프로그램 사용/gcc2021. 7. 8. 10:40

귀찮으니 날로먹는 코딩으로 테스트

$ cat 1.c
#include <stdio.h>

void main()
{
        unsigned char a = 0xFF;
        char b =a;
        short c = a;
        short d = (char)a;
        short e = (int)a;

        int f = a;
        int g = (int)a;
        int h = (int)(char)a;

        printf("a %d\n",a);
        printf("a %d\n",(int)a);
        printf("a %d\n",(char)a);
        printf("b %d\n",b);
        printf("c %d\n",c);
        printf("d %d\n",d);
        printf("e %d\n",e);
        printf("f %d\n",f);
        printf("g %d\n",g);
        printf("h %d\n",h);
}

 

컴파일러 버전과 아키텍쳐, 그리고 결과인데... 머냐..?!?!

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 9.3.0-17ubuntu1~20.04' --with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,gm2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-9 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none=/build/gcc-9-HskZEa/gcc-9-9.3.0/debian/tmp-nvptx/usr,hsa --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)
$ arm-linux-gnueabihf-gcc -v
Using built-in specs.
COLLECT_GCC=arm-linux-gnueabihf-gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc-cross/arm-linux-gnueabihf/7/lto-wrapper
Target: arm-linux-gnueabihf
Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 7.5.0-3ubuntu1~18.04' --with-bugurl=file:///usr/share/doc/gcc-7/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-7 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm --disable-libquadmath --disable-libquadmath-support --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-multiarch --enable-multilib --disable-sjlj-exceptions --with-arch=armv7-a --with-fpu=vfpv3-d16 --with-float=hard --with-mode=thumb --disable-werror --enable-multilib --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=arm-linux-gnueabihf --program-prefix=arm-linux-gnueabihf- --includedir=/usr/arm-linux-gnueabihf/include
Thread model: posix
gcc version 7.5.0 (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04)
$ ./1
a 255
a 255
a -1
b -1
c 255
d -1
e 255
f 255
g 255
h -1
# /mnt/1
a 255
a 255
a 255
b 255
c 255
d 255
e 255
f 255
g 255

 

라즈베리 파이 4에서 시도. arm 아키텍쳐용 컴파일러의 특성인가?

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/aarch64-linux-gnu/8/lto-wrapper
Target: aarch64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 8.3.0-6' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-8 --program-prefix=aarch64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libquadmath --disable-libquadmath-support --enable-plugin --enable-default-pie --with-system-zlib --disable-libphobos --enable-multiarch --enable-fix-cortex-a53-843419 --disable-werror --enable-checking=release --build=aarch64-linux-gnu --host=aarch64-linux-gnu --target=aarch64-linux-gnu
Thread model: posix
gcc version 8.3.0 (Debian 8.3.0-6)
$ ./1
a 255
a 255
a 255
b 255
c 255
d 255
e 255
f 255
g 255
h 255

 

+

두개중에 하나만 주면 되는진 모르겠지만, 둘 다 주거나 -fsigned-char 만 주어도 결과가 -1로 나오긴 한다.

원문으로 보니 --signed-chars는 RVCT 컴파일러를 위한 옵션인 듯.

The ANSI C standard specifies a range for both signed (at least -127 to +127) and unsigned (at least 0 to 255) chars. Simple chars are not specifically defined and it is compiler dependent whether they are signed or unsigned. Although the ARM architecture has the LDRSB instruction, that loads a signed byte into a 32-bit register with sign extension, the earliest versions of the architecture did not. It made sense at the time for the compiler to treat simple chars as unsigned, whereas on the x86 simple chars are, by default, treated as signed.
One workaround for users of GCC is to use the -fsigned-char command line switch or --signed-chars for RVCT, that forces all chars to become signed, but a better practice is to write portable code by declaring char variables appropriately. Unsigned char must be used for accessing memory as a block of bytes or for small unsigned integers. Signed char must be used for small signed integers and simple char must be used only for ASCII characters and strings. In fact, on an ARM core, it is usually better to use ints rather than chars, even for small values, for performance reasons. You can read more on this in Optimizing Code to Run on ARM Processors.

[링크 : https://developer.arm.com/.../Miscellaneous-C-porting-issues/unsigned-char-and-signed-char]

 

LDRSB (Thumb*) - Load Register Signed Byte

[링크 : http://qcd.phys.cmu.edu/QCDcluster/intel/vtune/reference/LDRSB_(Thumb).htm]

 

LDRB - Load Register Byte

[링크 : http://qcd.phys.cmu.edu/QCDcluster/intel/vtune/reference/INST_LDRB.htm]

 

char -> signed char: -fsigned-char == -fno-unsigned-char
char -> unsigned char: -funsigned-char == -fno-signed-char

[링크 : https://jooojub.github.io/gcc-options-fsigned-char/]

 

-fsigned-char
Let the type char be signed, like signed char.
Note that this is equivalent to -fno-unsigned-char, which is the negative form of -funsigned-char. Likewise, the option -fno-signed-char is equivalent to -funsigned-char.

-funsigned-char
Let the type char be unsigned, like unsigned char.
Each kind of machine has a default for what char should be. It is either like unsigned char by default or like signed char by default.
Ideally, a portable program should always use signed char or unsigned char when it depends on the signedness of an object. But many programs have been written to use plain char and expect it to be signed, or expect it to be unsigned, depending on the machines they were written for. This option, and its inverse, let you make such a program work with the opposite default.
The type char is always a distinct type from each of signed char or unsigned char, even though its behavior is always just like one of those two.

[링크 : https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html]

 

+

2021.07.09

으잉? singed char로 하면 되긴 한다. char가 signed 아니었어?!

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프로그램 사용/gcc2021. 6. 30. 11:43

-O3 하면 자동으로 -ftree-vectorize가 추가되었다고.

아무튼 연산만 하고 출력을 안하니 사용하지 않는 코드로 해서 vadd가 안나와서 한참을 헤맸네..

 

$ g++ -O3 -mavx autovector.cpp -fopt-info-vec-all
autovector.cpp:22:22: missed: couldn't vectorize loop
autovector.cpp:25:19: missed: not vectorized: complicated access pattern.
autovector.cpp:23:21: missed: couldn't vectorize loop
autovector.cpp:25:14: missed: not vectorized: complicated access pattern.
autovector.cpp:16:23: optimized: loop vectorized using 32 byte vectors
autovector.cpp:10:5: note: vectorized 1 loops in function.
autovector.cpp:15:43: missed: statement clobbers memory: now = std::chrono::_V2::system_clock::now ();
autovector.cpp:27:77: missed: statement clobbers memory: D.189348 = std::chrono::_V2::system_clock::now ();
autovector.cpp:28:2: missed: statement clobbers memory: __assert_fail ("result[2] == ( 2.0f + 0.1335f)+( 1.50f*2.0f + 0.9383f)-(0.33f*2.0f+0.1172f)+3*(float)(noTests-1)", "autovector.cpp", 28, "int main()");
/usr/include/c++/9/ostream:570:18: missed: statement clobbers memory: std::__ostream_insert<char, std::char_traits<char> > (&cout, "CG> message -channel \"exercise results\" Time used: ", 51);
/usr/include/c++/9/ostream:221:29: missed: statement clobbers memory: _46 = std::basic_ostream<char>::_M_insert<double> (&cout, _42);
/usr/include/c++/9/ostream:570:18: missed: statement clobbers memory: std::__ostream_insert<char, std::char_traits<char> > (_46, "s, N * noTests=", 15);
autovector.cpp:29:112: missed: statement clobbers memory: _35 = std::basic_ostream<char>::operator<< (_46, 2000000000);
/usr/include/c++/9/ostream:113:13: missed: statement clobbers memory: std::endl<char, std::char_traits<char> > (_35);
/usr/include/c++/9/iostream:74:25: missed: statement clobbers memory: std::ios_base::Init::Init (&__ioinit);
/usr/include/c++/9/iostream:74:25: missed: statement clobbers memory: __cxa_atexit (__dt_comp , &__ioinit, &__dso_handle);
$ gcc -mcpu=native -march=native -Q --help=target
The following options are target specific:
  -mabi=                                aapcs-linux
  -mabort-on-noreturn                   [disabled]
  -mandroid                             [disabled]
  -mapcs                                [disabled]
  -mapcs-frame                          [disabled]
  -mapcs-reentrant                      [disabled]
  -mapcs-stack-check                    [disabled]
  -march=                               armv7ve+vfpv3-d16
  -marm                                 [enabled]
  -masm-syntax-unified                  [disabled]
  -mbe32                                [enabled]
  -mbe8                                 [disabled]
  -mbig-endian                          [disabled]
  -mbionic                              [disabled]
  -mbranch-cost=                        -1
  -mcallee-super-interworking           [disabled]
  -mcaller-super-interworking           [disabled]
  -mcmse                                [disabled]
  -mcpu=                                cortex-a7
  -mfix-cortex-m3-ldrd                  [disabled]
  -mflip-thumb                          [disabled]
  -mfloat-abi=                          hard
  -mfp16-format=                        none
  -mfpu=                                vfp
  -mglibc                               [enabled]
  -mhard-float
  -mlittle-endian                       [enabled]
  -mlong-calls                          [disabled]
  -mmusl                                [disabled]
  -mneon-for-64bits                     [disabled]
  -mpic-data-is-text-relative           [enabled]
  -mpic-register=
  -mpoke-function-name                  [disabled]
  -mprint-tune-info                     [disabled]
  -mpure-code                           [disabled]
  -mrestrict-it                         [disabled]
  -msched-prolog                        [enabled]
  -msingle-pic-base                     [disabled]
  -mslow-flash-data                     [disabled]
  -msoft-float
  -mstructure-size-boundary=            8
  -mthumb                               [disabled]
  -mthumb-interwork                     [disabled]
  -mtls-dialect=                        gnu
  -mtp=                                 cp15
  -mtpcs-frame                          [disabled]
  -mtpcs-leaf-frame                     [disabled]
  -mtune=
  -muclibc                              [disabled]
  -munaligned-access                    [enabled]
  -mvectorize-with-neon-double          [disabled]
  -mvectorize-with-neon-quad            [enabled]
  -mword-relocations                    [disabled]

  Known ARM ABIs (for use with the -mabi= option):
    aapcs aapcs-linux apcs-gnu atpcs iwmmxt

  Known __fp16 formats (for use with the -mfp16-format= option):
    alternative ieee none

  Known ARM FPUs (for use with the -mfpu= option):
    auto crypto-neon-fp-armv8 fp-armv8 fpv4-sp-d16 fpv5-d16 fpv5-sp-d16 neon neon-fp-armv8 neon-fp16 neon-vfpv3 neon-vfpv4 vfp vfp3 vfpv2 vfpv3 vfpv3-d16 vfpv3-d16-fp16 vfpv3-fp16 vfpv3xd
    vfpv3xd-fp16 vfpv4 vfpv4-d16

  Valid arguments to -mtp=:
    auto cp15 soft

  Known floating-point ABIs (for use with the -mfloat-abi= option):
    hard soft softfp

  TLS dialect to use:
    gnu gnu2


[링크 : https://www.raspberrypi.org/forums/viewtopic.php?t=155461]

[링크 : https://www.codingame.com/playgrounds/283/sse-avx-vectorization/autovectorization]

 

+

$ cat neon.c
#include <stdio.h>

void main()
{
        int a[256];
        int b[256];
        int c[256];

        int i;
        for(i = 0; i < 256; i++)
        {
                a[i] = b[i] + c[i];
        }

        printf("%d %d %d\n", a[0], b[0], c[0]);
}

 

$ gcc -O3 neon.c -mfpu=neon
$ objdump -d a.out  | grep v
   10320:       e1a01000        mov     r1, r0
   10328:       e1a0300d        mov     r3, sp
   1032c:       f4610add        vld1.64 {d16-d17}, [r1 :64]!
   10330:       f4622add        vld1.64 {d18-d19}, [r2 :64]!
   10334:       f26008e2        vadd.i32        q8, q8, q9
   10338:       f4430add        vst1.64 {d16-d17}, [r3 :64]!
   10360:       e3a0b000        mov     fp, #0
   10364:       e3a0e000        mov     lr, #0
   1036c:       e1a0200d        mov     r2, sp
   1043c:       e3a03001        mov     r3, #1
   10454:       e1a07000        mov     r7, r0
   1046c:       e1a08001        mov     r8, r1
   10470:       e1a09002        mov     r9, r2
   10480:       e3a04000        mov     r4, #0
   1048c:       e1a02009        mov     r2, r9
   10490:       e1a01008        mov     r1, r8
   10494:       e1a00007        mov     r0, r7

 

$ gcc neon.c -mfpu=neon
$ objdump -d a.out  | grep v
   10318:       e3a0b000        mov     fp, #0
   1031c:       e3a0e000        mov     lr, #0
   10324:       e1a0200d        mov     r2, sp
   103f4:       e3a03001        mov     r3, #1
   10418:       e3a03000        mov     r3, #0
   10490:       e1a00000        nop                     ; (mov r0, r0)
   104a4:       e1a07000        mov     r7, r0
   104bc:       e1a08001        mov     r8, r1
   104c0:       e1a09002        mov     r9, r2
   104d0:       e3a04000        mov     r4, #0
   104dc:       e1a02009        mov     r2, r9
   104e0:       e1a01008        mov     r1, r8
   104e4:       e1a00007        mov     r0, r7

 

-fopt-info-vec-all 추가. -all 때문인지 어마어마하게 나오네

-fopt-info-vec 으로만 하니 깔끔하게 vectorized 라고 뜬다.

$ gcc neon.c -mfpu=neon -fopt-info-vec -O3
neon.c:10:2: note: loop vectorized

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프로그램 사용/gcc2021. 6. 22. 19:15

예전에는 문제없이 unsigned char에 대한 int 형으로의 캐스팅이 문제없이 되었던 것 같은데 안되서

C99나 C11의 영향인지 조금 더 찾아보는 중.

 

[링크 : https://gcc.gnu.org/onlinedocs/gcc/Characters-implementation.html#Characters-implementationl]

[링크 : https://gcc.gnu.org/onlinedocs/gcc/Integers-implementation.html]

[링크 : https://gcc.gnu.org/wiki/NewWconversion]

 

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프로그램 사용/gcc2021. 5. 7. 17:30

%p로 출력하니 0일 경우 (nil)로 출력되네?

 

[링크 : https://stackoverflow.com/questions/4744650/nil-pointer-in-c-c]

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프로그램 사용/gcc2021. 4. 8. 12:02

와.. 먼가 쓸데없는 뻘짓 ㅋㅋㅋ

 

makefile 에서 \" \" 로 감싸주니 의외로 간단하게 해결

#CROSS_PREFIX	= arm-buildroot-linux-gnueabihf
CFLAGS			= $(INCLUDEDIRS) -o -W -Wall -O2 -DCROSS_PREFIX=\"$(CROSS_PREFIX)\"

 

테스트 코드

void main()
{
    printf("%s\n", CROSS_PREFIX);
}

 

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프로그램 사용/gcc2021. 3. 25. 16:53

어떤게 변환되는지도 확인이 가능한 듯.

-ftree-vectorizer-verbose=[n] controls vectorization reports, with n ranging from 0 (no information reported) to 6 (all information reported).

 

25가지 예가 있는데 for a = b + c 같은건 된다고 한다.

Example 12: Induction:
Example 13: Outer-loop:
Example 14: Double reduction:
Example 15: Condition in nested loop:
Example 16: Load permutation in loop-aware SLP:
Example 17: Basic block SLP:
Example 18: Simple reduction in SLP:
Example 19: Reduction chain in SLP:
Example 20: Basic block SLP with multiple types, loads with different offsets, misaligned load, and not-affine Example 21: Backward access:
Example 22: Alignment hints:
Example 23: Widening shift:
Example 24: Condition with mixed types:
Example 25: Loop with bool:

[링크 : https://gcc.gnu.org/projects/tree-ssa/vectorization.html#using]

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프로그램 사용/gcc2021. 1. 24. 11:24

오늘도 어김없이(?) 노인학대 옵션 찾는중

3.19.59 x86 Options
These ‘-m’ options are defined for the x86 family of computers.

-march=cpu-type
‘sandybridge’
Intel Sandy Bridge CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, SSE4.2, POPCNT, AVX, AES and PCLMUL instruction set support.

[링크 : https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html]

 

+

그래도 tensorflow 빌드 해서 실행하는데 속도에 유의미한 영향을 주진 않네

이런 라즈베리 파이 만도 못한 내 노트북 ㅠㅠㅠㅠ

(라즈베리 4코어 + neon 가속시  170ms 정도, i5-2520m 에서 1300ms ㅠㅠ)

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프로그램 사용/gcc2021. 1. 19. 11:00

 

tensorflow lite 빌드해서 static libaray 로 libtensorflow-lite.a는 얻어냈는데

얘를 링크해서 빌드하니 dynamic link가 된다.

 

궁금해서 hello.cpp 이런거 하나 구해서 g++로 빌드하니

무조건 끌어가는 것 같긴한데

$ cat hello.cpp
// hello.cpp file
#include <iostream>
int main()
{
    std::cout << "Hello Geek\n";
    return 0;
}

$ g++ hello.cpp
$ ldd a.out
        linux-vdso.so.1 (0x7efa4000)
        /usr/lib/arm-linux-gnueabihf/libarmmem-${PLATFORM}.so => /usr/lib/arm-linux-gnueabihf/libarmmem-v7l.so (0x76f7e000)
        libstdc++.so.6 => /usr/lib/arm-linux-gnueabihf/libstdc++.so.6 (0x76e19000)
        libm.so.6 => /lib/arm-linux-gnueabihf/libm.so.6 (0x76d97000)
        libgcc_s.so.1 => /lib/arm-linux-gnueabihf/libgcc_s.so.1 (0x76d6a000)
        libc.so.6 => /lib/arm-linux-gnueabihf/libc.so.6 (0x76c1c000)
        /lib/ld-linux-armhf.so.3 (0x76f93000)

 

혹시나 해서 g++ -static 옵션을 주니 되긴 되네..

$ g++ hello.cpp -o b.out -static
$ ldd b.out
        not a dynamic executable

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프로그램 사용/gcc2020. 11. 24. 11:12

intel xeon Phi (KNL) 이나 Nvidia PTX 그리고 AMD HSAIL을 지원하는 predictive 라고 해도 먼 소리인지 모르겠다.

 

 

[링크 : https://gcc.gnu.org/wiki/Offloading]

[링크 : https://gcc.gnu.org/wiki/nvptx]

[링크 : https://gcc.gnu.org/wiki/OpenACC]

 

[링크 : https://repository.kisti.re.kr/bitstream/10580/6542/1/2014-147%20Slurm%20관리자%20이용자%20가이드.pdf]

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프로그램 사용/gcc2020. 10. 21. 12:47

gcc 4.4 이후 버전 사용가능

#pragma GCC push_options
#pragma GCC optimize ("O0")

your code

#pragma GCC pop_options

 

void __attribute__((optimize("O0"))) foo(unsigned char data) {
    // unmodifiable compiler code
}

[링크 : https://stackoverflow.com/questions/2219829/how-to-prevent-gcc-optimizing-some-statements-in-c]

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