Interesting, thanks for looking into it further!

I'm not sure what you mean about being able to return a value

I mean that in e.g. my $x = do { my $y = "foo" }, $x is assigned the return value of the assignment ("foo") - you can't do things like for example my $x = do { if (/x/) { "X" } else { "_" } } with a bare { BLOCK }.

This looks like an optimization issue, when do contains only a single statement, I guess it is optimized as a single statement executed in the containing scope

You may be onto something, there are some differences in the following two, although I don't know enough about the internals to say if the differences are relevant to the issue. I do think do { EXPR } shouldn't be optimized to just EXPR...

$ perl -MO=Concise -e 'sub DESTROY{print "Foo"} do{1;my $x=bless{}}; p
+rint "Bar"'
f  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 3 -e:1) v:{ ->3
-     <1> null vK*/1 ->b
a        <@> leave vKP ->b
3           <0> enter v ->4
-           <;> ex-nextstate(main 4 -e:1) v ->-
-           <0> ex-const v ->4
4           <;> nextstate(main 4 -e:1) v ->5
9           <2> sassign vKS/2 ->a
7              <@> bless sK/1 ->8
-                 <0> ex-pushmark s ->5
6                 <@> anonhash sK* ->7
5                    <0> pushmark s ->6
8              <0> padsv[$x:4,5] sRM*/LVINTRO ->9
b     <;> nextstate(main 6 -e:1) v:{ ->c
e     <@> print vK ->f
c        <0> pushmark s ->d
d        <$> const(PV "Bar") s ->e

$ perl -MO=Concise -e 'sub DESTROY{print "Foo"} do{  my $x=bless{}}; p
+rint "Bar"'
c  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 3 -e:1) v:{ ->3
-     <1> null vK*/1 ->8
-        <@> scope vK ->-
-           <;> ex-nextstate(main 4 -e:1) v ->-
7           <2> sassign vKS/2 ->8
5              <@> bless sK/1 ->6
-                 <0> ex-pushmark s ->3
4                 <@> anonhash sK* ->5
3                    <0> pushmark s ->4
6              <0> padsv[$x:4,5] sRM*/LVINTRO ->7
8     <;> nextstate(main 6 -e:1) v:{ ->9
b     <@> print vK ->c
9        <0> pushmark s ->a
a        <$> const(PV "Bar") s ->b
[download]

The fact that it works properly when the do contains more than one statement means there isn't a real problem though

It's still pretty inconsistent behavior IMO. Bug #133720 reported.

Update: Minor edits to wording.

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