[Bug inline-asm/82701] RFE: x86: double word operands in inline assembly

[hpa at zytor dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82701

--- Comment #1 from H. Peter Anvin <hpa at zytor dot com> ---
I just stumbled onto this technique somewhat by accident:

union dw {
    uint64_t q;
    uint32_t l[2];
};

union dw aa, bb;

aa.q = a;
bb.q = b;

asm("add %2,%0; adc %3,%1"