Fix bad write in pp_trans

y/// has not been extending the stack for lexical $_, even since lex-
ical $_ was added.  $lexical =~ y/// has not been extending the stack
since v5.21.5-339-g05a502d.

2 files changed, 9 insertions, 3 deletions

diff --git a/pp.c b/pp.c
index 0e011b6446..671bb9b815 100644
--- a/pp.c
+++ b/pp.c
@@ -746,11 +746,13 @@ PP(pp_trans)
 
     if (PL_op->op_flags & OPf_STACKED)
 	sv = POPs;
-    else if (ARGTARG)
-	sv = GETTARGET;
     else {
-	sv = DEFSV;
 	EXTEND(SP,1);
+	if (ARGTARG)
+	    sv = GETTARGET;
+	else {
+	    sv = DEFSV;
+	}
     }
     if(PL_op->op_type == OP_TRANSR) {
 	STRLEN len;
diff --git a/t/op/tr.t b/t/op/tr.t
index 8a7dd8aafe..c45971a382 100644
--- a/t/op/tr.t
+++ b/t/op/tr.t
@@ -10,6 +10,10 @@ BEGIN {
 
 plan tests => 134;
 
+# Test this first before we extend the stack with other operations.
+# This caused an asan failure due to a bad write past the end of the stack.
+eval { my $x; die  1..127, $x =~ y/// };
+
 my $Is_EBCDIC = (ord('i') == 0x89 & ord('J') == 0xd1);
 
 $_ = "abcdefghijklmnopqrstuvwxyz";