[Relay] Convert Layout Pass.

include/tvm/relay/op_attr_types.h

@@ -29,6 +29,7 @@
 #include <tvm/build_module.h>
 #include <tvm/relay/type.h>
 #include <tvm/relay/expr.h>
+#include <string>
 
 namespace tvm {
 namespace relay {
@@ -132,6 +133,22 @@ using FTVMAlterOpLayout = runtime::TypedPackedFunc<
        const Array<Expr>& args,
        const Array<Tensor>& tinfos)>;
 
+/*!
+ * \brief Convert the layout of operators or replace the
+ *  operator with other expressions. This function will be invoked
+ *  in ConvertLayout pass.
+ * \param attrs The attribute of the original node.
+ * \param inputs The input symbols of the original node.
+ * \param tinfos An array of placeholders, use for getting the inferred shape
+ *               and dtype of the inputs.
+ * \param desired_layout The desired layout.
+ * \return new_expr The modified expression.
+ */
+using FTVMConvertOpLayout = runtime::TypedPackedFunc<
+  Expr(const Attrs& attrs,
+       const Array<Expr>& args,
+       const Array<Tensor>& tinfos,
+       const std::string& desired_layout)>;
 /*!
  * \brief Legalizes an expression with another expression. This function will be
  *  invoked in Legalize pass. It is a target-dependent pass.

include/tvm/relay/transform.h

@@ -532,6 +532,26 @@ TVM_DLL Pass CanonicalizeOps();
  */
 TVM_DLL Pass AlterOpLayout();
 
+/*!
+ * \brief Given a dest layout, this pass transforms the expr such that most of the ops input data
+ * layout is changed to the dest layout. In ideal situation, there are only 2 layout transforms, one
+ * at the start and one at the end.
+ *
+ * This pass is not a part of relay.build and is expected to be called between framework-relay
+ * parser and relay.build call. This is very helpful for hardware backends that support/prefer only
+ * type of data layout.
+ *
+ * RFC - https://discuss.tvm.ai/t/layout-conversion-pass/4009
+ *
+ * This pass uses most of the AlterOpLayout and InferCorrectLayout infrastructure. We can define new
+ * layouts for conv2d ops for now. Most of the other operators try to adapt to their input layout
+ * using the InferCorrectLayout infrastructure.
+ *
+ * \param desired_layout The desired layout.
+ * \return The pass.
+ */
+TVM_DLL Pass ConvertLayout(const std::string& desired_layout);
+
 /*!
  * \brief Legalizes an expr with another expression.
  * \param legalize_map_attr_name The Op's attr name which corresponds to the legalize rule function.

python/tvm/relay/op/nn/_nn.py

@@ -251,6 +251,47 @@ def legalize_conv2d(attrs, inputs, types):
     """
     return topi.nn.conv2d_legalize(attrs, inputs, types)
 
+
+@reg.register_convert_op_layout("nn.conv2d")
+def convert_conv2d(attrs, inputs, tinfos, desired_layout):
+    """Convert Layout pass registration for conv2d op.
+
+    Parameters
+    ----------
+    attrs : tvm.attrs.Attrs
+        Attributes of current convolution
+    inputs : list of tvm.relay.Expr
+        The args of the Relay expr to be legalized
+    tinfos : list of types
+        List of input and output types
+    desired_layout : str
+        The desired layout
+
+    Returns
+    -------
+    result : tvm.relay.Expr
+        The transformed expr
+    """
+
+    from tvm import relay
+    data_layout = attrs['data_layout']
+    kernel_layout = attrs['kernel_layout']
+    data, weight = inputs
+    assert desired_layout == 'NCHW', \
+            "Currently only transformation to NCHW layout is supported."
+    if desired_layout == 'NCHW':
+        new_attrs = dict(attrs)
+        new_attrs['data_layout'] = desired_layout
+        new_attrs['kernel_layout'] = 'OIHW'
+
+        if data_layout == 'NHWC' and kernel_layout == 'HWIO':
+            # Convert (NHWC, HWIO) to (NCHW, OIHW)
+            return relay.nn.conv2d(data, weight, **new_attrs)
+        if data_layout == 'NHWC' and kernel_layout == 'HWOI':
+            # Convert (NHWC, HWOI) to (NCHW, OIHW). Depthwise conv2d.
+            return relay.nn.conv2d(data, weight, **new_attrs)
+    return None
+
 reg.register_pattern("nn.conv2d", OpPattern.OUT_ELEMWISE_FUSABLE)
 
 

python/tvm/relay/op/op.py

@@ -196,6 +196,23 @@ def register_alter_op_layout(op_name, alter_layout=None, level=10):
     return register(op_name, "FTVMAlterOpLayout", alter_layout, level)
 
 
+def register_convert_op_layout(op_name, convert_layout=None, level=10):
+    """Register convert op layout function for an op
+
+    Parameters
+    ----------
+    op_name : str
+        The name of the operator
+
+    convert_layout: function (attrs: Attrs, inputs: List[Expr]) -> new_expr: Expr
+        The function for changing the layout or replacing the operator
+
+    level : int
+        The priority level
+    """
+    return register(op_name, "FTVMConvertOpLayout", convert_layout, level)
+
+
 def register_legalize(op_name, legal_op=None, level=10):
     """Register legal transformation function for an op
 

python/tvm/relay/transform.py

@@ -460,6 +460,34 @@ def AlterOpLayout():
     return _transform.AlterOpLayout()
 
 
+def ConvertLayout(desired_layout):
+    """ Given a dest layout, this pass transforms the expr such that most of the ops input data
+    layout is changed to the dest layout. In ideal situation, there are only 2 layout transforms,
+    one at the start and one at the end.
+
+    This pass is not a part of relay.build and is expected to be called between framework-relay
+    parser and relay.build call. This is very helpful for hardware backends that support/prefer only
+    type of data layout.
+
+    RFC - https://discuss.tvm.ai/t/layout-conversion-pass/4009
+
+    This pass uses most of the AlterOpLayout and InferCorrectLayout infrastructure. We can define
+    new layouts for conv2d ops for now. Most of the other operators try to adapt to their input
+    layout using the InferCorrectLayout infrastructure.
+
+    Parameters
+    ----------
+    desired_layout : str
+      The desired layout for the transformed expr.
+
+    Returns
+    -------
+    pass: FunctionPass
+      The pass.
+    """
+    return _transform.ConvertLayout(desired_layout)
+
+
 def Legalize(legalize_map_attr_name="FTVMLegalize"):
     """Legalizes an expression with another expression.
     This pass can be used to replace an expr with another expr for target

src/relay/op/annotation/annotation.cc

@@ -30,7 +30,7 @@
 #include <tvm/relay/op_attr_types.h>
 #include <topi/elemwise.h>
 
-#include "../../pass/alter_op_layout.h"
+#include "../../pass/infer_layout_util.h"
 #include "../type_relations.h"
 
 namespace tvm {

src/relay/op/device_copy.cc

@@ -33,7 +33,7 @@
 #include <tvm/relay/op_attr_types.h>
 
 #include "type_relations.h"
-#include "../pass/alter_op_layout.h"
+#include "../pass/infer_layout_util.h"
 
 namespace tvm {
 namespace relay {

src/relay/op/memory/memory.cc

@@ -29,7 +29,7 @@
 #include <tvm/relay/attrs/memory.h>
 
 #include "../op_common.h"
-#include "../../pass/alter_op_layout.h"
+#include "../../pass/infer_layout_util.h"
 #include "../type_relations.h"
 
 namespace tvm {

src/relay/op/nn/bitserial.cc

@@ -26,7 +26,7 @@
 #include <tvm/relay/attrs/bitserial.h>
 #include <tvm/relay/op.h>
 
-#include "../../pass/alter_op_layout.h"
+#include "../../pass/infer_layout_util.h"
 
 namespace tvm {
 namespace relay {

src/relay/op/nn/convolution.cc

@@ -27,7 +27,7 @@
 #include <tvm/relay/attrs/nn.h>
 #include <vector>
 
-#include "../../pass/alter_op_layout.h"
+#include "../../pass/infer_layout_util.h"
 #include "../op_common.h"
 #include "convolution.h"
 

src/relay/op/nn/nn.cc

@@ -32,7 +32,7 @@
 #include <topi/nn/flatten.h>
 #include <vector>
 #include "../type_relations.h"
-#include "../../pass/alter_op_layout.h"
+#include "../../pass/infer_layout_util.h"
 #include "../op_common.h"
 #include "nn.h"
 

src/relay/op/nn/pooling.cc

@@ -27,7 +27,7 @@
 #include <tvm/relay/attrs/nn.h>
 #include <topi/nn/pooling.h>
 #include <vector>
-#include "../../pass/alter_op_layout.h"
+#include "../../pass/infer_layout_util.h"
 
 namespace tvm {
 namespace relay {

src/relay/op/nn/sparse.cc

@@ -27,7 +27,7 @@
 #include <tvm/relay/attrs/nn.h>
 #include <vector>
 
-#include "../../pass/alter_op_layout.h"
+#include "../../pass/infer_layout_util.h"
 
 namespace tvm {
 namespace relay {

src/relay/op/op_common.h

@@ -32,7 +32,7 @@
 #include <string>
 #include <unordered_map>
 #include "type_relations.h"
-#include "../pass/alter_op_layout.h"
+#include "../pass/infer_layout_util.h"
 
 namespace tvm {
 namespace relay {

src/relay/op/tensor/transform.cc

@@ -36,7 +36,7 @@
 #include <vector>
 #include "../op_common.h"
 #include "../../../arithmetic/compute_expr.h"
-#include "../../pass/alter_op_layout.h"
+#include "../../pass/infer_layout_util.h"
 #include "../../pass/pattern_util.h"
 #include "transform.h"