[flang] [llvm] [mlir] [flang][OpenMP] Enable tiling (PR #143715)

[Sergio Afonso via llvm-commits]

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@@ -614,13 +614,19 @@ def WorkshareLoopWrapperOp : OpenMP_Op<"workshare.loop_wrapper", traits = [
 def LoopNestOp : OpenMP_Op<"loop_nest", traits = [
     RecursiveMemoryEffects, SameVariadicOperandSize
   ], clauses = [
-    OpenMP_LoopRelatedClause
+    OpenMP_CollapseClause,
+    OpenMP_LoopRelatedClause,
+    OpenMP_TileSizesClause
   ], singleRegion = true> {
   let summary = "rectangular loop nest";
   let description = [{
-    This operation represents a collapsed rectangular loop nest. For each
-    rectangular loop of the nest represented by an instance of this operation,
-    lower and upper bounds, as well as a step variable, must be defined.
+    This operation represents a rectangular loop nest which may be collapsed
+    and/or tiled. For each rectangular loop of the nest represented by an
+    instance of this operation, lower and upper bounds, as well as a step
+    variable, must be defined. The collapse clause specifies how many loops
+    that should be collapsed (1 if no collapse is done) after any tiling is
+    performed. The tiling sizes is represented by the tile sizes clause.
+
----------------
skatrak wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/143715