C++ always_inline

本文详细解析了C/C++中always_inline属性的作用与原理。它能显著提升函数调用速度,通过将函数直接嵌入调用处,避免了函数调用的开销,但可能会增加代码体积。文章提醒开发者谨慎使用此特性,以防代码膨胀。

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always_inline
  • atrribute((always_inline))
  • 强制内联。所有加了该语句的函数,在编译时会作为内联函数被使用(不会被编译成函数调用方式,而是直接嵌入到调用函数体内)。
  • 会加快函数调用的速度,但会增加函数体的大小(相当于把代码直接copy过去)。慎用。
__attribute((always_inline) void a()
{
    // ...    
}

void b()
{
    a();
}
ny@wxsc07:~/new/dxp_test_bak - new$ make clean && make CFLAGS="-g" rm -f main.o src/generate_box_pairs.so src/info_partition.so src/output_bin.so src/get_org_info.so src/generate_box_pairs.o src/info_partition.o src/output_bin.o src/get_org_info.o dxp_test mpic++ -I ./include -I /tools/Xilinx/Vitis_HLS/2022.2/include/ -O3 -fPIC -c main.cpp -o main.o In file included from ./include/md_fix.h:5, from main.cpp:7: ./include/ppip_float.h:7: warning: "__always_inline" redefined 7 | #define __always_inline //__attribute__((always_inline)) inline | In file included from /usr/include/features.h:461, from /usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33, from /usr/include/stdio.h:27, from main.cpp:1: /usr/include/x86_64-linux-gnu/sys/cdefs.h:319: note: this is the location of the previous definition 319 | # define __always_inline __inline __attribute__ ((__always_inline__)) | mpic++ -I ./include -I /tools/Xilinx/Vitis_HLS/2022.2/include/ -O3 -fPIC -c src/generate_box_pairs.cpp -o src/generate_box_pairs.o In file included from ./include/md_fix.h:5, from src/generate_box_pairs.cpp:1: ./include/ppip_float.h:7: warning: "__always_inline" redefined 7 | #define __always_inline //__attribute__((always_inline)) inline | In file included from /usr/include/features.h:461, from /usr/include/x86_64-linux-gnu/c++/9/bits/os_defines.h:39, from /usr/include/x86_64-linux-gnu/c++/9/bits/c++config.h:528, from /usr/include/c++/9/bits/stl_algobase.h:59, from /usr/include/c++/9/deque:60, from /usr/include/c++/9/queue:60, from /tools/Xilinx/Vitis_HLS/2022.2/include/hls_stream.h:23, from ./include/md_fix.h:4, from src/generate_box_pairs.cpp:1: /usr/include/x86_64-linux-gnu/sys/cdefs.h:319: note: this is the location of the previous definition 31
03-26
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