Assuming you're discussing (($x1 eq $y1) and ($x2 eq $y2)) vs. ($x1 eq $y1 && $x2 eq $y2)

Since, they deparse to the same thing, how can one be a "failure"? Are you claiming that they do different things, or that one is harder to understand and maintain?

% perl -MO=Deparse -e'if($x1 eq $y1 && $x2 eq $y2){}'
if ($x1 eq $y1 and $x2 eq $y2) {
    ();
}

% perl -MO=Deparse -e'if(($x1 eq $y1) and ($x2 eq $y2)){}'
if ($x1 eq $y1 and $x2 eq $y2) {
    ();
}
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-Blake