[Op][Layout] Add layout_transform operator in Relax. (#403)

Adds layout_transform operator in Relax as part of Relax layout planning.

layout_transform takes an input tensor x and an attribute index_map of tir::IndexMap type. It also has an optional pad_value attribute. It transforms x as per the index_map attribute and returns the transformed tensor.

This operator for now allows layout transformations that introduce implicit padding. For example, transforming a tensor of shape (10,) using the lambda i: (i//4, i%4). The output shape will be (3, 4) with two elements padded. The optional pad_value is used to pad if specified, otherwise the compiler is free to choose any value to pad.

include/tvm/relax/attrs/manipulate.h

@@ -25,6 +25,7 @@
 #define TVM_RELAX_ATTRS_MANIPULATE_H_
 
 #include <tvm/relax/expr.h>
+#include <tvm/tir/index_map.h>
 
 namespace tvm {
 namespace relax {
@@ -52,6 +53,21 @@ struct ExpandDimsAttrs : public tvm::AttrsNode<ExpandDimsAttrs> {
   }
 };  // struct ExpandDimsAttrs
 
+/*! \brief Attributes used in layout_transform operator */
+struct LayoutTransformAttrs : public tvm::AttrsNode<LayoutTransformAttrs> {
+  tir::IndexMap index_map;
+  // pad_value is chosen to be of PrimValue type, as it represents constant TIR POD expression. This
+  // needs to be revisited in case PrimValue is evolved to represent symbolic expression in future.
+  Optional<PrimValue> pad_value;
+
+  TVM_DECLARE_ATTRS(LayoutTransformAttrs, "relax.attrs.LayoutTransformAttrs") {
+    TVM_ATTR_FIELD(index_map).describe("The layout transformation to apply.");
+    TVM_ATTR_FIELD(pad_value).describe(
+        "The specific value to be used to pad if the layout transform would result in implicit "
+        "padding. If not specified, the compiler is free to choose any value.");
+  }
+};  // struct LayoutTransformAttrs
+
 /*! \brief Attributes used in permute_dims operator */
 struct PermuteDimsAttrs : public tvm::AttrsNode<PermuteDimsAttrs> {
   Optional<Array<Integer>> axes;

python/tvm/relax/op/manipulate.py

@@ -15,13 +15,13 @@
 # specific language governing permissions and limitations
 # under the License.
 """Manipulation operators."""
-from typing import List, Optional, Tuple, Union
+from typing import List, Optional, Tuple, Union, Callable
 
 from tvm.ir.expr import PrimExpr
-from tvm.tir import IntImm
+from tvm.tir import IntImm, FloatImm, IndexMap
 
 from . import _ffi_api
-from ..expr import Expr, ShapeExpr, Tuple as RxTuple
+from ..expr import Expr, PrimValue, ShapeExpr, Tuple as RxTuple
 
 
 PrimExprLike = Union[int, PrimExpr]
@@ -110,6 +110,47 @@ def flatten(x: Expr) -> Expr:
     return _ffi_api.flatten(x)  # type: ignore
 
 
+def layout_transform(
+    x: Expr,
+    index_map: Union[Callable, IndexMap],
+    pad_value: Optional[Union[int, float, PrimValue]] = None,
+):
+    """Modifies the layout of a tensor.
+
+    Parameters
+    ----------
+    x : relax.Expr
+        The input tensor to the operator.
+
+    index_map : Union[Callable, IndexMap]
+        The transformation to apply.
+
+    pad_value : Optional[Union[int, float, PrimValue]]
+        The value used for padding if the transformation results in implicit padding.
+        If not specified, any value can be used.
+
+    Returns
+    -------
+    result : relax.Expr
+        The transformed tensor.
+    """
+    if callable(index_map):
+        index_map = IndexMap.from_func(index_map)
+    x_dtype = x.checked_type.dtype
+
+    # Explicitly convert python int/float pad_value to the x's type.  If the default behavior
+    # is applied, it would be converted to int32/float32, which may not match the x's type.
+    if pad_value is None:
+        pass
+    elif not isinstance(pad_value, PrimValue):
+        if "int" in x_dtype and isinstance(pad_value, int):
+            pad_value = IntImm(x_dtype, pad_value)
+        elif "float" in x_dtype and (isinstance(pad_value, (int, float))):
+            pad_value = FloatImm(x_dtype, float(pad_value))
+        pad_value = PrimValue(pad_value)
+    return _ffi_api.layout_transform(x, index_map, pad_value)  # type: ignore
+
+
 def permute_dims(x: Expr, axes: Optional[List[int]] = None) -> Expr:
     """Permutes the dimensions of an array.
 

python/tvm/relax/op/op_attrs.py

@@ -139,6 +139,11 @@ class BatchNormAttrs(Attrs):
     """Attributes used in batch_norm operator"""
 
 
+@tvm._ffi.register_object("relax.attrs.LayoutTransformAttrs")
+class LayoutTransformAttrs(Attrs):
+    """Attributes used in layout_transform operator"""
+
+
 @tvm._ffi.register_object("relax.attrs.LayerNormAttrs")
 class LayerNormAttrs(Attrs):
     """Attributes used in layer_norm operator"""

python/tvm/script/ir_builder/relax/ir.py

@@ -65,6 +65,7 @@
     isfinite,
     isinf,
     isnan,
+    layout_transform,
     less,
     less_equal,
     linear,
@@ -498,6 +499,7 @@ def dtype(value: Union[py_str, DataType]) -> Expr:
     "isfinite",
     "isinf",
     "isnan",
+    "layout_transform",
     "less",
     "less_equal",
     "linear",

src/relax/op/tensor/manipulate.cc

@@ -391,6 +391,79 @@ TVM_REGISTER_OP("relax.flatten")
     .add_argument("x", "Tensor", "The input tensor.")
     .set_attr<FInferStructInfo>("FInferStructInfo", InferStructInfoFlatten);
 
+/* relax.layout_transform */
+TVM_REGISTER_NODE_TYPE(LayoutTransformAttrs);
+
+Expr layout_transform(Expr x, tir::IndexMap index_map, Optional<PrimValue> pad_value) {
+  ObjectPtr<LayoutTransformAttrs> attrs = make_object<LayoutTransformAttrs>();
+  attrs->index_map = std::move(index_map);
+  attrs->pad_value = std::move(pad_value);
+
+  static const Op& op = Op::Get("relax.layout_transform");
+  return Call(op, {std::move(x)}, Attrs{attrs}, {});
+}
+
+TVM_REGISTER_GLOBAL("relax.op.layout_transform").set_body_typed(layout_transform);
+
+StructInfo InferStructInfoLayoutTransform(const Call& call, const BlockBuilder& ctx) {
+  TensorStructInfo data_sinfo = GetUnaryInputTensorStructInfo(call, ctx);
+  const auto* attrs = call->attrs.as<LayoutTransformAttrs>();
+  tir::IndexMap index_map = attrs->index_map;
+  Optional<PrimValue> optional_pad_value = attrs->pad_value;
+
+  // Check pad_value has same dtype as input.
+  if (optional_pad_value.defined()) {
+    PrimExpr padded_value = optional_pad_value.value()->value;
+    if (padded_value->dtype != data_sinfo->dtype) {
+      ctx->ReportFatal(Diagnostic::Error(call)
+                       << "layout_transform pad_value dtype (" << padded_value->dtype
+                       << ") and input dtype (" << data_sinfo->dtype << ") must be the same");
+    }
+  }
+
+  // We would like to ensure safety, and therefore placed a stronger requirement for user to
+  // use MatchCast before layout_transform if the shape of input is not known at compile time.
+  // Todo(relax-team): At this moment, enforcing MatchCast is fine. But we may need to revisit
+  // this requirement to reduce the workload of importers and better support dynamic shapes.
+  auto report_error_for_unknown_shape =
+      [&]() {
+        ctx->ReportFatal(
+            Diagnostic::Error(call)
+            << "layout_transform expects the input tensor to have known rank (expected rank = "
+            << index_map->initial_indices.size()
+            << ") and shape. For input tensors, whose shape cannot be determined at compile time, "
+               "please use MatchCast to get input with symbolic shape.");
+        return TensorStructInfo(data_sinfo->dtype, /*ndim=*/index_map->final_indices.size());
+      };
+
+  if (data_sinfo->IsUnknownNdim()) return report_error_for_unknown_shape();
+
+  // If rank is known, check that it is compatible with the index_map, i.e., #dims match.
+  if (index_map->initial_indices.size() != static_cast<size_t>(data_sinfo->ndim)) {
+    ctx->ReportFatal(Diagnostic::Error(call)
+                     << "number of dimensions in input must match the number of source dimensions "
+                        "in index map, but got "
+                     << data_sinfo->ndim << " != " << index_map->initial_indices.size());
+  }
+
+  if (!data_sinfo->shape.defined()) return report_error_for_unknown_shape();
+
+  // If input shape is known, get the ShapeStructInfo of the shape expr.
+  const auto* shape_sinfo = GetStructInfoAs<ShapeStructInfoNode>(data_sinfo->shape.value());
+
+  if (!shape_sinfo->values.defined()) return report_error_for_unknown_shape();
+
+  Array<PrimExpr> input_shape = shape_sinfo->values.value();
+  Array<PrimExpr> output_shape = index_map->MapShape(input_shape);
+  return TensorStructInfo(ShapeExpr(output_shape), data_sinfo->dtype);
+}
+
+TVM_REGISTER_OP("relax.layout_transform")
+    .set_num_inputs(1)
+    .set_attrs_type<LayoutTransformAttrs>()
+    .add_argument("x", "Tensor", "The input tensor.")
+    .set_attr<FInferStructInfo>("FInferStructInfo", InferStructInfoLayoutTransform);
+
 /* relax.permute_dims */
 TVM_REGISTER_NODE_TYPE(PermuteDimsAttrs);
 

src/relax/op/tensor/manipulate.h

@@ -59,6 +59,16 @@ Expr expand_dims(Expr x, Array<Integer> axis);
  */
 Expr flatten(Expr x);
 
+/*!
+ * \brief Transform layout of a tensor.
+ * \param x The input data to the operator.
+ * \param index_map The transformation to apply.
+ * \param pad_value The value used for padding if the transformation results in implicit padding. If
+ * not specified, any value can be used.
+ * \return The transformed result.
+ */
+Expr layout_transform(Expr x, tir::IndexMap index_map, Optional<PrimValue> pad_value);
+
 /*!
  * \brief Permutes the dimensions of an array.
  * \param x The input data to the operator.

src/relay/printer/relax_script_printer.cc

@@ -24,6 +24,7 @@
 
 #include <tvm/ir/type_functor.h>
 #include <tvm/relax/analysis.h>
+#include <tvm/relax/attrs/manipulate.h>
 #include <tvm/relax/ir_functor.h>
 #include <tvm/relax/utils.h>
 
@@ -400,6 +401,10 @@ Doc RelaxScriptPrinter::VisitExpr_(const tir::IntImmNode* op) {
   return Doc::Text(std::to_string(op->value));
 }
 
+Doc RelaxScriptPrinter::VisitExpr_(const tir::FloatImmNode* op) {
+  return Doc::Text(std::to_string(op->value));
+}
+
 #define TVM_DEFINE_RELAX_PRINTER_PRIMEXPR_BINOP(OpName, OpString) \
   Doc RelaxScriptPrinter::VisitExpr_(const OpName* op) {          \
     Doc doc;                                                      \
@@ -491,6 +496,11 @@ std::vector<Doc> RelaxScriptPrinter::PrintAttrs(const Attrs& attrs) {
     for (const auto& k : dict_attrs->dict) {
       kwargs.push_back(Doc::Text(k.first) << "=" << Print(k.second));
     }
+  } else if (const LayoutTransformAttrs* layout_attrs = attrs.as<LayoutTransformAttrs>()) {
+    kwargs.push_back(Doc::Text("index_map=") << layout_attrs->index_map->ToPythonString());
+    if (layout_attrs->pad_value.defined()) {
+      kwargs.push_back(Doc::Text("pad_value=") << Print(layout_attrs->pad_value.value()));
+    }
   } else {
     AttrPrinter attr_printer(&kwargs, this);
     const_cast<BaseAttrsNode*>(attrs.operator->())->VisitAttrs(&attr_printer);

src/relay/printer/text_printer.h

@@ -287,6 +287,7 @@ class RelaxScriptPrinter : public relax::IRFunctor<Doc(const ObjectRef&)>,
   // PrimExpr nodes allowed in Relax
   Doc VisitExpr_(const tir::VarNode* op) override;
   Doc VisitExpr_(const tir::IntImmNode* op) override;
+  Doc VisitExpr_(const tir::FloatImmNode* op) override;
   Doc VisitExpr_(const tir::AddNode* op) override;
   Doc VisitExpr_(const tir::SubNode* op) override;
   Doc VisitExpr_(const tir::MulNode* op) override;

tests/python/relax/test_op_manipulate.py

@@ -33,6 +33,9 @@ def test_op_correctness():
     assert relax.op.reshape(x, (4, 5, 3)).op == Op.get("relax.reshape")
     assert relax.op.split(x, indices_or_sections=1).op == Op.get("relax.split")
     assert relax.op.squeeze(x).op == Op.get("relax.squeeze")
+    assert relax.op.layout_transform(x, index_map=lambda a, b, c: (b, c, a)).op == Op.get(
+        "relax.layout_transform"
+    )
 
 
 def _check_inference(bb: relax.BlockBuilder, call: relax.Call, expected_sinfo: relax.StructInfo):
@@ -657,6 +660,116 @@ def test_expand_dims_infer_struct_info_wrong_input_type():
         bb.normalize(relax.op.expand_dims(x1, axis=[]))
 
 
+def test_layout_transform_infer_struct_info():
+    bb = relax.BlockBuilder()
+    x = relax.Var("x", R.Tensor((10, 20, 30), "float32"))
+
+    transpose_transform = lambda a, b, c: (a, c, b)
+    _check_inference(
+        bb,
+        relax.op.layout_transform(x, index_map=transpose_transform),
+        relax.TensorStructInfo((10, 30, 20), "float32"),
+    )
+
+    tiling_transform = lambda a, b, c: (a, b // 2, c, b % 2)
+    _check_inference(
+        bb,
+        relax.op.layout_transform(x, index_map=tiling_transform),
+        relax.TensorStructInfo((10, 10, 30, 2), "float32"),
+    )
+
+    implicit_padding_transform = lambda a, b, c: (a, c, b // 3, b % 3)
+    _check_inference(
+        bb,
+        relax.op.layout_transform(x, index_map=implicit_padding_transform, pad_value=2),
+        relax.TensorStructInfo((10, 30, 7, 3), "float32"),
+    )
+
+    flatten_transform = lambda a, b, c: (a * 600 + b * 30 + c)
+    _check_inference(
+        bb,
+        relax.op.layout_transform(x, index_map=flatten_transform),
+        relax.TensorStructInfo((6000,), "float32"),
+    )
+
+
+def test_layout_transform_infer_struct_info_mismatch_dtype():
+    bb = relax.BlockBuilder()
+    x = relax.Var("x", R.Tensor((10, 20, 30), "int32"))
+
+    transpose_transform = lambda a, b, c: (a, c, b)
+    with pytest.raises(TVMError):
+        bb.normalize(relax.op.layout_transform(x, index_map=transpose_transform, pad_value=2.2))
+
+
+def test_layout_transform_infer_struct_info_unknown_shape():
+    bb = relax.BlockBuilder()
+    tiling_transform = lambda a, b: (a, b // 2, b % 2)
+
+    x_unknown_shape = relax.Var("x", R.Tensor("float32", ndim=2))
+    with pytest.raises(TVMError):
+        bb.normalize(relax.op.layout_transform(x_unknown_shape, index_map=tiling_transform))
+
+    x_unknown_rank_dtype = relax.Var("x", R.Tensor())
+    with pytest.raises(TVMError):
+        bb.normalize(relax.op.layout_transform(x_unknown_rank_dtype, index_map=tiling_transform))
+
+
+def test_layout_transform_infer_struct_info_symbolic_shape():
+    bb = relax.BlockBuilder()
+    a = tir.Var("a", "int64")
+    b = tir.Var("b", "int64")
+    x0 = relax.Var("x", R.Tensor((a, b), "float32"))
+
+    tiling_transform = lambda a, b: (a, b // 3, b % 3)
+    _check_inference(
+        bb,
+        relax.op.layout_transform(x0, index_map=tiling_transform),
+        relax.TensorStructInfo((a, (b - b % (-3)) // 3, 3), "float32"),
+    )
+
+
+def test_layout_transform_infer_struct_info_shape_var():
+    bb = relax.BlockBuilder()
+
+    s = relax.Var("s", relax.ShapeStructInfo((30, 20)))
+    x = relax.Var("x", relax.TensorStructInfo(s, "float32"))
+    tiling_padding_transform = lambda a, b: (a, b // 3, b % 3)
+    _check_inference(
+        bb,
+        relax.op.layout_transform(x, index_map=tiling_padding_transform),
+        relax.TensorStructInfo((30, 7, 3), "float32"),
+    )
+
+    s_unknown_shape = relax.Var("s", relax.ShapeStructInfo(ndim=2))
+    x_unknown_shape = relax.Var("x", relax.TensorStructInfo(s_unknown_shape, "float32"))
+    with pytest.raises(TVMError):
+        bb.normalize(relax.op.layout_transform(x_unknown_shape, index_map=tiling_padding_transform))
+
+    s_unknown_rank = relax.Var("s", relax.ShapeStructInfo())
+    x_unknown_rank = relax.Var("x", relax.TensorStructInfo(s_unknown_rank, "float32"))
+    with pytest.raises(TVMError):
+        bb.normalize(relax.op.layout_transform(x_unknown_rank, index_map=tiling_padding_transform))
+
+    a = tir.Var("a", "int64")
+    b = tir.Var("b", "int64")
+    s_symbolic_shape = relax.Var("s", relax.ShapeStructInfo((a, b)))
+    x_symbolic_shape = relax.Var("x", relax.TensorStructInfo(s_symbolic_shape, "float32"))
+    _check_inference(
+        bb,
+        relax.op.layout_transform(x_symbolic_shape, index_map=tiling_padding_transform),
+        relax.TensorStructInfo((a, (b - b % (-3)) // 3, 3), "float32"),
+    )
+
+
+def test_layout_transform_infer_struct_info_invalid_index_map():
+    bb = relax.BlockBuilder()
+    x = relax.Var("x", R.Tensor((10, 20, 30), "float32"))
+
+    with pytest.raises(TVMError):
+        bb.normalize(relax.op.layout_transform(x, index_map=lambda a, b: (b, a)))
+
+
 def test_squeeze_infer_struct_info():
     bb = relax.BlockBuilder()
     x0 = relax.Var("x", R.Tensor((2, 1, 3, 1, 1, 4), "float32"))