[Bug rtl-optimization/97387] New: we are near 2021, add carry intrinsic still does the wrong thing and generates silly code.

[euloanty at live dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97387

            Bug ID: 97387
           Summary: we are near 2021, add carry intrinsic still does the
                    wrong thing and generates silly code.
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: euloanty at live dot com
  Target Milestone: ---

#include <stdint.h>
#include <x86intrin.h>

void add256(uint64_t a[4], uint64_t b[4]){
  uint8_t carry = 0;
  for (int i = 0; i < 4; ++i)
    carry = _addcarry_u64(carry, a[i], b[i], &a[i]);
}

People have reported the issue for many many times but the carry is still
buggy.

https://gcc.godbolt.org/z/TnM8cv