[mlir][tensor][bufferize] Improve bufferization of DimOp/RankOp

[springerm]

Summary

The tensor operands do not bufferize to a memory read.

mlir/lib/Dialect/Tensor/Transforms/BufferizableOpInterfaceImpl.cpp

 };
 
 /// Bufferization of tensor.dim. Replace with memref.dim.
 struct DimOpInterface
     : public BufferizableOpInterface::ExternalModel<DimOpInterface,
                                                     tensor::DimOp> {
   bool bufferizesToMemoryRead(Operation *op, OpOperand &opOperand,
                               const AnalysisState &state) const {
-    return true;
+    // The op reads the tensor's metadata but not its contents.
+    return false;
   }
 
   bool bufferizesToMemoryWrite(Operation *op, OpOperand &opOperand,
                                const AnalysisState &state) const {
     return false;
   }
 
   SmallVector<OpResult> getAliasingOpResult(Operation *op, OpOperand &opOperand,

 };
 
 /// Bufferization of tensor.rank. Replace with memref.rank.
 struct RankOpInterface
     : public BufferizableOpInterface::ExternalModel<RankOpInterface,
                                                     tensor::RankOp> {
   bool bufferizesToMemoryRead(Operation *op, OpOperand &opOperand,
                               const AnalysisState &state) const {
-    return true;
+    // The op reads the tensor's metadata but not its contents.
+    return false;
   }
 
   bool bufferizesToMemoryWrite(Operation *op, OpOperand &opOperand,
                                const AnalysisState &state) const {
     return false;
   }
 
   SmallVector<OpResult> getAliasingOpResult(Operation *op, OpOperand &opOperand,

mlir/test/Dialect/Tensor/one-shot-bufferize.mlir

func.func @insert_slice_full_overwrite(%t: tensor<10xf32>, %b: tensor<10xf32>) -> tensor<10xf32> {
   %vec = vector.transfer_read %1[%c0], %cst : tensor<10xf32>, vector<10xf32>
   vector.print %vec : vector<10xf32>
 
   // Write back a different value (not %1).
   // CHECK: memref.copy %[[b]], %[[t]]
   %2 = tensor.insert_slice %b into %t[0][10][1] : tensor<10xf32> into tensor<10xf32>
   return %2 : tensor<10xf32>
 }
+
+// -----
+
+// CHECK-LABEL: func @dim_not_reading(
+//  CHECK-SAME:     %[[t:.*]]: memref<?xf32
+func.func @dim_not_reading(%t: tensor<?xf32>, %f: f32, %pos: index) 
+    -> (tensor<?xf32>, index)
+{
+  %c0 = arith.constant 0 : index
+  // CHECK-NOT: memref.alloc
+  // CHECK-NOT: memref.copy
+  //     CHECK: memref.store %{{.*}}, %[[t]]
+  %0 = tensor.insert %f into %t[%pos] : tensor<?xf32>
+  //     CHECK: memref.dim %[[t]]
+  %1 = tensor.dim %t, %c0 : tensor<?xf32>
+  return %0, %1 : tensor<?xf32>, index
+}