It's analogous to if(0) the constant block is optimized to a do-block¹ ...

> perl -MO=Deparse -E'if (1) { label: say 1;}; goto label'
BEGIN {
    $^H{'feature_say'} = q(1);
    $^H{'feature_state'} = q(1);
    $^H{'feature_switch'} = q(1);
}
do {
    label: say 1
};
goto label;
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... which seems to fall into the same category like other loop-like-blocks:

ATM I have only 5.10 available. Could someone please test this with >= 5.12?

perl -wE'do { label: say 1;}; goto label'
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EDIT: removed exit

Update

here test code w/o endless looping.

perl -wE'my $x=0;do { label: say $x++; die if $x>1}; goto label'
0
1
Died at -e line 1.
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Update

Thanks to davido for testing

[davido]: LanX: perl -E 'goto IN; do{ IN: say "Hello world\n";};' does
+ produce the warning on 5.16.2.
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¹) which is somehow strange, I expected a simple bare block.