[mlir][mesh] In sharding attr use FlatSymbolRefAttr instead of SymbolRefAttr (#76886)

Analogous to func.call use FlatSymbolRefAttr to reference the
corresponding mesh.

Author: sogartar

mlir/include/mlir/Dialect/Mesh/IR/MeshBase.td

@@ -79,7 +79,7 @@ def MeshSharding : AttrDef<Mesh_Dialect, "MeshSharding"> {
   let mnemonic = "shard";
 
   let parameters = (ins
-    AttrParameter<"::mlir::SymbolRefAttr", "cluster placed">:$cluster,
+    AttrParameter<"::mlir::FlatSymbolRefAttr", "cluster placed">:$cluster,
     ArrayRefParameter<"MeshAxesAttr">:$split_axes,
     OptionalArrayRefParameter<"MeshAxis">:$partial_axes,
     OptionalParameter<"::mlir::mesh::Partial">:$partial_type
@@ -91,7 +91,7 @@ def MeshSharding : AttrDef<Mesh_Dialect, "MeshSharding"> {
     The MeshSharding attribute could be used in the encoding of a
     `RankedTensorType` or the mesh.shard op. it contains three sub-attributes:
 
-    1. `cluster`: this attribute is a SymbolRefAttr that refers to the mesh
+    1. `cluster`: this attribute is a FlatSymbolRefAttr that refers to the mesh
     cluster where the distributed tensor is placed. The symbol must resolve to a
     `mesh.cluster` operation.
 
@@ -145,7 +145,7 @@ def MeshSharding : AttrDef<Mesh_Dialect, "MeshSharding"> {
   }];
 
   let builders = [
-    AttrBuilder<(ins "SymbolRefAttr":$cluster, 
+    AttrBuilder<(ins "FlatSymbolRefAttr":$cluster,
                      "ArrayRef<SmallVector<MeshAxis>>":$split_axes,
                      "ArrayRef<MeshAxis>": $partial_axes,
                      "mesh::Partial": $partial_type), [{
@@ -156,7 +156,7 @@ def MeshSharding : AttrDef<Mesh_Dialect, "MeshSharding"> {
       return $_get($_ctxt, cluster, splitAxesAttr, partial_axes,
                    partial_type);
     }]>,
-    AttrBuilder<(ins "SymbolRefAttr":$cluster, 
+    AttrBuilder<(ins "FlatSymbolRefAttr":$cluster,
                      "ArrayRef<SmallVector<MeshAxis>>":$split_axes), [{
       return MeshShardingAttr::get($_ctxt, cluster, split_axes, {}, Partial::Sum);
     }]>

mlir/include/mlir/Dialect/Mesh/IR/MeshOps.td

@@ -196,12 +196,12 @@ def Mesh_ShardOp : Mesh_Op<"shard", [Pure, SameOperandsAndResultType]> {
     ```
   }];
   let arguments = (ins
-    Builtin_RankedTensor:$src,
+    AnyRankedTensor:$src,
     MeshSharding:$shard,
     UnitAttr:$annotate_for_users
   );
   let results = (outs
-    Builtin_RankedTensor:$result
+    AnyRankedTensor:$result
   );
   let assemblyFormat = [{
     $src `to` $shard (`annotate_for_users` $annotate_for_users^)? attr-dict `:`

mlir/include/mlir/Dialect/Mesh/Interfaces/ShardingInterface.h

@@ -25,13 +25,13 @@ struct ShardingOption {
   // An array of int array. The sub-array at the i-th position signifies the
   // mesh axes the i-th loop will be sharded on.
   ShardingArray shardingArray = {};
-  SymbolRefAttr cluster = nullptr;
+  FlatSymbolRefAttr cluster = nullptr;
   // `empty` being true indicates that no sharding information can be inferred
   // at present. Note that it is different from the case where an operation is
   // not sharded.
   bool empty = false;
   ShardingOption() = default;
-  ShardingOption(ShardingArray shardingArray, SymbolRefAttr cluster)
+  ShardingOption(ShardingArray shardingArray, FlatSymbolRefAttr cluster)
       : shardingArray(std::move(shardingArray)), cluster(cluster) {}
 };
 

mlir/lib/Dialect/Mesh/IR/MeshOps.cpp

@@ -266,7 +266,7 @@ void ClusterShapeOp::build(OpBuilder &odsBuilder, OperationState &odsState,
 
 LogicalResult
 MeshShardingAttr::verify(function_ref<InFlightDiagnostic()> emitError,
-                         SymbolRefAttr, ArrayRef<MeshAxesAttr> splitAxes,
+                         FlatSymbolRefAttr, ArrayRef<MeshAxesAttr> splitAxes,
                          ArrayRef<MeshAxis> partialAxes, Partial) {
   // TODO: At present cluster symbol ref is not verified. This is due to the
   // difficulty in fetching the corresponding symbol op based on an attribute.

mlir/lib/Dialect/Mesh/Interfaces/ShardingInterface.cpp

@@ -215,7 +215,7 @@ namespace {
 // Update the given `shardingOption` according to `meshAxes` and `loopIdx`
 static LogicalResult fillShardingOption(Operation *op,
                                         ShardingOption &shardingOption,
-                                        SymbolRefAttr cluster,
+                                        FlatSymbolRefAttr cluster,
                                         ArrayRef<MeshAxis> meshAxes,
                                         unsigned loopIdx) {
   if ((shardingOption.cluster && cluster &&

mlir/test/Dialect/Mesh/invalid.mlir

@@ -70,6 +70,14 @@ func.func @mesh_axis_negtive_in_partial(
 
 // -----
 
+func.func @sharding_attribute_invalid_nested_symbol(%arg0 : tensor<4x8xf32>) {
+  // expected-error@+2 {{custom op 'mesh.shard' invalid kind of attribute specified}}
+  // expected-error@+1 {{custom op 'mesh.shard' failed to parse MeshSharding parameter 'cluster' which is to be a `::mlir::FlatSymbolRefAttr`}}
+  %0 = mesh.shard %arg0 to <@a::@b, [[0]]> : tensor<4x8xf32>
+}
+
+// -----
+
 mesh.cluster @mesh0(rank = 2, dim_sizes = 2x4)
 
 func.func @cluster_shape_mesh_axis_out_of_bounds() -> (index, index) {