From e1548254d1365ef0342d5b64bb1fd1d996c1f70f Mon Sep 17 00:00:00 2001
From: Rafael Garcia-Suarez <rgarciasuarez@gmail.com>
Date: Tue, 24 Feb 2004 22:34:06 +0000
Subject: [PATCH] Fix a segfault during optree construction. (bug #27024)

p4raw-id: //depot/perl@22371
---
 op.c            |  4 ++++
 t/comp/parser.t | 10 +++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/op.c b/op.c
index c5b2e83..4bd252c 100644
--- a/op.c
+++ b/op.c
@@ -3577,6 +3577,10 @@ Perl_newLOOPOP(pTHX_ I32 flags, I32 debuggable, OP *expr, OP *block)
 	}
     }
 
+    /* if block is null, the next append_elem() would put UNSTACK, a scalar
+     * op, in listop. This is wrong. [perl #27024] */
+    if (!block)
+	block = newOP(OP_NULL, 0);
     listop = append_elem(OP_LINESEQ, block, newOP(OP_UNSTACK, 0));
     o = new_logop(OP_AND, 0, &expr, &listop);
 
diff --git a/t/comp/parser.t b/t/comp/parser.t
index e59fec6..2c25807 100644
--- a/t/comp/parser.t
+++ b/t/comp/parser.t
@@ -9,7 +9,7 @@ BEGIN {
 }
 
 require "./test.pl";
-plan( tests => 43 );
+plan( tests => 44 );
 
 eval '%@x=0;';
 like( $@, qr/^Can't modify hash dereference in repeat \(x\)/, '%@x=0' );
@@ -147,3 +147,11 @@ EOF
     eval q{ sub f { @a=@b=@c;  {use} } };
     like( $@, qr/syntax error/, "use without body" );
 }
+
+# Bug #27024
+{
+    # this used to segfault (because $[=1 is optimized away to a null block)
+    my $x;
+    $[ = 1 while $x;
+    pass();
+}
-- 
2.7.4