[mlir] add memref dialect as dependent of lower-affine pass

[ftynse]

Summary

The lower-affine pass also processes affine load and store operations
that get converted to load and store operations now available in the
memref dialect. Since it produces operations from the memref dialect,
this dialect should be registered as dependent for this pass. It is rare
but possible to have code that doesn't have memref operations in the
input and calls this pass.

mlir/include/mlir/Conversion/Passes.td

let description = [{
     -   Functions without a body are not modified.
     -   The semantics of the other functions is preserved.
     -   Individual operations other than those mentioned above are not modified
         if they do not depend on the loop iterator value or on the result of
         `affine.apply`.
   }];
   let constructor = "mlir::createLowerAffinePass()";
   let dependentDialects = [
+    "memref::MemRefDialect",
     "scf::SCFDialect",
     "StandardOpsDialect",
     "vector::VectorDialect"
   ];
 }
 
 //===----------------------------------------------------------------------===//
 // AsyncToLLVM

mlir/test/Conversion/AffineToStandard/no-memref.mlir

+// RUN: mlir-opt -lower-affine %s | FileCheck %s
+
+// Regression test checking that the memref dialect is loaded as dependency by
+// the lowering pass. We shouldn't fail trying to create memref.load here.
+
+// CHECK-LABEL: @no_memref_op
+func @no_memref_op(%arg0: memref<f32>) {
+  // CHECK: memref.load
+  affine.load %arg0[] : memref<f32>
+  return
+}