entrystate, body):
+                    init_edge = sdfg.add_edge(src, new_body, data)
+
+                # Move body_end -> latch to new_body -> latch
+                for src, dst, data in sdfg.edges_between(latch, exit_state):
+                    after_edge = sdfg.add_edge(new_body, dst, data)
+
+            elif self.expr_index == 4:  # Self-loop
+                entrystate = self.entry_state
+
+                # Move entry edge to entry -> new_body
+                for src, dst, data in sdfg.edges_between(entrystate, body):
+                    init_edge = sdfg.add_edge(src, new_body, data)
+                for src, dst, data in sdfg.edges_between(body, exit_state):
+                    after_edge = sdfg.add_edge(new_body, dst, data)
+
+
+            # Delete loop-body states and edges from parent SDFG
+            sdfg.remove_nodes_from(states)
 
             # Add NestedSDFG arrays
             for name in read_set | write_set:
@@ -490,12 +512,13 @@ def apply(self, _, sdfg: sd.SDFG):
             # correct map with a positive increment
             start, end, step = end, start, -step
 
+        reentry_assignments = {k: v for k, v in condition_edge.data.assignments.items() if k != itervar}
+
         # If necessary, make a nested SDFG with assignments
-        isedge = sdfg.edges_between(guard, body)[0]
         symbols_to_remove = set()
-        if len(isedge.data.assignments) > 0:
+        if len(reentry_assignments) > 0:
             nsdfg = helpers.nest_state_subgraph(sdfg, body, gr.SubgraphView(body, body.nodes()))
-            for sym in isedge.data.free_symbols:
+            for sym in entry_edge.data.free_symbols:
                 if sym in nsdfg.symbol_mapping or sym in nsdfg.in_connectors:
                     continue
                 if sym in sdfg.symbols:
@@ -522,12 +545,12 @@ def apply(self, _, sdfg: sd.SDFG):
             nstate = nsdfg.sdfg.node(0)
             init_state = nsdfg.sdfg.add_state_before(nstate)
             nisedge = nsdfg.sdfg.edges_between(init_state, nstate)[0]
-            nisedge.data.assignments = isedge.data.assignments
+            nisedge.data.assignments = reentry_assignments
             symbols_to_remove = set(nisedge.data.assignments.keys())
             for k in nisedge.data.assignments.keys():
                 if k in nsdfg.symbol_mapping:
                     del nsdfg.symbol_mapping[k]
-            isedge.data.assignments = {}
+            condition_edge.data.assignments = {}
 
         source_nodes = body.source_nodes()
         sink_nodes = body.sink_nodes()
@@ -541,8 +564,8 @@ def apply(self, _, sdfg: sd.SDFG):
                     continue
                 # Arrays written with subsets that do not depend on the loop variable must be thread-local
                 map_dependency = False
-                for e in state.in_edges(node):
-                    subset = e.data.get_dst_subset(e, state)
+                for e in body.in_edges(node):
+                    subset = e.data.get_dst_subset(e, body)
                     if any(str(s) == itervar for s in subset.free_symbols):
                         map_dependency = True
                         break
@@ -644,25 +667,26 @@ def apply(self, _, sdfg: sd.SDFG):
         if not source_nodes and not sink_nodes:
             body.add_nedge(entry, exit, memlet.Memlet())
 
-        # Get rid of the loop exit condition edge
-        after_edge = sdfg.edges_between(guard, after)[0]
+        # Get rid of the loop exit condition edge (it will be readded below)
         sdfg.remove_edge(after_edge)
 
         # Remove the assignment on the edge to the guard
-        for e in sdfg.in_edges(guard):
+        for e in [init_edge, increment_edge]:
+            if e is None:
+                continue
             if itervar in e.data.assignments:
                 del e.data.assignments[itervar]
 
         # Remove the condition on the entry edge
-        condition_edge = sdfg.edges_between(guard, body)[0]
         condition_edge.data.condition = CodeBlock("1")
 
         # Get rid of backedge to guard
-        sdfg.remove_edge(sdfg.edges_between(body, guard)[0])
+        if increment_edge is not None:
+            sdfg.remove_edge(increment_edge)
 
         # Route body directly to after state, maintaining any other assignments
         # it might have had
-        sdfg.add_edge(body, after, sd.InterstateEdge(assignments=after_edge.data.assignments))
+        sdfg.add_edge(body, exit_state, sd.InterstateEdge(assignments=after_edge.data.assignments))
 
         # If this had made the iteration variable a free symbol, we can remove
         # it from the SDFG symbols

dace/transformation/interstate/loop_unroll.py

@@ -30,9 +30,7 @@ def can_be_applied(self, graph, expr_index, sdfg, permissive=False):
         if not super().can_be_applied(graph, expr_index, sdfg, permissive):
             return False
 
-        guard = self.loop_guard
-        begin = self.loop_begin
-        found = find_for_loop(graph, guard, begin)
+        found = self.loop_information()
 
         # If loop cannot be detected, fail
         if not found:
@@ -49,20 +47,19 @@ def can_be_applied(self, graph, expr_index, sdfg, permissive=False):
 
     def apply(self, graph: ControlFlowRegion, sdfg):
         # Obtain loop information
-        guard: sd.SDFGState = self.loop_guard
         begin: sd.SDFGState = self.loop_begin
         after_state: sd.SDFGState = self.exit_state
 
         # Obtain iteration variable, range, and stride, together with the last
         # state(s) before the loop and the last loop state.
-        itervar, rng, loop_struct = find_for_loop(graph, guard, begin)
+        itervar, rng, loop_struct = self.loop_information()
 
         # Loop must be fully unrollable for now.
         if self.count != 0:
             raise NotImplementedError  # TODO(later)
 
         # Get loop states
-        loop_states = list(sdutil.dfs_conditional(graph, sources=[begin], condition=lambda _, child: child != guard))
+        loop_states = self.loop_body()
         first_id = loop_states.index(begin)
         last_state = loop_struct[1]
         last_id = loop_states.index(last_state)
@@ -91,7 +88,7 @@ def apply(self, graph: ControlFlowRegion, sdfg):
             unrolled_states.append((new_states[first_id], new_states[last_id]))
 
         # Get any assignments that might be on the edge to the after state
-        after_assignments = (graph.edges_between(guard, after_state)[0].data.assignments)
+        after_assignments = self.loop_exit_edge().data.assignments
 
         # Connect new states to before and after states without conditions
         if unrolled_states:
@@ -101,7 +98,8 @@ def apply(self, graph: ControlFlowRegion, sdfg):
             graph.add_edge(unrolled_states[-1][1], after_state, sd.InterstateEdge(assignments=after_assignments))
 
         # Remove old states from SDFG
-        graph.remove_nodes_from([guard] + loop_states)
+        guard_or_latch = self.loop_meta_states()
+        graph.remove_nodes_from(guard_or_latch + loop_states)
 
     def instantiate_loop(
         self,

dace/transformation/interstate/move_loop_into_map.py

@@ -35,12 +35,10 @@ def can_be_applied(self, graph, expr_index, sdfg, permissive=False):
             return False
 
         # Obtain loop information
-        guard: sd.SDFGState = self.loop_guard
         body: sd.SDFGState = self.loop_begin
-        after: sd.SDFGState = self.exit_state
 
         # Obtain iteration variable, range, and stride
-        loop_info = find_for_loop(sdfg, guard, body)
+        loop_info = self.loop_information()
         if not loop_info:
             return False
         itervar, (start, end, step), (_, body_end) = loop_info
@@ -157,11 +155,10 @@ def test_subset_dependency(subset: sbs.Subset, mparams: Set[int]) -> Tuple[bool,
 
     def apply(self, _, sdfg: sd.SDFG):
         # Obtain loop information
-        guard: sd.SDFGState = self.loop_guard
         body: sd.SDFGState = self.loop_begin
 
         # Obtain iteration variable, range, and stride
-        itervar, (start, end, step), _ = find_for_loop(sdfg, guard, body)
+        itervar, (start, end, step), _ = self.loop_information()
 
         forward_loop = step > 0
 
@@ -194,26 +191,31 @@ def apply(self, _, sdfg: sd.SDFG):
             else:
                 guard_body_edge = e
 
-        for body_inedge in sdfg.in_edges(body):
-            if body_inedge.src is guard:
-                guard_body_edge.data.assignments.update(body_inedge.data.assignments)
-            sdfg.remove_edge(body_inedge)
-        for body_outedge in sdfg.out_edges(body):
-            sdfg.remove_edge(body_outedge)
-        for guard_inedge in sdfg.in_edges(guard):
-            before_guard_edge.data.assignments.update(guard_inedge.data.assignments)
-            guard_inedge.data.assignments = {}
-            sdfg.add_edge(guard_inedge.src, body, guard_inedge.data)
-            sdfg.remove_edge(guard_inedge)
-        for guard_outedge in sdfg.out_edges(guard):
-            if guard_outedge.dst is body:
-                guard_body_edge.data.assignments.update(guard_outedge.data.assignments)
-            else:
-                guard_after_edge.data.assignments.update(guard_outedge.data.assignments)
-            guard_outedge.data.condition = CodeBlock("1")
-            sdfg.add_edge(body, guard_outedge.dst, guard_outedge.data)
-            sdfg.remove_edge(guard_outedge)
-        sdfg.remove_node(guard)
+        if self.expr_index <= 1:
+            guard = self.loop_guard
+            for body_inedge in sdfg.in_edges(body):
+                if body_inedge.src is guard:
+                    guard_body_edge.data.assignments.update(body_inedge.data.assignments)
+                sdfg.remove_edge(body_inedge)
+            for body_outedge in sdfg.out_edges(body):
+                sdfg.remove_edge(body_outedge)
+            for guard_inedge in sdfg.in_edges(guard):
+                before_guard_edge.data.assignments.update(guard_inedge.data.assignments)
+                guard_inedge.data.assignments = {}
+                sdfg.add_edge(guard_inedge.src, body, guard_inedge.data)
+                sdfg.remove_edge(guard_inedge)
+            for guard_outedge in sdfg.out_edges(guard):
+                if guard_outedge.dst is body:
+                    guard_body_edge.data.assignments.update(guard_outedge.data.assignments)
+                else:
+                    guard_after_edge.data.assignments.update(guard_outedge.data.assignments)
+                guard_outedge.data.condition = CodeBlock("1")
+                sdfg.add_edge(body, guard_outedge.dst, guard_outedge.data)
+                sdfg.remove_edge(guard_outedge)
+            sdfg.remove_node(guard)
+        else:  # Rotated or self loops
+            raise NotImplementedError('MoveLoopIntoMap not implemented for rotated and self-loops')
+
         if itervar in nsdfg.symbol_mapping:
             del nsdfg.symbol_mapping[itervar]
         if itervar in sdfg.symbols: