Update native_infer_en.md (#787)

doc/fluid/advanced_usage/deploy/inference/native_infer_en.md

@@ -96,7 +96,7 @@ There are two modes in term of memory management in `PaddleBuf` :
 
 In the two modes, the first is more convenient while the second strictly controls memory management to facilitate integration with `tcmalloc` and other libraries.
  
-### Upgrade performance based on contrib::AnalysisConfig (Prerelease)
+### Upgrade performance based on contrib::AnalysisConfig
 
 AnalyisConfig is at the stage of pre-release and protected by `namespace contrib` , which may be adjusted in the future.
 
@@ -106,9 +106,11 @@ The usage of `AnalysisConfig` is similiar with that of `NativeConfig` but the fo
 
 ```c++
 AnalysisConfig config;
-config.model_dir = xxx;
-config.use_gpu = false;  // GPU optimization is not supported at present
-config.specify_input_name = true; // it needs to set name of input
+config.SetModel(dirname);                // set the directory of the model
+config.EnableUseGpu(100, 0 /*gpu id*/);  // use GPU,or
+config.DisableGpu();                     // use CPU
+config.SwitchSpecifyInputNames(true);    // need to appoint the name of your input
+config.SwitchIrOptim();     // turn on the optimization switch,and a sequence of optimizations will be executed in operation                      
 ```
 
 Note that input PaddleTensor needs to be allocated. Previous examples need to be revised as follows:
@@ -147,7 +149,7 @@ For more specific examples, please refer to[LoD-Tensor Instructions](../../../us
 
 1. If the CPU type permits, it's best to use the versions with support for AVX and MKL.
 2. Reuse input and output `PaddleTensor` to avoid frequent memory allocation resulting in low performance
-3. Try to replace `NativeConfig` with `AnalysisConfig` to perform optimization for CPU inference 
+3. Try to replace `NativeConfig` with `AnalysisConfig` to perform optimization for CPU or GPU inference 
 
 ## Code Demo