[Bug target/115995] RISC-V: Can't generate portable RVV code for rv64gcv_zvl512b

[sh.chiang04 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115995

--- Comment #1 from Monk Chiang <sh.chiang04 at gmail dot com> ---
Another test, the compile option is "g++ -march=rv64gcv_zvl128b -mabi=lp64d
-O3"

#include <numeric>
#include <vector>
#include <iterator>

using namespace std;

int main ()
{
 std::vector<int> data = {2, 2, 2, 2, 2, 2};
 std::vector<int> result (6, int(-1));

 std::vector<int>::iterator start = data.begin();
 std::vector<int>::iterator end = data.end();
 std::vector<int>::iterator result_start = result.begin();
 std::adjacent_difference(start, end, result_start);

 if (result[4] == 0)
   exit (0);
 else
   abort ();
}

After do adjacent_difference the result[] value should be [2, 0, 0, 0, 0, 0]