New and Improved MapFusion (#1629)

This PR introduces a new and improved version of `MapFusion`.
A summary of the changes can also be found
[here](https://github.com/user-attachments/files/18516299/new_map_fusion_summary_of_changes.pdf),
it compares the resulting SDFGs generated by the old and new
transformation of some unit tests.

#### Fixed Bugs and removed Limitations
- The subsets (not the `.subset` member of the Memlet; I mean the
concept) of the new intermediate data descriptor were not computed
correctly in some cases, especially in presence of offsets. See the
`test_offset_correction_range_read()`,
`test_offset_correction_scalar_read()` and the
`test_offset_correction_empty()` tests.
- Upon the propagation of the subsets, due to the changed intermediate,
was not handled properly. Essentially, the transformation only updated
`.subset` and ignored `.other_subset`. Which is correct in most cases
but not always. See the `test_fusion_intrinsic_memlet_direction()` for
more.
- During the check if two maps could be fused the `.dynamic` property of
the Memelts were fully ignored leading to wrong code.
- The read-write conflict checks were refined, before all arrays needed
to be accessed the wrong way, i.e. before a fusion was rejected when one
map accessed `A[i, j]` and the other map was accessing `B[i + 1, j]`.
Now this is possible as long as every access is point wise. See the
`test_fusion_different_global_accesses()` test for an example.
- The shape of the reduced intermediate is cleaned, i.e. unnecessary
dimensions of size 1, are removed, except they were present in the
original shape. To make an example, the intermediate array, `T`, had
shape `(10, 1, 20)` and inside the map was accessed `T[__i, 0, __j]`,
then the old transformation would have created an reduced intermediate
of shape `(1, 1, 1)`, new its shape is `(1)`. Note if the intermediate
has shape `(10, 20)` instead and would be accessed as `T[__i, __j]` then
a `Scalar` would have been created. See also the `struct_dataflow` flag
below.

#### New Flags
- `only_toplevel_maps`: If `True` the transformation will only fuse maps
that are located at the top level, i.e. maps inside maps will not be
merged.
- `only_inner_maps`: If `True` then the transformation will only fuse
maps that are inside other maps.
- assume_always_shared`: If `True` then the transformation will assume
that every intermediate is shared, i.e. the referenced data is used
somewhere else in the SDFG and has to become an output of the fused
maps. This will create dead data flow, but avoids a scan of the full
SDFG.
- `strict_dataflow`: This flag is enabled by default. It has two
effects, first it will disable the cleaning of reduced intermediate
storage. The second effect is more important as it will preserve a much
stricter data flow. Most importantly, if the intermediate array is used
downstream (this is not limited to the case that the array is the output
of the second map) then the maps will not be fused together. This is
mostly to work around some other bugs in DaCe, where other
transformations failed to pink up the dependency. Note that the fused
map would be correct, the problem are other transformations.

#### `FullMapFusion`
This PR also introduced the `FullMapFusion` pass, which makes use of the
`FindSingleUseData` pass that was introduced in
[PR#1906](#1906).
The `FullMapFusion` applies MapFusion as long as possible, i.e. fuses
all maps that can be fused.
But instead of scanning the SDFG every time an intermediate node has to
be classified, i.e. can it be deleted or not, it is done once and then
reused which will speed up fusion process as it will remove the need to
traverse the full SDFG many times.
This new pass also replaced the direct application of MapFusion in
`auto_optimizer`.


#### References
Collection of known issues in other transformation:
- [RedundantArrayRemoval (auto
optimize)](#1644)
- [Bug in `RefineNestedAccess` and
`SDFGState._read_and_write_sets()](#1643)
- [Error in Composite Fusion (auto
optimize)](#1642)

---------

Co-authored-by: Philipp Schaad <[email protected]>

Author: philip-paul-mueller

.gitignore

@@ -192,3 +192,9 @@ _build/
 
 .*cache/
 /doc/source/config_schema.rst
+
+# Ignoring the test junk
+_all_tests/
+
+
+

dace/subsets.py

@@ -80,7 +80,7 @@ def covers(self, other):
         # Subsets of different dimensionality can never cover each other.
         if self.dims() != other.dims():
             return ValueError(
-                    f"A subset of dimensionality {self.dim()} cannot test covering a subset of dimensionality {other.dims()}"
+                    f"A subset of dimensionality {self.dims()} cannot test covering a subset of dimensionality {other.dims()}"
             )
 
         if not Config.get('optimizer', 'symbolic_positive'):
@@ -106,7 +106,7 @@ def covers_precise(self, other):
         # Subsets of different dimensionality can never cover each other.
         if self.dims() != other.dims():
             return ValueError(
-                    f"A subset of dimensionality {self.dim()} cannot test covering a subset of dimensionality {other.dims()}"
+                    f"A subset of dimensionality {self.dims()} cannot test covering a subset of dimensionality {other.dims()}"
             )
 
         # If self does not cover other with a bounding box union, return false.

dace/transformation/auto/auto_optimize.py

@@ -14,11 +14,12 @@
 import warnings
 
 # Transformations
-from dace.transformation.dataflow import MapCollapse, TrivialMapElimination, MapFusion, ReduceExpansion
+from dace.transformation.passes import FullMapFusion
+from dace.transformation.dataflow import MapCollapse, TrivialMapElimination, ReduceExpansion
 from dace.transformation.interstate import LoopToMap, RefineNestedAccess
 from dace.transformation.subgraph.composite import CompositeFusion
 from dace.transformation.subgraph import helpers as xfsh
-from dace.transformation import helpers as xfh
+from dace.transformation import helpers as xfh, pass_pipeline as ppl
 
 # Environments
 from dace.libraries.blas.environments import intel_mkl as mkl, openblas
@@ -57,8 +58,13 @@ def greedy_fuse(graph_or_subgraph: GraphViewType,
         if isinstance(graph_or_subgraph, SDFG):
             # If we have an SDFG, recurse into graphs
             graph_or_subgraph.simplify(validate_all=validate_all)
-            # MapFusion for trivial cases
-            graph_or_subgraph.apply_transformations_repeated(MapFusion, validate_all=validate_all)
+            # Apply MapFusion for the more trivial cases
+            full_map_fusion_pass = FullMapFusion(
+                    strict_dataflow=True,
+                    validate_all=validate_all,
+            )
+            full_map_fusion_pileline = ppl.Pipeline([full_map_fusion_pass])
+            full_map_fusion_pileline.apply_pass(graph_or_subgraph, {})
 
         # recurse into graphs
         for graph in graph_or_subgraph.nodes():
@@ -76,7 +82,13 @@ def greedy_fuse(graph_or_subgraph: GraphViewType,
         sdfg, graph, subgraph = None, None, None
         if isinstance(graph_or_subgraph, SDFGState):
             sdfg = graph_or_subgraph.parent
-            sdfg.apply_transformations_repeated(MapFusion, validate_all=validate_all)
+            # Apply MapFusion for the more trivial cases
+            full_map_fusion_pass = FullMapFusion(
+                    strict_dataflow=True,
+                    validate_all=validate_all,
+            )
+            full_map_fusion_pileline = ppl.Pipeline([full_map_fusion_pass])
+            full_map_fusion_pileline.apply_pass(sdfg, {})
             graph = graph_or_subgraph
             subgraph = SubgraphView(graph, graph.nodes())
         else:

dace/transformation/dataflow/buffer_tiling.py

@@ -98,7 +98,13 @@ def apply(self, graph, sdfg):
 
         # Fuse maps
         some_buffer = next(iter(buffers))  # some dummy to pass to MapFusion.apply_to()
-        MapFusion.apply_to(sdfg, first_map_exit=tile_map1_exit, array=some_buffer, second_map_entry=tile_map2_entry)
+        MapFusion.apply_to(
+                sdfg,
+                first_map_exit=tile_map1_exit,
+                array=some_buffer,
+                second_map_entry=tile_map2_entry,
+                verify=True,
+        )
 
         # Optimize the simple cases
         map1_entry.range.ranges = [