[Mlir-commits] [mlir] [mlir] [linalg] Add pattern to swap transpose with broadcast (PR #97063)

[Mehdi Amini]

================
@@ -51,6 +56,60 @@ Some important things to think about w.r.t. canonicalization patterns:
 *   It is always good to eliminate operations entirely when possible, e.g. by
     folding known identities (like "x + 0 = x").
 
+*   Canonicalize isn't a great place to put pattens with expensive compile time
+    (i.e. have O(n) complexity) or complicated cost models.
+
+*   Canonicalize shouldn't drop the semantic of original operation.
+
+For example, a pattern that transform
+
+```
+  %res = vector.transpose %0, [1, 0] : vector<nx1x<eltty>> to vector<1xnx<elty>>
+```
+
+to
+
+```
+  %res = vector.shape_cast %0 : vector<nx1x<eltty>> to vector<1xnx<elty>>
+```
+
+is not a good canonicalize pattern because it drops the transpose semantic.
----------------
joker-eph wrote:

This is a bit vague of an example, if we want to go there we should find a more obvious example to explain I think.

https://github.com/llvm/llvm-project/pull/97063