init Inference top APIs (#10549)

Author: Superjomn

contrib/inference/README.md

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+# Embed Paddle Inference in Your Application
+
+Paddle inference offers the APIs in `C` and `C++` languages.
+
+One can easily deploy a model trained by Paddle following the steps as below:
+
+1. Optimize the native model;
+2. Write some codes for deployment.
+
+
+Let's explain the steps in detail.
+
+## Optimize the native Fluid Model
+
+The native model that get from the training phase needs to be optimized for that.
+
+- Clean the noise such as the cost operators that do not need inference;
+- Prune unnecessary computation fork that has nothing to do with the output;
+- Remove extraneous variables;
+- Memory reuse for native Fluid executor;
+- Translate the model storage format to some third-party engine's, so that the inference API can utilize the engine for acceleration;
+
+We have an official tool to do the optimization, call `paddle_inference_optimize --help` for more information.
+
+## Write some codes
+
+Read `paddle_inference_api.h` for more information.

contrib/inference/paddle_inference_api.h

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+/* Copyright (c) 2018 PaddlePaddle Authors. All Rights Reserved.
+
+   Licensed 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. */
+
+#pragma once
+
+#include <string>
+#include <vector>
+
+namespace paddle {
+
+class Predictor {
+public:
+  struct Attr;
+  Predictor() = default;
+
+  // Build the network before inference.
+  bool Init(const Attr& attr);
+
+  // Predict an record.
+  // Arguments:
+  //   inputs: the name of the input variables.
+  //   outputs: the name of the output varaibles.
+  //   input_shapes: the shape of the input variables.
+  //   output_shapes: the shape of the output variables.
+  //   input_data: the data of the input variables.
+  //   output_data: the data of the output variables.
+  bool Run(const std::vector<std::string>& inputs,
+           const std::vector<std::string>& outputs,
+           const std::vector<std::vector<int>>& input_shapes,
+           const std::vector<std::vector<int>>& output_shapes,
+           const std::vector<std::vector<float>>& input_data,
+           std::vector<std::vector<float>>* output_data);
+
+  // Clone a predictor that share the model weights.
+  Predictor* Clone();
+
+  // Destroy the Predictor.
+  ~Predictor();
+
+  struct Attr {
+    enum class EngineKind;
+
+    std::string model_dir;      // path to the model directory.
+    bool enable_engine{false};  // Enable to execute (part of) the model on
+                                // third-party engines.
+    EngineKind engine_kind{Attr::EngineKind::kNone};
+
+    enum class EngineKind {
+      kNone = -1,          // Use the native Fluid facility.
+      kAnakin,             // Use Anakin for inference.
+      kTensorRT,           // Use TensorRT for inference.
+      kAutoMixedAnakin,    // Automatically mix Fluid with Anakin.
+      kAutoMixedTensorRT,  // Automatically mix Fluid with TensorRT.
+    };
+  };
+};
+
+}  // namespace paddle