If we are using too many conditional IF, ELSEIF or ELSE statements it will impact performance. We can think of using a switch statement instead of multiple if-else if possible, or refactor code to reduce number of IF, ELSEIF and ELSE statements. Sometimes called "complexity cyclomatic". Switch statement has a performance advantage over if – else.

Functional rules

one variable must be used maximum twice in IF / ELSEIF / ELSE statements at the same level - WARNINGs :
IF and ELSEIF statements use explicitly variable names !
ELSE statements use implicity variable names !
one variable must be used maximum twice in IF / ELSEIF / ELSE statements at differents hierarchical levels
we can assume that if one variable is used three times or more, we should :
use a SWITCH statement instead
or refactor the code if possible

Non compliant Code Example

NON compliant, because $nb is used 4 times : - 2 explicit times in IF statements - 2 implicit times in ELSE statements

$index = 1;
$nb = 2;
...
if ($nb == 0) {
    $nb = $index;
} elseif ($nb == 1) {
    $nb = $index * 2;
} elseif ($nb == 2) {
    $nb = $index * 3;
} else {
    $nb = -1;
}
return $nb;

Compliant Code Example

SWITCH statement solution + refactor solution

$index = 1;
$nb = 2;
...
switch ($nb) {
    case 0:
    case 1:
    case 2:
        $nb = $index * ($nb + 1);
        break;
    default:
        $nb = -1;
}
return $nb;