Revert "Perl_leave_adjust_stacks: don't make mortal copies of SvIMMORTAL SVs"

This reverts commit c56d7fa9134de66efe85a2fd70b28069c2629e0d.

Also un-TODO's the new test for this issue.

Fixes #21044

2 files changed, 0 insertions, 10 deletions

diff --git a/pp_hot.c b/pp_hot.c
index d9b4d6e6fb..3ec24a0e23 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -5085,13 +5085,6 @@ Perl_leave_adjust_stacks(pTHX_ SV **from_sp, SV **to_sp, U8 gimme, int pass)
                     }
                 }
             }
-            else if (SvIMMORTAL(sv)){
-                /* Since SvIMMORTALs are never freed, even when their
-                 * refcount drops to zero, there's no benefit in
-                 * creating a mortal copy.
-                 */
-                *++to_sp = sv;
-            }
             else {
                 /* Make a mortal copy of the SV.
                  * The following code is the equivalent of sv_mortalcopy()
diff --git a/t/op/sub.t b/t/op/sub.t
index 0eae1d50de..e703880ec8 100644
--- a/t/op/sub.t
+++ b/t/op/sub.t
@@ -445,8 +445,5 @@ fresh_perl_like(
 );
 
 # github #21044
-{
-    local $TODO = "sub return values not modifiable";
 ok( eval { $_->{x} = 1 for sub { undef }->(); 1 }, "check sub return values are modifiable")
   or diag $@;
-}