[Bug tree-optimization/102392] Failure to optimize a sign extension to a zero extension

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102392

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-09-18
             Status|UNCONFIRMED                 |NEW
          Component|target                      |tree-optimization
           Keywords|ABI                         |

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
A better testcase is:
void g(int32_t *x, int64_t *y)
{
    if (*x < 0)
        __builtin_unreachable();
    *y = (*x);
}

To see what LLVM is really doing.
GCC:
        movslq  (%rdi), %rax
        movq    %rax, (%rsi)
        ret

VS LLVM:
        movl    (%rdi), %eax
        movq    %rax, (%rsi)
        retq

There might be a dup of this bug somewhere too.