gcc vectorized loop

-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