[Bug target/30315] optimize unsigned-add overflow test on x86 to use cpu flags from addl

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=30315

Vincent Lefèvre <vincent-gcc at vinc17 dot net> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vincent-gcc at vinc17 dot net

--- Comment #20 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
Similar to comment 16:

void d (unsigned int a, unsigned int b)
{
  unsigned int diff = a - b;
  if (diff == 0)
    feq ();
  else if (diff > a)
    flt ();
  else
    fgt ();
}

is not optimized.

Under Debian, GCC 10.0.0 20190527 (experimental) [trunk revision 271671] gives
for x86_64 (i386 is similar):

[...]
        xorl    %eax, %eax
        cmpl    %esi, %edi
        setb    %al
        je      .L7
        testl   %eax, %eax
        je      .L5
[...]

I would expect just a cmpl, a je and a jl.