return early if there is no is_entries buffer

If there is a compilation error, is_entries may not be allocated, but
ic_size could be greater than 0.  If we don't have a buffer to iterate
over, just return early.  Otherwise GC could segv

[Bug #19173]

1 files changed, 7 insertions, 0 deletions

diff --git a/test/ruby/test_iseq.rb b/test/ruby/test_iseq.rb
index 2a18ff02e1..563aeeeaea 100644
--- a/test/ruby/test_iseq.rb
+++ b/test/ruby/test_iseq.rb
@@ -355,6 +355,13 @@ class TestISeq < Test::Unit::TestCase
     end
   end
 
+  # [Bug #19173]
+  def test_compile_error
+    assert_raise SyntaxError do
+      RubyVM::InstructionSequence.compile 'using Module.new; yield'
+    end
+  end
+
   def test_compile_file_error
     Tempfile.create(%w"test_iseq .rb") do |f|
       f.puts "end"