Lunderberg commented on code in PR #16596:
URL: https://github.com/apache/tvm/pull/16596#discussion_r1500745301


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src/relax/transform/reorder_permute_dims_after_concat.cc:
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@@ -0,0 +1,173 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ * \file tvm/relax/transform/reorder_permute_dims_after_concat.cc
+ * \brief Reorder concat(permute_dims(A), permute_dims(B)) into 
permute_dims(concat(A,B))
+ */
+
+#include <tvm/relax/analysis.h>
+#include <tvm/relax/dataflow_matcher.h>
+#include <tvm/relax/expr.h>
+#include <tvm/relax/expr_functor.h>
+#include <tvm/relax/transform.h>
+
+#include <optional>
+#include <unordered_set>
+#include <vector>
+
+#include "../op/tensor/index.h"
+#include "../op/tensor/linear_algebra.h"
+#include "../op/tensor/manipulate.h"
+
+namespace tvm {
+namespace relax {
+
+namespace {
+std::tuple<DFPattern, TypedPackedFunc<Expr(Expr, Map<DFPattern, Expr>)>> 
CreatePatterns() {
+  // TODO(Lunderberg): Allow pattern-matching to handle a flexible
+  // number of arguments, each of which matches the same type of
+  // pattern.
+  size_t min_concat = 2;
+  size_t max_concat = 12;

Review Comment:
   Yeah.  If the number of concat parameters is exceeded, then the match 
silently fails.  And unlike `CombineParallelMatmul`, which could be run 
repeatedly if the number of concatenations is exceeded, the validity checking 
for reordering requires all concatenated tensors before performing any change.
   
   Long-term, I think the flexible tuple index will be the way to go.  I think 
it will end up needing explicit tuple extent variables.  That way, a pattern 
containing two flexible tuple extents could distinguish between a single shared 
extent and two independent extents.  I'm picturing something like the following:
   
   ```c++
   // A normal wildcard argument
   DFWildcard arg;
   
   // Represents the extent of the tuple containing a flexible pattern.
   DFArbitraryExtent tuple_extent;
   
   // A pattern that may have a different value within each element of the 
tuple.
   DFRepeatedPattern args(arg, tuple_extent);
   
   // The DFRepeatedPattern could be used to build up additional patterns
   DFCallPattern transposed_args(OpPattern("relax.permute_dims"), args);
   
   // Eventually, a pattern match for a tuple of unknown length gets 
instantiated.
   DFArbitraryTuplePattern concat_tuple(transposed_args, tuple_extent);
   
   // Which could then be used to match operators whose arguments are an 
   // arbitrary tuple length.
   DFCallPattern concat_pat(OpPattern("relax.concat"), concat_tuple);
   ```
   
   But that's for brainstorming an implementation that would be much later down 
the road.



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