if:    ($var eq "A" || $var eq 'B' || $var eq 'C')
ihash: { A=>1, B=>1, C=>1 }->{$var}
shash: $hash{$var}
re:    $var =~ /^(?:A|B|C)\z/

Benchmarking no matches

           Rate ihash    re    if shash
ihash  328339/s    --  -79%  -81%  -86%
re    1557274/s  374%    --  -10%  -33%
if    1738308/s  429%   12%    --  -25%
shash 2307394/s  603%   48%   33%    --

Benchmarking match A

           Rate ihash    re shash    if
ihash  333900/s    --  -78%  -83%  -88%
re    1532032/s  359%    --  -21%  -43%
shash 1946689/s  483%   27%    --  -28%
if    2707780/s  711%   77%   39%    --

Benchmarking match B

           Rate ihash    re shash    if
ihash  324969/s    --  -78%  -84%  -84%
re    1473476/s  353%    --  -26%  -28%
shash 2004671/s  517%   36%    --   -2%
if    2053900/s  532%   39%    2%    --

Benchmarking match C

           Rate ihash    re    if shash
ihash  335514/s    --  -76%  -81%  -83%
re    1392243/s  315%    --  -20%  -28%
if    1744756/s  420%   25%    --   -9%
shash 1920959/s  473%   38%   10%    --