[aarch64]std::is_permutation function Incorrect input parameter of the same value.

[dongjianqiang2]

demo.cpp

#include <algorithm>
#include <iostream>


int main (void) {
    bool rv=true;
    {
        std::initializer_list<int> a{1,2,3,4,5},b{5,4,3,2,1}, c{1,2,3,4};
        rv&=std::is_permutation(a.begin(), a.end(), b.begin());
        return std::is_permutation(a.begin(), a.end(), c.begin() );  //supposed to return 0;
    }
}

clang++ demo.cpp -O2
./a.out
echo $?
1

gdb ./a.out

0x0000aaaaaaaaa930 <+76>: ldr q0, [x10, #3520]
0x0000aaaaaaaaa934 <+80>: mov x1, x19
0x0000aaaaaaaaa938 <+84>: str w8, [sp, #32]
0x0000aaaaaaaaa93c <+88>: stp q0, q1, [sp]
0x0000aaaaaaaaa940 <+92>: bl 0xaaaaaaaaa968 <ZSt16__is_permutationIPKiS1_N9__gnu_cxx5__ops19_Iter_equal_to_iterEEbT_S5_T0_T1>
0x0000aaaaaaaaa944 <+96>: sub x0, x29, #0x20
0x0000aaaaaaaaa948 <+100>: mov x2, sp
0x0000aaaaaaaaa94c <+104>: mov x1, x19
=> 0x0000aaaaaaaaa950 <+108>: bl 0xaaaaaaaaa968 <ZSt16__is_permutationIPKiS1_N9__gnu_cxx5__ops19_Iter_equal_to_iterEEbT_S5_T0_T1>
0x0000aaaaaaaaa954 <+112>: and w0, w0, #0x1
0x0000aaaaaaaaa958 <+116>: ldp x29, x30, [sp, #80]
0x0000aaaaaaaaa95c <+120>: ldr x19, [sp, #96]
0x0000aaaaaaaaa960 <+124>: add sp, sp, #0x70
0x0000aaaaaaaaa964 <+128>: ret
End of assembler dump.
(gdb) x /5wx $x0
0xffffffffe940: 0x00000001 0x00000002 0x00000003 0x00000004
0xffffffffe950: 0x00000005
(gdb) x /5wx $x2
0xffffffffe910: 0x00000001 0x00000002 0x00000003 0x00000004
0xffffffffe920: 0x00000005

The same value is saved in the input space （x0 and x2)。
I look into the assemble and find that they may have used the same rodata.

[philnik777]

Your example has UB because the c range is smaller than the a range. If you want to check for ranges of different lenghts you can use std::is_permutation(a.begin(), a.end(), c.begin(), c.end()).