Halide学习笔记----Halide tutorial源码阅读10

Halide入门教程10

// Halide tutorial lesson 10: AOT compilation part 1
// Halide入门教程第十课：提前编译
// This lesson demonstrates how to use Halide as an more traditional
// ahead-of-time (AOT) compiler.
// 本课程展示了如何用Halide来充当一个传统的提前编译器

// This lesson is split across two files. The first (this one), builds
// a Halide pipeline and compiles it to a static library and
// header. The second (lesson_10_aot_compilation_run.cpp), uses that
// static library to actually run the pipeline. This means that
// compiling this code is a multi-step process.
// 本课程拆分成两个文件，第一个建立Halide pipeline，并且将它编译成静态链接库和相应的头文件，
// 第二个文件使用静态链接库来运行整个pipeline。这意味着编译这些代码要多个阶段的流程。

// On linux, you can compile and run it like so:
// g++ lesson_10*generate.cpp -g -std=c++11 -I ../include -L ../bin -lHalide -lpthread -ldl -o lesson_10_generate
// LD_LIBRARY_PATH=../bin ./lesson_10_generate
// g++ lesson_10*run.cpp lesson_10_halide.a -std=c++11 -I ../include -lpthread -ldl -o lesson_10_run
// ./lesson_10_run

// The benefits of this approach are that the final program:
// - Doesn't do any jit compilation at runtime, so it's fast.
// - Doesn't depend on libHalide at all, so it's a small, easy-to-deploy binary.
// 这种放出的好处是，最终生成的程序：
// 1.不需要做任何即时编译，因此很快
// 2.不依赖libHalide库，因此可执行程序很小，容易部署二进制文件

#include "Halide.h"
#include <stdio.h>
using namespace Halide;

int main(int argc, char **argv) {

// We'll define a simple one-stage pipeline:
Func brighter;
Var x, y;

// The pipeline will depend on one scalar parameter.
// 定义
4000
输入变量
Param<uint8_t> offset;

// And take one grayscale 8-bit input buffer. The first
// constructor argument gives the type of a pixel, and the second
// specifies the number of dimensions (not the number of
// channels!). For a grayscale image this is two; for a color
// image it's three. Currently, four dimensions is the maximum for
// inputs and outputs.
// 定义输入图像，构造函数的第一个变量定义图像数据类型，第二个变量定义图像通道数。
// 灰度图像为2通道的。当前Halide最大支持4通道的输入输出。
ImageParam input(type_of<uint8_t>(), 2);

// If we were jit-compiling, these would just be an int and a
// Buffer, but because we want to compile the pipeline once and
// have it work for any value of the parameter, we need to make a
// Param object, which can be used like an Expr, and an ImageParam
// object, which can be used like a Buffer.
// 如果是即时编译的话，这些就是int类型数据和Buffer，但是由于一次编译pipeline，然后对任何参数
// 都能工作，我们需要Param对象，它可以当做表达式一样使用，ImageParam可以当做Buffer一样使用

// Define the Func.
brighter(x, y) = input(x, y) + offset;

// Schedule it.
brighter.vectorize(x, 16).parallel(y);

// This time, instead of calling brighter.realize(...), which
// would compile and run the pipeline immediately, we'll call a
// method that compiles the pipeline to a static library and header.
// 显式调用函数来编译成静态链接库和对应的头文件
// For AOT-compiled code, we need to explicitly declare the
// arguments to the routine. This routine takes two. Arguments are
// usually Params or ImageParams.
// 对于提前便已代码，我们需要显示生命对应的输入参数。
brighter.compile_to_static_library("lesson_10_halide", {input, offset}, "brighter");

printf("Halide pipeline compiled, but not yet run.\n");

// To continue this lesson, look in the file lesson_10_aot_compilation_run.cpp

return 0;
}

这里需要特别说明的是compile_to_static_library函数，它的声明如下

EXPORT void Halide::Pipeline::compile_to_static_library (
const std::string &filename_prefix,                    //静态链接库和头文件名字的前缀
const std::vector< Argument > & args,                  // 函数的参数
const std::string & fn_name,                           // 函数名称
const Target &  target = get_target_from_environment() // 指定编译成哪种平台的代码，   x86/arm/...
)
//Compile to static-library file and header pair, with the given arguments.
// 在给定参数的情况下将对应文件编译成静态链接库和头文件

// Halide tutorial lesson 10: AOT compilation part 2
// Halide入门教程第十课：提前编译
// Before reading this file, see lesson_10_aot_compilation_generate.cpp

// This is the code that actually uses the Halide pipeline we've
// compiled. It does not depend on libHalide, so we won't be including
// Halide.h.
// 这部分代码才是实际上使用已经编译过的Halide pipeline.它并不依赖与libHalide。
// Instead, it depends on the header file that lesson_10_generate
// produced when we ran it:
// 但是它依赖于生成器生成的静态链接库和头文件
#include "lesson_10_halide.h"

// We want to continue to use our Halide::Buffer with AOT-compiled
// code, so we explicitly include it. It's a header-only class, and
// doesn't require libHalide.
#include "HalideBuffer.h"

#include <stdio.h>

int main(int argc, char **argv) {
// Have a look in the header file above (it won't exist until you've run
// lesson_10_generate). At the bottom is the signature of the function we generated:

// int brighter(halide_buffer_t *_input_buffer, uint8_t _offset, halide_buffer_t *_brighter_buffer);
// 查看生成器生成的头文件中函数的声明格式，按此格式调用函数。

// The ImageParam inputs have become pointers to "halide_buffer_t"
// structs. This is struct that Halide uses to represent arrays of
// data.  Unless you're calling the Halide pipeline from pure C
// code, you don't want to use it
// directly. Halide::Runtime::Buffer is a simple wrapper around
// halide_buffer_t that will implicitly convert to a
// halide_buffer_t *. We will pass Halide::Runtime::Buffer objects
// in those slots.

// The Halide::Buffer class we have been using in JIT code is in
// fact just a shared pointer to the simpler
// Halide::Runtime::Buffer class. They share the same API.

// Finally, the return value of "brighter" is an error code. It's
// zero on success.

// Let's make a buffer for our input and output.
Halide::Runtime::Buffer<uint8_t> input(640, 480), output(640, 480);

// Halide::Runtime::Buffer also has constructors that wrap
// existing data instead of allocating new memory. Use these if
// you have your own Image type that you want to use.

int offset = 5;
int error = brighter(input, offset, output); // 调用静态库中的代码

if (error) {
printf("Halide returned an error: %d\n", error);
return -1;
}

// Now let's check the filter performed as advertised. It was
// supposed to add the offset to every input pixel.
for (int y = 0; y < 480; y++) {
for (int x = 0; x < 640; x++) {
uint8_t input_val = input(x, y);
uint8_t output_val = output(x, y);
uint8_t correct_val = input_val + offset;
if (output_val != correct_val) {
printf("output(%d, %d) was %d instead of %d\n",
x, y, output_val, correct_val);
return -1;
}
}
}

// Everything worked!
printf("Success!\n");
return 0;
}

可以按照第一部分中代码提到的那样，在终端中逐步执行对应的命令，最后得到运行代码。

由于步骤繁多，在这里写成shell脚本，方便执行：

#!/usr/bin/bash
#########################################################################
# File Name: lesson_10_compile.sh
# Author: xxx
# Created Time: Fri 22 Dec 2017 09:56:20 PM CST
#########################################################################

echo "1. compile generator"
g++ lesson_10*generate.cpp -std=c++11 -I ../include -L ../bin -lHalide -lpthread -ldl -o lesson_10_generate
echo "2. generate static library"
./lesson_10_generate
echo "3. compile run to generate executive file"
g++ lesson_10*run.cpp lesson_10_halide.a -std=c++11 -I ../include -lpthread -ldl -o lesson_10_run
echo "4. test executive file"
./lesson_10_run

在终端中运行shell脚本

$ sh lesson_10_compile.sh

执行shell脚本



生成的生成器、静态链接库、头文件和可执行文件