Use <code> tags, otherwise array indices are turned into links.

#!/usr/bin/perl

use warnings; use strict; use Time::HiRes qw(gettimeofday tv_interval)
+; 


my( @suit, @deck); my @ups = qw( 0 0 0 0 0 0 0 0 0 0); my $cntr = 0; 

Deck();    # four shuffled suits are added to a deck and then shuffled

print "\n"; my $t0 = gettimeofday;

T0:    $ups[0] = Card(); $ups[1] = Card(); # draw cards for pos #0 & #
+1
T1:    if($ups[0] eq $ups[1]) { goto T0; }    # cover a pair & go back

    if($ups[2] eq '0') { $ups[2] = Card(); } # fill pos#2 if vacant

    # check pos#2 against pos#0 - cover a pair & go back
    if($ups[2] eq $ups[0]) { Cover(2,0); goto T1; }
    # check pos#2 against pos#1 - cover a pair & go back
      if($ups[2] eq $ups[1]) { Cover(2,1); goto T1; }

    # watch the rows for pairs that don't get covered
    foreach my $x (@ups) { print "$x "; } print "\n"; 

    for(my $j=3;$j<10;$j++) {
        if($ups[$j] eq '0') { $ups[$j] = Card(); }
        for(my $k=0;$k<$j;$k++) {
            if($ups[$j] eq $ups[$k]) { Cover($j,$k); goto T1; } } }   
+  

TX:    print "\n";
    foreach my $x (@ups) { print "$x "; } print "\t\tExit row\n"; 
    
    my $del_t = (gettimeofday - $t0) * 10**6;
    my $usec = sprintf("%.2f",$del_t);  
    print "\n$cntr passes in $usec microseconds. ";
    if($cntr == @deck) { print "Success!\n\n"; }
    else { print "{sigh...}\n\n"; }    

#========================================

sub Card {    my $tmp = $deck[$cntr]; $cntr++;
            if($tmp ne 'X') { return $tmp; } else { goto TX; } }

sub Suit {    @suit = qw(A B C D E F G H I J K L M ); 
            for(my $i=$#suit;$i>0;$i--) {
            my $j = int(rand($i + 1));
            @suit[$i, $j] = @suit[$j, $i]; } }    

sub Deck {    for(my $i=0;$i<4;$i++) { Suit(); @deck = (@deck,@suit); 
+}
            for(my $i=$#deck;$i>0;$i--) {
                my $j = int(rand($i + 1));
                @deck[$i, $j] = @deck[$j, $i];
            } push(@deck,"X"); }

sub Cover { my $x = $_[0]; my $y = $_[1];
            $ups[$x] = Card(); $ups[$y] = Card(); }
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I tried running the script 1000 times in 5.26.1 and the current blead (5.41.5-22-ga8a74a872d). There was no warning.