i386: Implement .SAT_ADD for unsigned scalar integers [PR112600]

The following testcase:

unsigned
add_sat(unsigned x, unsigned y)
{
    unsigned z;
    return __builtin_add_overflow(x, y, &z) ? -1u : z;
}

currently compiles (-O2) to:

add_sat:
        addl    %esi, %edi
        jc      .L3
        movl    %edi, %eax
        ret
.L3:
        orl     $-1, %eax
        ret

We can expand through usadd{m}3 optab to use carry flag from the addition
and generate branchless code using SBB instruction implementing:

    unsigned res = x + y;
    res |= -(res < x);

add_sat:
        addl    %esi, %edi
        sbbl    %eax, %eax
        orl     %edi, %eax
        ret

	PR target/112600

gcc/ChangeLog:

	* config/i386/i386.md (usadd<mode>3): New expander.
	(x86_mov<mode>cc_0_m1_neg): Use SWI mode iterator.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr112600-a.c: New test.

0 files changed, 0 insertions, 0 deletions