comaniac commented on a change in pull request #8069:
URL: https://github.com/apache/tvm/pull/8069#discussion_r652216408



##########
File path: src/relay/transforms/to_mixed_precision.cc
##########
@@ -0,0 +1,420 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ *
+ * \file to_mixed_precision.cc
+ * \brief Automatic mixed floating point precision for relay graphs. i.e. turn 
a graph into fp16.
+ *
+ */
+
+#include <tvm/ir/attrs.h>
+#include <tvm/relay/expr_functor.h>
+#include <tvm/relay/transform.h>
+#include <tvm/runtime/object.h>
+
+#include <utility>
+
+#include "pattern_utils.h"
+
+namespace tvm {
+namespace relay {
+
+// A callable which hashes std::pair
+struct pair_hash {
+  template <class T1, class T2>
+  std::size_t operator()(const std::pair<T1, T2>& pair) const {
+    auto h1 = std::hash<T1>()(pair.first);
+    auto h2 = std::hash<T2>()(pair.second);
+
+    // Use boost's combine_hash strategy
+    return h1 ^ (h1 + 0x9e3779b9 + (h2 << 6) + (h2 >> 2));
+  }
+};
+
+// MIXED_PRECISION_ALWAYS ops should always be done in lower precision due to 
the speed and memory
+// savings. MIXED_PRECISION_FOLLOW ops can be done in lower precision but 
don't have speedups to
+// justify a cast. MIXED_PRECISION_NEVER colored ops should not be done in 
lower precision due to
+// numerical reasons.
+enum MixedTypeConversionCategory : int {
+  MIXED_PRECISION_ALWAYS = 0,
+  MIXED_PRECISION_FOLLOW = 1,
+  MIXED_PRECISION_NEVER = 2
+};
+
+// A map of a parent node and a wanted dtype to existing nodes casted to the 
wanted dtype
+using CachedCastNodes = std::unordered_map<std::pair<const ExprNode*, 
DataType>, Expr, pair_hash>;
+
+// Return array is of type : [MixedTypeConversionCategory (int), String, 
String]
+// The fields are          : [ConversionCategory, accumulation_datatype, 
output_datatype]
+// Call is a call node, DataType is the mixed precision type
+using FTVMMixedPrecisionConversionType = 
runtime::TypedPackedFunc<Array<ObjectRef>(
+    const Call& call_node, const std::string& target_dtype_str)>;
+
+class MixedPrecisionPass : public MixedModeMutator {
+ private:
+  CachedCastNodes cast_nodes_cache_;
+
+  /*! \brief The target datatype we want to convert to e.g. FP16 */
+  const DataType mixed_precision_type;

Review comment:
       Please check through all changes you've made.
   ```suggestion
     const DataType mixed_precision_type_;
   ```

##########
File path: src/relay/transforms/to_mixed_precision.cc
##########
@@ -0,0 +1,420 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ *
+ * \file to_mixed_precision.cc
+ * \brief Automatic mixed floating point precision for relay graphs. i.e. turn 
a graph into fp16.
+ *
+ */
+
+#include <tvm/ir/attrs.h>
+#include <tvm/relay/expr_functor.h>
+#include <tvm/relay/transform.h>
+#include <tvm/runtime/object.h>
+
+#include <utility>
+
+#include "pattern_utils.h"
+
+namespace tvm {
+namespace relay {
+
+// A callable which hashes std::pair
+struct pair_hash {
+  template <class T1, class T2>
+  std::size_t operator()(const std::pair<T1, T2>& pair) const {
+    auto h1 = std::hash<T1>()(pair.first);
+    auto h2 = std::hash<T2>()(pair.second);
+
+    // Use boost's combine_hash strategy
+    return h1 ^ (h1 + 0x9e3779b9 + (h2 << 6) + (h2 >> 2));
+  }
+};
+
+// MIXED_PRECISION_ALWAYS ops should always be done in lower precision due to 
the speed and memory
+// savings. MIXED_PRECISION_FOLLOW ops can be done in lower precision but 
don't have speedups to
+// justify a cast. MIXED_PRECISION_NEVER colored ops should not be done in 
lower precision due to
+// numerical reasons.
+enum MixedTypeConversionCategory : int {
+  MIXED_PRECISION_ALWAYS = 0,
+  MIXED_PRECISION_FOLLOW = 1,
+  MIXED_PRECISION_NEVER = 2
+};
+
+// A map of a parent node and a wanted dtype to existing nodes casted to the 
wanted dtype
+using CachedCastNodes = std::unordered_map<std::pair<const ExprNode*, 
DataType>, Expr, pair_hash>;
+
+// Return array is of type : [MixedTypeConversionCategory (int), String, 
String]
+// The fields are          : [ConversionCategory, accumulation_datatype, 
output_datatype]
+// Call is a call node, DataType is the mixed precision type
+using FTVMMixedPrecisionConversionType = 
runtime::TypedPackedFunc<Array<ObjectRef>(
+    const Call& call_node, const std::string& target_dtype_str)>;
+
+class MixedPrecisionPass : public MixedModeMutator {
+ private:
+  CachedCastNodes cast_nodes_cache_;

Review comment:
       docstring?

##########
File path: src/relay/transforms/to_mixed_precision.cc
##########
@@ -0,0 +1,420 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ *
+ * \file to_mixed_precision.cc
+ * \brief Automatic mixed floating point precision for relay graphs. i.e. turn 
a graph into fp16.
+ *
+ */
+
+#include <tvm/ir/attrs.h>
+#include <tvm/relay/expr_functor.h>
+#include <tvm/relay/transform.h>
+#include <tvm/runtime/object.h>
+
+#include <utility>
+
+#include "pattern_utils.h"
+
+namespace tvm {
+namespace relay {
+
+// A callable which hashes std::pair
+struct pair_hash {
+  template <class T1, class T2>
+  std::size_t operator()(const std::pair<T1, T2>& pair) const {
+    auto h1 = std::hash<T1>()(pair.first);
+    auto h2 = std::hash<T2>()(pair.second);
+
+    // Use boost's combine_hash strategy
+    return h1 ^ (h1 + 0x9e3779b9 + (h2 << 6) + (h2 >> 2));
+  }
+};
+
+// MIXED_PRECISION_ALWAYS ops should always be done in lower precision due to 
the speed and memory
+// savings. MIXED_PRECISION_FOLLOW ops can be done in lower precision but 
don't have speedups to
+// justify a cast. MIXED_PRECISION_NEVER colored ops should not be done in 
lower precision due to
+// numerical reasons.
+enum MixedTypeConversionCategory : int {
+  MIXED_PRECISION_ALWAYS = 0,
+  MIXED_PRECISION_FOLLOW = 1,
+  MIXED_PRECISION_NEVER = 2
+};
+
+// A map of a parent node and a wanted dtype to existing nodes casted to the 
wanted dtype
+using CachedCastNodes = std::unordered_map<std::pair<const ExprNode*, 
DataType>, Expr, pair_hash>;
+
+// Return array is of type : [MixedTypeConversionCategory (int), String, 
String]
+// The fields are          : [ConversionCategory, accumulation_datatype, 
output_datatype]
+// Call is a call node, DataType is the mixed precision type
+using FTVMMixedPrecisionConversionType = 
runtime::TypedPackedFunc<Array<ObjectRef>(
+    const Call& call_node, const std::string& target_dtype_str)>;
+
+class MixedPrecisionPass : public MixedModeMutator {
+ private:
+  CachedCastNodes cast_nodes_cache_;
+
+  /*! \brief The target datatype we want to convert to e.g. FP16 */
+  const DataType mixed_precision_type;
+
+  // Map of Ops with no associated FTVMMixedPrecisionConversionType to the 
times they were
+  // encountered. Used for emitting warnings on missing ops in the pass.
+  std::unordered_map<std::string, int> missing_ops;
+
+  Attrs GetNewAttrs(const CallNode* call, const DataType& accumulation_dtype) 
const {
+    /* If the accumulation dtype is in the attributes make a copy and mutate 
the field. */
+    Attrs cur_attrs = call->attrs;
+    if (cur_attrs.get() != nullptr) {
+      // TODO(AndrewZhaoLuo): Figure out a better way to do this
+      // modify output_dtype attributes (accumulation dtypes for ops)
+      if (auto attrs = cur_attrs.as<Conv1DAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<Conv1DTransposeAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<Conv2DAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<Conv2DTransposeAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<Conv2DWinogradAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = 
cur_attrs.as<Conv2DWinogradNNPACKWeightTransformAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<DeformableConv2DAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<Conv3DAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<Conv3DTransposeAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<Conv3DWinogradAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<DenseAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      } else if (auto attrs = cur_attrs.as<BatchMatmulAttrs>()) {
+        return ModifyAttrsOutputDType(attrs, accumulation_dtype);
+      }
+
+      // modify dtype attributes (creating new tensors of type dtype)
+      if (auto attrs = cur_attrs.as<InitOpAttrs>()) {
+        return ModifyAttrsDType(attrs, accumulation_dtype);
+      }
+    }
+
+    return cur_attrs;
+  }
+
+  template <typename T>
+  Attrs ModifyAttrsOutputDType(const T* attrs, const DataType& 
accumulation_dtype) const {
+    /*
+     Helper template to modify relevant attributes with out_dtype type.
+     These represent accumulation dtypes for some operations e.g.
+     conv2d might take in fp16 and give a fp32 result.
+     Attrs is const because we get it as a const.
+     */
+    DataType cur_type = (attrs->out_dtype);
+    ObjectPtr<T> new_attrs = make_object<T>(*attrs);
+    if (cur_type.is_float() || cur_type.is_void()) new_attrs->out_dtype = 
accumulation_dtype;
+    return Attrs(new_attrs);
+  }
+
+  template <typename T>
+  Attrs ModifyAttrsDType(const T* attrs, const DataType& accumulation_dtype) 
const {
+    /*
+     Helper template to modify relevant attributes with dtype type.
+     This determines the output dtype for some ops. For example
+     zeros creates a tensor of zeros of the specified dtype.
+     Attrs is const because we get it as a const.
+    */
+    DataType cur_type = (attrs->dtype);
+    ObjectPtr<T> new_attrs = make_object<T>(*attrs);
+    if (cur_type.is_float() || cur_type.is_void()) new_attrs->dtype = 
accumulation_dtype;
+    return Attrs(new_attrs);
+  }
+
+  Type GetType(const Expr& expr) const {
+    auto mod = IRModule::FromExpr(expr);
+    mod = transform::InferType()(mod);
+
+    if (expr.as<FunctionNode>()) {
+      return mod->Lookup("main")->checked_type();
+    } else {
+      return mod->Lookup("main").as<FunctionNode>()->body->checked_type();
+    }
+  }
+
+  bool IsMixedPrecisionType(const Type& t, bool ignore_non_float = false) 
const {
+    /* Returns whether t is a type with only target mixed precision type 
elements.
+       If ignore_non_float, then ignore non-floating types.
+     */
+    if (const TensorTypeNode* tensor_type = t.as<TensorTypeNode>()) {
+      return (!ignore_non_float || (tensor_type->dtype).is_float()) &&
+             tensor_type->dtype == mixed_precision_type;
+    } else if (const TupleTypeNode* tuple_type = t.as<TupleTypeNode>()) {
+      for (Type t : tuple_type->fields) {
+        if (!IsMixedPrecisionType(t, ignore_non_float)) return false;
+      }
+      return true;
+    } else {
+      LOG(FATAL) << "Unsupported type " << t << " we don't know how to handle";
+      return false;
+    }
+  }
+
+  Expr CachedCast(const Expr& expr, const DataType& expr_dtype, const 
DataType& wanted_dtype) {
+    /* Cast tensor to the wanted datatype, returning a cached version if it's 
already been done. */
+
+    // If this is not a floating point type, do not cast. E.g. it might be an 
integer
+    if (!expr_dtype.is_float()) {
+      return expr;
+    }
+
+    if (expr_dtype == wanted_dtype) {
+      return expr;
+    }
+
+    const ExprNode* expr_node = expr.as<ExprNode>();
+    CHECK(expr_node) << "Non-expression node found in cast: " << expr;
+
+    // Use cached result if possible.
+    auto search = cast_nodes_cache_.find({expr_node, wanted_dtype});
+    if (search != cast_nodes_cache_.end()) {
+      return search->second;
+    }
+
+    Expr result = Cast(expr, wanted_dtype);
+    cast_nodes_cache_[{expr_node, wanted_dtype}] = result;
+
+    // Reverse the cache result, e.g. if we want to reverse the cast simply 
point to original node
+    const ExprNode* new_expr_node = result.as<ExprNode>();
+    cast_nodes_cache_[{new_expr_node, expr_dtype}] = expr;
+    return result;
+  }
+
+  Expr CastArg(const Expr& expr, const Type& expr_type, const DataType& 
wanted_dtype) {
+    /* Helper for casting arguments to call_nodes handling all relevant cases. 
*/
+    if (const TensorTypeNode* tensor_type = expr_type.as<TensorTypeNode>()) {
+      return CachedCast(expr, tensor_type->dtype, wanted_dtype);
+    } else if (const TupleTypeNode* tuple_type = 
expr_type.as<TupleTypeNode>()) {
+      Array<Expr> new_expr;
+      bool all_same = true;
+      for (size_t i = 0; i < (tuple_type->fields).size(); i++) {
+        Expr tuple_element = GetField(expr, i);
+        Type tuple_element_dtype = (tuple_type->fields)[i];
+        Expr casted_element = CastArg(tuple_element, tuple_element_dtype, 
wanted_dtype);
+        new_expr.push_back(casted_element);
+        all_same &= casted_element.same_as(tuple_element);
+      }
+      return all_same ? expr : Tuple(new_expr);
+    }
+    CHECK(0) << "Unsupported type " << expr_type << " we don't know how to 
cast for arguments!";
+    return expr;
+  }
+
+  std::pair<Array<Expr>, Array<Type>> CastAllArgs(const Array<Expr>& cur_args,
+                                                  const Array<Type>& 
cur_arg_types,
+                                                  const DataType& 
wanted_dtype) {
+    Array<Expr> new_args;
+    Array<Type> new_arg_types;
+    for (size_t i = 0; i < cur_args.size(); i++) {
+      Expr cur_arg = cur_args[i];
+      Type cur_arg_type = cur_arg_types[i];
+      Expr new_arg = CastArg(cur_arg, cur_arg_type, wanted_dtype);
+      Type new_arg_type = GetType(new_arg);
+      new_args.push_back(new_arg);
+      new_arg_types.push_back(new_arg_type);
+    }
+    return {new_args, new_arg_types};
+  }
+
+ public:
+  using MixedModeMutator::VisitExpr_;
+
+  explicit MixedPrecisionPass(DataType mixed_precision_type = 
DataType::Float(16))
+      : MixedModeMutator(), mixed_precision_type(mixed_precision_type) {
+    if (!mixed_precision_type.is_float() && 
!mixed_precision_type.is_bfloat16()) {
+      LOG(FATAL) << "Only support IEEE floating point mixed precision types 
and bfloat16, but got "
+                 << mixed_precision_type;
+    }
+  }
+
+  Expr Rewrite_(const CallNode* pre_call_node, const Expr& post) final {
+    const CallNode* post_call_node = post.as<CallNode>();
+    CHECK(post_call_node) << "Expected a CallNode, but got " << post;
+
+    Expr cur_op = post_call_node->op;
+
+    // Get info on the operation being called:
+    // conversion category (int), accumulation dtype (str), output dtype (str)
+    MixedTypeConversionCategory initial_category;
+    DataType accumulation_dtype, output_dtype;
+    if (cur_op.as<FunctionNode>()) {
+      // Avoid messing with functions to avoid changing signature
+      initial_category = MIXED_PRECISION_NEVER;
+      accumulation_dtype = DataType::Float(32);
+      output_dtype = DataType::Float(32);
+    } else if (cur_op.as<OpNode>()) {
+      static auto attr_map =
+          
Op::GetAttrMap<FTVMMixedPrecisionConversionType>("FTVMMixedPrecisionConversionType");
+      Op op = Downcast<Op>(cur_op);
+      if (attr_map.count(op)) {
+        // Calculate the conversion category and dtypes from registered 
attribute.
+        FTVMMixedPrecisionConversionType func = attr_map[op];
+        Array<ObjectRef> op_descriptor =
+            func(GetRef<Call>(pre_call_node), 
DLDataType2String(mixed_precision_type));
+        ICHECK(op_descriptor.size() == 3)
+            << "got the wrong number of returned arguments (expected 3 got " 
<< op_descriptor.size()
+            << ") from FTVMMixedPrecisionConversionType for " << AsText(op, 
false);
+
+        int64_t op_conversion_type = 
Downcast<Integer>(op_descriptor[0])->value;
+        initial_category = 
static_cast<MixedTypeConversionCategory>(op_conversion_type);
+        accumulation_dtype = 
DataType(String2DLDataType(Downcast<String>(op_descriptor[1])));
+        output_dtype = 
DataType(String2DLDataType(Downcast<String>(op_descriptor[2])));
+      } else {
+        missing_ops[op->name] += 1;
+
+        // If not registered, by default assume is a generic FOLLOW operation.
+        initial_category = MIXED_PRECISION_FOLLOW;
+        accumulation_dtype = mixed_precision_type;
+        output_dtype = mixed_precision_type;
+      }
+    } else {
+      LOG(FATAL) << "Unsupported op type in CallNode: " << pre_call_node->op;
+    }
+
+    // First check if all the new mutated args are in lower precision form
+    Array<Type> cur_arg_types;
+    bool all_args_mixed_type_compatible = true;
+    for (Expr arg : post_call_node->args) {
+      Type cur_arg_type = GetType(arg);
+      cur_arg_types.push_back(cur_arg_type);
+
+      if (initial_category == MIXED_PRECISION_FOLLOW && 
all_args_mixed_type_compatible) {
+        // We can cast Vars and Constants to the right types so don't care 
about the types.
+        bool is_mixed_type_compatible = IsMixedPrecisionType(cur_arg_type, 
true) ||
+                                        arg->IsInstance<VarNode>() ||
+                                        arg->IsInstance<ConstantNode>();
+        all_args_mixed_type_compatible &= is_mixed_type_compatible;
+      }
+    }
+
+    // Determine the final category we want for conversion
+    MixedTypeConversionCategory final_category = initial_category;
+    if (initial_category == MIXED_PRECISION_FOLLOW) {
+      final_category =
+          all_args_mixed_type_compatible ? MIXED_PRECISION_ALWAYS : 
MIXED_PRECISION_NEVER;
+    }
+
+    // Create the new arguments to the call.
+    DataType wanted_arg_dtypes =
+        final_category == MIXED_PRECISION_ALWAYS ? mixed_precision_type : 
DataType::Float(32);
+    auto call_args_and_types = CastAllArgs(post_call_node->args, 
cur_arg_types, wanted_arg_dtypes);
+    Array<Expr> new_args = call_args_and_types.first;
+    Array<Type> new_arg_types;
+
+    if (pre_call_node->op.as<FunctionNode>()) {
+      // Function Nodes don't store type info in the Call, it should be a []
+      new_arg_types = pre_call_node->type_args;
+    } else {
+      new_arg_types = call_args_and_types.second;
+    }
+
+    // Finally create the new attributes.
+    if (final_category == MIXED_PRECISION_ALWAYS) {
+      Attrs new_attrs = GetNewAttrs(pre_call_node, accumulation_dtype);
+      Expr output = Call(cur_op, new_args, new_attrs, new_arg_types, 
pre_call_node->span);
+      if (accumulation_dtype != output_dtype) {
+        output = CastArg(output, GetType(output), output_dtype);
+      }
+      return output;
+    }
+
+    return Call(cur_op, new_args, pre_call_node->attrs, new_arg_types, 
pre_call_node->span);
+  }
+
+  Expr VisitExpr_(const FunctionNode* func) final {
+    // Erase the ret_type annotation and let the normal pass recalculate
+    const_cast<FunctionNode*>(func)->ret_type = Type(nullptr);
+    return ExprMutator::VisitExpr_(func);
+  }
+
+  Expr VisitExpr_(const LetNode* op) final {
+    // First convert as much of the bound computation to lower precision as 
possible
+    Expr value = this->Mutate(op->value);
+
+    // Then rewrite the var type and associated expression
+    Var var = Downcast<Var>(this->Mutate(op->var));
+    VarNode* mutable_var = const_cast<VarNode*>((op->var).as<VarNode>());
+    mutable_var->type_annotation = GetType(value);
+    mutable_var->checked_type_ = mutable_var->type_annotation;
+
+    // Mutate body last as it may depend on previous results
+    Expr body = this->Mutate(op->body);
+    return Let(var, value, body, op->span);
+  }
+
+  // To access map of ops not registered for error reporting
+  friend Expr ToMixedPrecision(const Expr& expr, const DataType& 
mixed_precision_type,
+                               int missing_op_mode);
+};
+
+Expr ToMixedPrecision(const Expr& expr, const DataType& mixed_precision_type, 
int missing_op_mode) {
+  /*
+  missing_op_mode:
+
+  0: Does not allow any missing ops. Will throw errors and terminate the pass 
when encountering any.
+  1: Allow missing ops but throw warnings.
+  2: Allow missing ops and silently ignore them.
+  */
+  ICHECK(missing_op_mode >= 0 && missing_op_mode <= 2)
+      << " missing_op_mode must be either 0, 1, or 2 got " << missing_op_mode;
+
+  MixedPrecisionPass converter = MixedPrecisionPass(mixed_precision_type);
+  auto result = converter.Mutate(expr);
+
+  for (auto it = converter.missing_ops.begin();
+       missing_op_mode != 2 && it != converter.missing_ops.end(); it++) {
+    std::string op_name = it->first;
+    int appear_count = it->second;
+
+    LOG(WARNING) << "Op \"" << op_name << "\" not registered "
+                 << "FTVMMixedPrecisionConversionType appears " << 
appear_count << " in graph.";
+  }
+
+  if (converter.missing_ops.size() != 0 && missing_op_mode == 0) {
+    CHECK(0) << "Missing ops were found, please fix!";

Review comment:
       I think this is not supposed to be fixed by end-users. We should direct 
them to the discuss forum to post what is missing, or provide the tutorial link 
of AMP pass in the future to help them fix it. cc @areusch 
   ```suggestion
       CHECK(0) << "Missing ops were found";
   ```

##########
File path: src/relay/transforms/to_mixed_precision.cc
##########
@@ -0,0 +1,420 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/*!
+ *
+ * \file to_mixed_precision.cc
+ * \brief Automatic mixed floating point precision for relay graphs. i.e. turn 
a graph into fp16.
+ *
+ */
+
+#include <tvm/ir/attrs.h>
+#include <tvm/relay/expr_functor.h>
+#include <tvm/relay/transform.h>
+#include <tvm/runtime/object.h>
+
+#include <utility>
+
+#include "pattern_utils.h"
+
+namespace tvm {
+namespace relay {
+
+// A callable which hashes std::pair
+struct pair_hash {
+  template <class T1, class T2>
+  std::size_t operator()(const std::pair<T1, T2>& pair) const {
+    auto h1 = std::hash<T1>()(pair.first);
+    auto h2 = std::hash<T2>()(pair.second);
+
+    // Use boost's combine_hash strategy
+    return h1 ^ (h1 + 0x9e3779b9 + (h2 << 6) + (h2 >> 2));
+  }
+};
+
+// MIXED_PRECISION_ALWAYS ops should always be done in lower precision due to 
the speed and memory
+// savings. MIXED_PRECISION_FOLLOW ops can be done in lower precision but 
don't have speedups to
+// justify a cast. MIXED_PRECISION_NEVER colored ops should not be done in 
lower precision due to
+// numerical reasons.
+enum MixedTypeConversionCategory : int {
+  MIXED_PRECISION_ALWAYS = 0,
+  MIXED_PRECISION_FOLLOW = 1,
+  MIXED_PRECISION_NEVER = 2
+};
+
+// A map of a parent node and a wanted dtype to existing nodes casted to the 
wanted dtype
+using CachedCastNodes = std::unordered_map<std::pair<const ExprNode*, 
DataType>, Expr, pair_hash>;
+
+// Return array is of type : [MixedTypeConversionCategory (int), String, 
String]
+// The fields are          : [ConversionCategory, accumulation_datatype, 
output_datatype]
+// Call is a call node, DataType is the mixed precision type
+using FTVMMixedPrecisionConversionType = 
runtime::TypedPackedFunc<Array<ObjectRef>(
+    const Call& call_node, const std::string& target_dtype_str)>;
+
+class MixedPrecisionPass : public MixedModeMutator {
+ private:
+  CachedCastNodes cast_nodes_cache_;
+
+  /*! \brief The target datatype we want to convert to e.g. FP16 */
+  const DataType mixed_precision_type;
+
+  // Map of Ops with no associated FTVMMixedPrecisionConversionType to the 
times they were
+  // encountered. Used for emitting warnings on missing ops in the pass.
+  std::unordered_map<std::string, int> missing_ops;

Review comment:
       ```suggestion
     /*! \brief Map of Ops with no associated FTVMMixedPrecisionConversionType 
to the times they were
      * encountered. Used for emitting warnings on missing ops in the pass.
      */
     std::unordered_map<std::string, int> missing_ops_;
   ```




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