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c – GCC 5及更高版本中的AVX2支持

作者:互联网

我写了下面的类“T”来加速对它的操纵
使用AVX2的“字符集”.然后我发现它不起作用
当我使用“-O3”时gcc 5及更高版本.
任何人都可以帮助我追溯到一些编程结构
众所周知,不会在最新的编译器/系统上工作?

这段代码是如何工作的:底层结构(“_bits”)是一个256字节的块(为AVX2对齐和分配),可以作为char [256]或AVX2元素访问,具体取决于是访问元素还是整个事物用于矢量运算.似乎它应该在AVX2平台上运行良好.没有?

这真的很难调试,因为“valgrind”说它很干净,
我不能使用调试器(因为问题消失了
我删除“-O3”).但是,我对“| =”的使用感到不满意
解决方法,因为如果这段代码真的错了,那我可能就是
在其他地方犯同样的错误并搞砸了一切
我开发!

值得注意的是“|”运算符有问题但是
“| =”没有.问题可能与从中返回结构有关
一个功能?但我认为返回一个结构自1990年以来一直有效
或者其他的东西.

// g++ -std=c++11 -mavx2 -O3 gcc_fail.cpp

#include "assert.h"
#include "immintrin.h" // AVX

class T {
public:
  __m256i _bits[8];
  inline bool& operator[](unsigned char c)       {return ((bool*)_bits)[c];}
  inline bool  operator[](unsigned char c) const {return ((bool*)_bits)[c];}
  inline          T()                   {}
  inline explicit T(char const*);
  inline T     operator| (T const& b) const;
  inline T &   operator|=(T const& b);
  inline bool  operator! ()           const;
};

T::T(char const* s)
{
  _bits[0] = _bits[1] = _bits[2] = _bits[3] = _mm256_set1_epi32(0);
  _bits[4] = _bits[5] = _bits[6] = _bits[7] = _mm256_set1_epi32(0);
  char c;
  while ((c = *s++))
    (*this)[c] = true;
}

T T::operator| (T const& b) const
{
  T res;
  for (int i = 0; i < 8; i++)
    res._bits[i] = _mm256_or_si256(_bits[i], b._bits[i]);


  // FIXME why does the above code fail with -O3 in new gcc?
  for (int i=0; i<256; i++)
    assert(res[i] == ((*this)[i] || b[i]));
  // gcc 4.7.0 - PASS
  // gcc 4.7.2 - PASS
  // gcc 4.8.0 - PASS
  // gcc 4.9.2 - PASS
  // gcc 5.2.0 - FAIL
  // gcc 5.3.0 - FAIL
  // gcc 5.3.1 - FAIL
  // gcc 6.1.0 - FAIL


  return res;
}

T & T::operator|=(T const& b)
{
  for (int i = 0; i < 8; i++)
    _bits[i] = _mm256_or_si256(_bits[i], b._bits[i]);
  return *this;
}

bool T::operator! () const
{
  for (int i = 0; i < 8; i++)
    if (!_mm256_testz_si256(_bits[i], _bits[i]))
      return false;
  return true;
}

int Main()
{
  T sep (" ,\t\n");
  T end ("");
  return !(sep|end);
}

int main()
{
  return Main();
}

解决方法:

您的代码的问题是当您应该使用unsigned char *时使用bool *,这允许GCC 5继续进行指针别名优化.

由GCC 4.8.5和5.3.1生成的函数Main()的机器代码的两个转储在本附录的答案末尾供参考.

看代码:

反编译

在序幕之后,T sep的_bits被初始化为零……

  _bits[0] = _bits[1] = _bits[2] = _bits[3] = _mm256_set1_epi32(0);
  _bits[4] = _bits[5] = _bits[6] = _bits[7] = _mm256_set1_epi32(0);

  40063d:       c5 fd 7f 44 24 60               vmovdqa %ymm0,0x60(%rsp)
  400643:       c5 fd 7f 44 24 40               vmovdqa %ymm0,0x40(%rsp)
  400649:       c5 fd 7f 44 24 20               vmovdqa %ymm0,0x20(%rsp)
  40064f:       c5 fd 7f 04 24                  vmovdqa %ymm0,(%rsp)
  400654:       c5 fd 7f 84 24 e0 00 00 00      vmovdqa %ymm0,0xe0(%rsp)
  40065d:       c5 fd 7f 84 24 c0 00 00 00      vmovdqa %ymm0,0xc0(%rsp)
  400666:       c5 fd 7f 84 24 a0 00 00 00      vmovdqa %ymm0,0xa0(%rsp)
  40066f:       c5 fd 7f 84 24 80 00 00 00      vmovdqa %ymm0,0x80(%rsp)

然后在基于char * s的循环中写入.

  char c;
  while ((c = *s++))
    (*this)[c] = true;

  400680:       48 83 c2 01                     add    $0x1,%rdx
  400684:       c6 04 04 01                     movb   $0x1,(%rsp,%rax,1)
  400688:       0f b6 42 ff                     movzbl -0x1(%rdx),%eax
  40068c:       84 c0                           test   %al,%al
  40068e:       75 f0                           jne    400680 <_Z4Mainv+0x60>

两个编译器然后将T end初始化为0:

  400690:       c5 f9 ef c0                     vpxor  %xmm0,%xmm0,%xmm0
  400694:       31 c0                           xor    %eax,%eax
  400696:       c5 fd 7f 84 24 60 01 00 00      vmovdqa %ymm0,0x160(%rsp)
  40069f:       c5 fd 7f 84 24 40 01 00 00      vmovdqa %ymm0,0x140(%rsp)
  4006a8:       c5 fd 7f 84 24 20 01 00 00      vmovdqa %ymm0,0x120(%rsp)
  4006b1:       c5 fd 7f 84 24 00 01 00 00      vmovdqa %ymm0,0x100(%rsp)
  4006ba:       c5 fd 7f 84 24 e0 01 00 00      vmovdqa %ymm0,0x1e0(%rsp)
  4006c3:       c5 fd 7f 84 24 c0 01 00 00      vmovdqa %ymm0,0x1c0(%rsp)
  4006cc:       c5 fd 7f 84 24 a0 01 00 00      vmovdqa %ymm0,0x1a0(%rsp)
  4006d5:       c5 fd 7f 84 24 80 01 00 00      vmovdqa %ymm0,0x180(%rsp)

然后两个编译器都优化了_mm256_or_si256()操作,因为已知T端为0.但是,GCC 4.8.5从T sep复制到T res(计算上当你将OR变成零变量时会发生什么),而GCC 5.3.1将T res初始化为0.它有权这样做,因为在您的operator []方法中,您将类型为__m256i *的指针强制转换为bool *,并允许编译器假定指针不是别名.因此,在GCC 4.8.5中你看到了

  4006de:       c5 fd 6f 04 24                  vmovdqa (%rsp),%ymm0
  4006e3:       c5 fd 7f 84 24 00 02 00 00      vmovdqa %ymm0,0x200(%rsp)
  4006ec:       c5 fd 6f 44 24 20               vmovdqa 0x20(%rsp),%ymm0
  4006f2:       c5 fd 7f 84 24 20 02 00 00      vmovdqa %ymm0,0x220(%rsp)
  4006fb:       c5 fd 6f 44 24 40               vmovdqa 0x40(%rsp),%ymm0
  400701:       c5 fd 7f 84 24 40 02 00 00      vmovdqa %ymm0,0x240(%rsp)
  40070a:       c5 fd 6f 44 24 60               vmovdqa 0x60(%rsp),%ymm0
  400710:       c5 fd 7f 84 24 60 02 00 00      vmovdqa %ymm0,0x260(%rsp)
  400719:       c5 fd 6f 84 24 80 00 00 00      vmovdqa 0x80(%rsp),%ymm0
  400722:       c5 fd 7f 84 24 80 02 00 00      vmovdqa %ymm0,0x280(%rsp)
  40072b:       c5 fd 6f 84 24 a0 00 00 00      vmovdqa 0xa0(%rsp),%ymm0
  400734:       c5 fd 7f 84 24 a0 02 00 00      vmovdqa %ymm0,0x2a0(%rsp)
  40073d:       c5 fd 6f 84 24 c0 00 00 00      vmovdqa 0xc0(%rsp),%ymm0
  400746:       c5 fd 7f 84 24 c0 02 00 00      vmovdqa %ymm0,0x2c0(%rsp)
  40074f:       c5 fd 6f 84 24 e0 00 00 00      vmovdqa 0xe0(%rsp),%ymm0
  400758:       c5 fd 7f 84 24 e0 02 00 00      vmovdqa %ymm0,0x2e0(%rsp)

而在GCC 5.3.1中你看到了

  4006fa:       c5 fd 7f 85 f0 fe ff ff         vmovdqa %ymm0,-0x110(%rbp)
  400702:       c5 fd 7f 85 10 ff ff ff         vmovdqa %ymm0,-0xf0(%rbp)
  40070a:       c5 fd 7f 85 30 ff ff ff         vmovdqa %ymm0,-0xd0(%rbp)
  400712:       c5 fd 7f 85 50 ff ff ff         vmovdqa %ymm0,-0xb0(%rbp)
  40071a:       c5 fd 7f 85 70 ff ff ff         vmovdqa %ymm0,-0x90(%rbp)
  400722:       c5 fd 7f 45 90                  vmovdqa %ymm0,-0x70(%rbp)
  400727:       c5 fd 7f 45 b0                  vmovdqa %ymm0,-0x50(%rbp)
  40072c:       c5 fd 7f 45 d0                  vmovdqa %ymm0,-0x30(%rbp)

因此,assert()的读取失败.

标准对指针别名的裁决:

ISO C 11引用了以下部分的别名,这表明使用bool *无法访问__m256i *类型的变量,但可以使用char * / unsigned char *访问:

§ 3.10 Lvalues and rvalues [basic.lval]

[…]

If a program attempts to access the stored value of an object through a glvalue of other than one of the following types the behavior is undefined: [52]

  • the dynamic type of the object,
  • a cv-qualified version of the dynamic type of the object,
  • a type similar (as defined in 4.4) to the dynamic type of the object,
  • a type that is the signed or unsigned type corresponding to the dynamic type of the object,
  • a type that is the signed or unsigned type corresponding to a cv-qualified version of the dynamic type of the object,
  • an aggregate or union type that includes one of the aforementioned types among its elements or non-static data members (including, recursively, an element or non-static data member of a subaggregate or contained union),
  • a type that is a (possibly cv-qualified) base class type of the dynamic type of the object,
  • a char or unsigned char type.

52) The intent of this list is to specify those circumstances in which an object may or may not be aliased.

附录

GCC 4.8.5:

0000000000400620 <_Z4Mainv>:
  400620:       55                              push   %rbp
  400621:       c5 f9 ef c0                     vpxor  %xmm0,%xmm0,%xmm0
  400625:       ba e5 08 40 00                  mov    $0x4008e5,%edx
  40062a:       b8 20 00 00 00                  mov    $0x20,%eax
  40062f:       48 89 e5                        mov    %rsp,%rbp
  400632:       48 83 e4 e0                     and    $0xffffffffffffffe0,%rsp
  400636:       48 81 ec 00 03 00 00            sub    $0x300,%rsp
  40063d:       c5 fd 7f 44 24 60               vmovdqa %ymm0,0x60(%rsp)
  400643:       c5 fd 7f 44 24 40               vmovdqa %ymm0,0x40(%rsp)
  400649:       c5 fd 7f 44 24 20               vmovdqa %ymm0,0x20(%rsp)
  40064f:       c5 fd 7f 04 24                  vmovdqa %ymm0,(%rsp)
  400654:       c5 fd 7f 84 24 e0 00 00 00      vmovdqa %ymm0,0xe0(%rsp)
  40065d:       c5 fd 7f 84 24 c0 00 00 00      vmovdqa %ymm0,0xc0(%rsp)
  400666:       c5 fd 7f 84 24 a0 00 00 00      vmovdqa %ymm0,0xa0(%rsp)
  40066f:       c5 fd 7f 84 24 80 00 00 00      vmovdqa %ymm0,0x80(%rsp)
  400678:       0f 1f 84 00 00 00 00 00         nopl   0x0(%rax,%rax,1)
  400680:       48 83 c2 01                     add    $0x1,%rdx
  400684:       c6 04 04 01                     movb   $0x1,(%rsp,%rax,1)
  400688:       0f b6 42 ff                     movzbl -0x1(%rdx),%eax
  40068c:       84 c0                           test   %al,%al
  40068e:       75 f0                           jne    400680 <_Z4Mainv+0x60>
  400690:       c5 f9 ef c0                     vpxor  %xmm0,%xmm0,%xmm0
  400694:       31 c0                           xor    %eax,%eax
  400696:       c5 fd 7f 84 24 60 01 00 00      vmovdqa %ymm0,0x160(%rsp)
  40069f:       c5 fd 7f 84 24 40 01 00 00      vmovdqa %ymm0,0x140(%rsp)
  4006a8:       c5 fd 7f 84 24 20 01 00 00      vmovdqa %ymm0,0x120(%rsp)
  4006b1:       c5 fd 7f 84 24 00 01 00 00      vmovdqa %ymm0,0x100(%rsp)
  4006ba:       c5 fd 7f 84 24 e0 01 00 00      vmovdqa %ymm0,0x1e0(%rsp)
  4006c3:       c5 fd 7f 84 24 c0 01 00 00      vmovdqa %ymm0,0x1c0(%rsp)
  4006cc:       c5 fd 7f 84 24 a0 01 00 00      vmovdqa %ymm0,0x1a0(%rsp)
  4006d5:       c5 fd 7f 84 24 80 01 00 00      vmovdqa %ymm0,0x180(%rsp)
  4006de:       c5 fd 6f 04 24                  vmovdqa (%rsp),%ymm0
  4006e3:       c5 fd 7f 84 24 00 02 00 00      vmovdqa %ymm0,0x200(%rsp)
  4006ec:       c5 fd 6f 44 24 20               vmovdqa 0x20(%rsp),%ymm0
  4006f2:       c5 fd 7f 84 24 20 02 00 00      vmovdqa %ymm0,0x220(%rsp)
  4006fb:       c5 fd 6f 44 24 40               vmovdqa 0x40(%rsp),%ymm0
  400701:       c5 fd 7f 84 24 40 02 00 00      vmovdqa %ymm0,0x240(%rsp)
  40070a:       c5 fd 6f 44 24 60               vmovdqa 0x60(%rsp),%ymm0
  400710:       c5 fd 7f 84 24 60 02 00 00      vmovdqa %ymm0,0x260(%rsp)
  400719:       c5 fd 6f 84 24 80 00 00 00      vmovdqa 0x80(%rsp),%ymm0
  400722:       c5 fd 7f 84 24 80 02 00 00      vmovdqa %ymm0,0x280(%rsp)
  40072b:       c5 fd 6f 84 24 a0 00 00 00      vmovdqa 0xa0(%rsp),%ymm0
  400734:       c5 fd 7f 84 24 a0 02 00 00      vmovdqa %ymm0,0x2a0(%rsp)
  40073d:       c5 fd 6f 84 24 c0 00 00 00      vmovdqa 0xc0(%rsp),%ymm0
  400746:       c5 fd 7f 84 24 c0 02 00 00      vmovdqa %ymm0,0x2c0(%rsp)
  40074f:       c5 fd 6f 84 24 e0 00 00 00      vmovdqa 0xe0(%rsp),%ymm0
  400758:       c5 fd 7f 84 24 e0 02 00 00      vmovdqa %ymm0,0x2e0(%rsp)
  400761:       0f 1f 80 00 00 00 00            nopl   0x0(%rax)
  400768:       80 3c 04 00                     cmpb   $0x0,(%rsp,%rax,1)
  40076c:       0f b6 8c 04 00 02 00 00         movzbl 0x200(%rsp,%rax,1),%ecx
  400774:       ba 01 00 00 00                  mov    $0x1,%edx
  400779:       75 08                           jne    400783 <_Z4Mainv+0x163>
  40077b:       0f b6 94 04 00 01 00 00         movzbl 0x100(%rsp,%rax,1),%edx
  400783:       38 d1                           cmp    %dl,%cl
  400785:       0f 85 b2 00 00 00               jne    40083d <_Z4Mainv+0x21d>
  40078b:       48 83 c0 01                     add    $0x1,%rax
  40078f:       48 3d 00 01 00 00               cmp    $0x100,%rax
  400795:       75 d1                           jne    400768 <_Z4Mainv+0x148>
  400797:       c5 fd 6f 8c 24 00 02 00 00      vmovdqa 0x200(%rsp),%ymm1
  4007a0:       31 c0                           xor    %eax,%eax
  4007a2:       c4 e2 7d 17 c9                  vptest %ymm1,%ymm1
  4007a7:       0f 94 c0                        sete   %al
  4007aa:       0f 85 88 00 00 00               jne    400838 <_Z4Mainv+0x218>
  4007b0:       c5 fd 6f 8c 24 20 02 00 00      vmovdqa 0x220(%rsp),%ymm1
  4007b9:       31 c0                           xor    %eax,%eax
  4007bb:       c4 e2 7d 17 c9                  vptest %ymm1,%ymm1
  4007c0:       0f 94 c0                        sete   %al
  4007c3:       75 73                           jne    400838 <_Z4Mainv+0x218>
  4007c5:       c5 fd 6f 8c 24 40 02 00 00      vmovdqa 0x240(%rsp),%ymm1
  4007ce:       31 c0                           xor    %eax,%eax
  4007d0:       c4 e2 7d 17 c9                  vptest %ymm1,%ymm1
  4007d5:       0f 94 c0                        sete   %al
  4007d8:       75 5e                           jne    400838 <_Z4Mainv+0x218>
  4007da:       c5 fd 6f 8c 24 60 02 00 00      vmovdqa 0x260(%rsp),%ymm1
  4007e3:       31 c0                           xor    %eax,%eax
  4007e5:       c4 e2 7d 17 c9                  vptest %ymm1,%ymm1
  4007ea:       0f 94 c0                        sete   %al
  4007ed:       75 49                           jne    400838 <_Z4Mainv+0x218>
  4007ef:       c5 fd 6f 8c 24 80 02 00 00      vmovdqa 0x280(%rsp),%ymm1
  4007f8:       31 c0                           xor    %eax,%eax
  4007fa:       c4 e2 7d 17 c9                  vptest %ymm1,%ymm1
  4007ff:       0f 94 c0                        sete   %al
  400802:       75 34                           jne    400838 <_Z4Mainv+0x218>
  400804:       c5 fd 6f 8c 24 a0 02 00 00      vmovdqa 0x2a0(%rsp),%ymm1
  40080d:       31 c0                           xor    %eax,%eax
  40080f:       c4 e2 7d 17 c9                  vptest %ymm1,%ymm1
  400814:       0f 94 c0                        sete   %al
  400817:       75 1f                           jne    400838 <_Z4Mainv+0x218>
  400819:       c5 fd 6f 8c 24 c0 02 00 00      vmovdqa 0x2c0(%rsp),%ymm1
  400822:       31 c0                           xor    %eax,%eax
  400824:       c4 e2 7d 17 c9                  vptest %ymm1,%ymm1
  400829:       0f 94 c0                        sete   %al
  40082c:       75 0a                           jne    400838 <_Z4Mainv+0x218>
  40082e:       31 c0                           xor    %eax,%eax
  400830:       c4 e2 7d 17 c0                  vptest %ymm0,%ymm0
  400835:       0f 94 c0                        sete   %al
  400838:       c5 f8 77                        vzeroupper 
  40083b:       c9                              leaveq 
  40083c:       c3                              retq   
  40083d:       b9 20 09 40 00                  mov    $0x400920,%ecx
  400842:       ba 26 00 00 00                  mov    $0x26,%edx
  400847:       be e9 08 40 00                  mov    $0x4008e9,%esi
  40084c:       bf f8 08 40 00                  mov    $0x4008f8,%edi
  400851:       c5 f8 77                        vzeroupper 
  400854:       e8 97 fc ff ff                  callq  4004f0 <__assert_fail@plt>
  400859:       0f 1f 80 00 00 00 00            nopl   0x0(%rax)

GCC 5:

0000000000400630 <_Z4Mainv>:
  400630:       4c 8d 54 24 08                  lea    0x8(%rsp),%r10
  400635:       48 83 e4 e0                     and    $0xffffffffffffffe0,%rsp
  400639:       b8 20 00 00 00                  mov    $0x20,%eax
  40063e:       c5 f9 ef c0                     vpxor  %xmm0,%xmm0,%xmm0
  400642:       ba 25 08 40 00                  mov    $0x400825,%edx
  400647:       41 ff 72 f8                     pushq  -0x8(%r10)
  40064b:       55                              push   %rbp
  40064c:       48 89 e5                        mov    %rsp,%rbp
  40064f:       41 52                           push   %r10
  400651:       48 81 ec 08 03 00 00            sub    $0x308,%rsp
  400658:       c5 fd 7f 85 50 fd ff ff         vmovdqa %ymm0,-0x2b0(%rbp)
  400660:       c5 fd 7f 85 30 fd ff ff         vmovdqa %ymm0,-0x2d0(%rbp)
  400668:       c5 fd 7f 85 10 fd ff ff         vmovdqa %ymm0,-0x2f0(%rbp)
  400670:       c5 fd 7f 85 f0 fc ff ff         vmovdqa %ymm0,-0x310(%rbp)
  400678:       c5 fd 7f 85 d0 fd ff ff         vmovdqa %ymm0,-0x230(%rbp)
  400680:       c5 fd 7f 85 b0 fd ff ff         vmovdqa %ymm0,-0x250(%rbp)
  400688:       c5 fd 7f 85 90 fd ff ff         vmovdqa %ymm0,-0x270(%rbp)
  400690:       c5 fd 7f 85 70 fd ff ff         vmovdqa %ymm0,-0x290(%rbp)
  400698:       0f 1f 84 00 00 00 00 00         nopl   0x0(%rax,%rax,1)
  4006a0:       48 83 c2 01                     add    $0x1,%rdx
  4006a4:       c6 84 05 f0 fc ff ff 01         movb   $0x1,-0x310(%rbp,%rax,1)
  4006ac:       0f b6 42 ff                     movzbl -0x1(%rdx),%eax
  4006b0:       84 c0                           test   %al,%al
  4006b2:       75 ec                           jne    4006a0 <_Z4Mainv+0x70>
  4006b4:       c5 f9 ef c0                     vpxor  %xmm0,%xmm0,%xmm0
  4006b8:       31 c0                           xor    %eax,%eax
  4006ba:       c5 fd 7f 85 50 fe ff ff         vmovdqa %ymm0,-0x1b0(%rbp)
  4006c2:       c5 fd 7f 85 30 fe ff ff         vmovdqa %ymm0,-0x1d0(%rbp)
  4006ca:       c5 fd 7f 85 10 fe ff ff         vmovdqa %ymm0,-0x1f0(%rbp)
  4006d2:       c5 fd 7f 85 f0 fd ff ff         vmovdqa %ymm0,-0x210(%rbp)
  4006da:       c5 fd 7f 85 d0 fe ff ff         vmovdqa %ymm0,-0x130(%rbp)
  4006e2:       c5 fd 7f 85 b0 fe ff ff         vmovdqa %ymm0,-0x150(%rbp)
  4006ea:       c5 fd 7f 85 90 fe ff ff         vmovdqa %ymm0,-0x170(%rbp)
  4006f2:       c5 fd 7f 85 70 fe ff ff         vmovdqa %ymm0,-0x190(%rbp)
  4006fa:       c5 fd 7f 85 f0 fe ff ff         vmovdqa %ymm0,-0x110(%rbp)
  400702:       c5 fd 7f 85 10 ff ff ff         vmovdqa %ymm0,-0xf0(%rbp)
  40070a:       c5 fd 7f 85 30 ff ff ff         vmovdqa %ymm0,-0xd0(%rbp)
  400712:       c5 fd 7f 85 50 ff ff ff         vmovdqa %ymm0,-0xb0(%rbp)
  40071a:       c5 fd 7f 85 70 ff ff ff         vmovdqa %ymm0,-0x90(%rbp)
  400722:       c5 fd 7f 45 90                  vmovdqa %ymm0,-0x70(%rbp)
  400727:       c5 fd 7f 45 b0                  vmovdqa %ymm0,-0x50(%rbp)
  40072c:       c5 fd 7f 45 d0                  vmovdqa %ymm0,-0x30(%rbp)
  400731:       0f 1f 80 00 00 00 00            nopl   0x0(%rax)
  400738:       0f b6 94 05 f0 fc ff ff         movzbl -0x310(%rbp,%rax,1),%edx
  400740:       0f b6 8c 05 f0 fe ff ff         movzbl -0x110(%rbp,%rax,1),%ecx
  400748:       84 d2                           test   %dl,%dl
  40074a:       75 08                           jne    400754 <_Z4Mainv+0x124>
  40074c:       0f b6 94 05 f0 fd ff ff         movzbl -0x210(%rbp,%rax,1),%edx
  400754:       38 d1                           cmp    %dl,%cl
  400756:       75 2c                           jne    400784 <_Z4Mainv+0x154>
  400758:       48 83 c0 01                     add    $0x1,%rax
  40075c:       48 3d 00 01 00 00               cmp    $0x100,%rax
  400762:       75 d4                           jne    400738 <_Z4Mainv+0x108>
  400764:       c5 f9 ef c0                     vpxor  %xmm0,%xmm0,%xmm0
  400768:       31 c0                           xor    %eax,%eax
  40076a:       c4 e2 7d 17 c0                  vptest %ymm0,%ymm0
  40076f:       0f 94 c0                        sete   %al
  400772:       c5 f8 77                        vzeroupper 
  400775:       48 81 c4 08 03 00 00            add    $0x308,%rsp
  40077c:       41 5a                           pop    %r10
  40077e:       5d                              pop    %rbp
  40077f:       49 8d 62 f8                     lea    -0x8(%r10),%rsp
  400783:       c3                              retq   
  400784:       b9 60 08 40 00                  mov    $0x400860,%ecx
  400789:       ba 26 00 00 00                  mov    $0x26,%edx
  40078e:       be 29 08 40 00                  mov    $0x400829,%esi
  400793:       bf 38 08 40 00                  mov    $0x400838,%edi
  400798:       c5 f8 77                        vzeroupper 
  40079b:       e8 50 fd ff ff                  callq  4004f0 <__assert_fail@plt>

标签:c,gcc,avx2
来源: https://codeday.me/bug/20190724/1523324.html