Translate the iOS build doc

doc/mobile/cross_compiling_for_ios_cn.md

@@ -18,37 +18,19 @@ PaddlePaddle为交叉编译提供了工具链配置文档[cmake/cross_compiling/
 
 - `CMAKE_SYSTEM_NAME`，CMake编译的目标平台，必须设置为`iOS`。在设置`CMAKE_SYSTEM_NAME=iOS`后，PaddlePaddle的CMake系统会自动编译所有的第三方依赖库，并且强制设置一些PaddlePaddle参数的值（`WITH_C_API=ON`、`WITH_GPU=OFF`、`WITH_AVX=OFF`、`WITH_PYTHON=OFF`、`WITH_RDMA=OFF`）。
 - `WITH_C_API`，是否编译C-API预测库，必须设置为ON。在iOS平台上只支持使用C-API来预测。
-- `WITH_SWIG_PY`，必须设置为ON。在iOS平台上不支持通过swig调用来训练或者预测。
+- `WITH_SWIG_PY`，必须设置为OFF。在iOS平台上不支持通过swig调用来训练或者预测。
 
 iOS平台可选配置参数：
 
-- `IOS_PLATFORM`，可设置为`OS/SIMULATOR`，默认值为`OS`。
+- `IOS_PLATFORM`，可设置为`OS`或者`SIMULATOR`，默认值为`OS`。
   - `OS`，构建目标为`arm`架构的iPhone或者iPad等物理设备。
   - `SIMULATOR`，构建目标为`x86`架构的模拟器平台。
 - `IOS_ARCH`，目标架构。针对不同的`IOS_PLATFORM`，可设置的目标架构如下表所示，默认编译所有架构：
 
-    <table class="docutils">
-    <colgroup>
-      <col width="35%" />
-      <col width="65%" />
-    </colgroup>
-    <thead valign="bottom">
-      <tr class="row-odd">
-      <th class="head">IOS_PLATFORM</th>
-      <th class="head">IOS_ARCH</th>
-    </tr>
-    </thead>
-    <tbody valign="top">
-      <tr class="row-even">
-      <td>OS</td>
-      <td>armv7, armv7s, arm64 </td>
-    </tr>
-    <tr class="row-odd">
-      <td>SIMULATOR</td>
-      <td>i386, x86_64 </td>
-    </tr>
-    </tbody>
-    </table>
+  | `IOS_PLATFORM` | `IOS_ARCH` |
+  |----------------|------------|
+  | `OS`           | armv7, armv7s, arm64 |
+  | `SIMULATOR`    | i386, x86_64 |
 
 - `IOS_DEPLOYMENT_TARGET`，最小的iOS部署版本，默认值为`7.0`。
 - `IOS_ENABLE_BITCODE`，是否使能[Bitcode](https://developer.apple.com/library/content/documentation/IDEs/Conceptual/AppDistributionGuide/AppThinning/AppThinning.html#//apple_ref/doc/uid/TP40012582-CH35-SW3)，可设置`ON/OFF`，默认值为`ON`。

doc/mobile/cross_compiling_for_ios_en.md

@@ -0,0 +1,132 @@
+# Build PaddlePaddle for iOS
+
+The cross-compiling of iOS requires a MacOS system.
+
+## The Build Environment
+
+Please download and install Xcode from App Store on the MacOS system.
+After a successful installation, we should be able to run the
+following command
+
+```bash
+xcodebuild -version
+```
+
+## Configure CMake Options
+
+A complete list of CMake options related to iOS is
+at
+[here](https://github.com/PaddlePaddle/Paddle/blob/develop/cmake/cross_compiling/ios.cmake).
+
+Some of these options are mandatory:
+
+- `CMAKE_SYSTEM_NAME`: The target platform; must be `iOS`.  This
+  setting would automatically trigger some more changes, including
+  `WITH_C_API=ON`, `WITH_GPU=OFF`, `WITH_AVX=OFF`, `WITH_PYTHON=OFF`,
+  `WITH_RDMA=OFF`.
+- `WITH_C_API`: If build the inference library; must be `ON`, because
+  that is the only way we support inference on iOS.
+- `WITH_SWIG_PY`: Must be `OFF` because we don't support that Python
+  programs calls into C/C++ programs via SWIG on iOS.
+
+Some optional configurations:
+
+- `IOS_PLATFORM`: could be `OS` or `SIMULATOR`.  The default value is `OS`.
+  - `OS`: the build result is supposed to run on an iPhone or an iPad
+    with a real ARM CPU.
+  - `SIMULATOR`: the build result can run on the x86 simulator
+    provided by Xcode.
+- `IOS_ARCH`: the value depends on that of `IOS_PLATFORM`:
+
+  | `IOS_PLATFORM` | `IOS_ARCH` |
+  |----------------|------------|
+  | `OS`           | armv7, armv7s, arm64 |
+  | `SIMULATOR`    | i386, x86_64 |
+
+- `IOS_DEPLOYMENT_TARGET`: The supported minimum iOS version.  The
+  default value is `7.0`.
+- `IOS_ENABLE_BITCODE`: If
+  use
+  [Bitcode](https://developer.apple.com/library/content/documentation/IDEs/Conceptual/AppDistributionGuide/AppThinning/AppThinning.html#//apple_ref/doc/uid/TP40012582-CH35-SW3).
+  The default value is `ON`.
+- `IOS_USE_VECLIB_FOR_BLAS`: If
+  use
+  [vecLib](https://developer.apple.com/documentation/accelerate/veclib),
+  a BLAS implementation for iOS.  The default value is `OFF`.
+- `IOS_DEVELOPMENT_ROOT`: If not specified, PaddlePaddle's build
+  system will set one according to the value of `IOS_PLATFORM`.
+- `IOS_SDK_ROOT`: The iOS SDK directory.  If not specified,
+  PaddlePaddle's build system will choose the most recent version in
+  the directory of `IOS_DEVELOPMENT_ROOT`.
+
+Other options:
+
+- `USE_EIGEN_FOR_BLAS`: If use Eigen.  It is only reasonable to set
+  this option when `IOS_USE_VECLIB_FOR_BLAS=OFF`.
+- `HOST_C/CXX_COMPILER`: The host C/C++ compiler.  The default value
+  is the value of the environment variable `CC/CXX`, or `cc` and `c++`
+  respectively.
+
+
+Here follows a commonly-used cmake configuration that builds binaries
+for iPhone and iPad:
+
+```bash
+cmake -DCMAKE_SYSTEM_NAME=iOS \
+      -DIOS_PLATFORM=OS \
+      -DIOS_ARCH="armv7;arm64" \
+      -DIOS_ENABLE_BITCODE=ON \
+      -DIOS_USE_VECLIB_FOR_BLAS=ON \
+      -DCMAKE_INSTALL_PREFIX=your/path/to/install \
+      -DWITH_C_API=ON \
+      -DWITH_TESTING=OFF \
+      -DWITH_SWIG_PY=OFF \
+      ..
+```
+
+
+Here follows another configuration that builds binaries for the
+simulator:
+
+```bash
+cmake -DCMAKE_SYSTEM_NAME=iOS \
+      -DIOS_PLATFORM=SIMULATOR \
+      -DIOS_ARCH="x86_64" \
+      -DIOS_USE_VECLIB_FOR_BLAS=ON \
+      -DCMAKE_INSTALL_PREFIX=your/path/to/install \
+      -DWITH_C_API=ON \
+      -DWITH_TESTING=OFF \
+      -DWITH_SWIG_PY=OFF \
+      ..
+```
+
+If we want to minimize the size of the generated binary files，we can
+set `CMAKE_BUILD_TYPE=MinSizeRel`.  Or, if we want to optimize for
+runtime performance, we can set `CMAKE_BUILD_TYPE=Release` and/or
+`IOS_USE_VECLIB_FOR_BLAS=ON`.  We can also set `CMAKE_C/CXX_FLAGS` to
+have more control of the building process.
+
+
+## Build and Install
+
+After the cmake command completes, run the following commands to
+download third-party dependencies and build PaddlePaddle:
+
+```
+$ make
+$ make install
+```
+
+Please be aware that if you had been built for other platforms, please
+`rm -rf build` so to remove all existing intermediate build results.
+
+After `make install`, you will find the following content in
+`your/path/to/install`:
+
+- `include`: the header files of the inference library,
+- `lib`: the inference library,
+- `third_party`: all built third-party libraries.
+
+We can build a version that supports real iOS hardware and the
+simulator, by building the IOS and SIMULATOR version separately, and
+merge them using `lipo`.