compile.c: use rb_enc_interned_str to reduce allocations

The `rb_fstring(rb_enc_str_new())` pattern is inneficient because:

- It passes a mutable string to `rb_fstring` so if it has to be interned
  it will first be duped.
- It an equivalent interned string already exists, we allocated the string
  for nothing.

With `rb_enc_interned_str` we either directly get the pre-existing string
with 0 allocations, or efficiently directly intern the one we create
without first duping it.

1 files changed, 1 insertions, 1 deletions

diff --git a/test/ruby/test_shapes.rb b/test/ruby/test_shapes.rb
index bbea03344e..9b02504384 100644
--- a/test/ruby/test_shapes.rb
+++ b/test/ruby/test_shapes.rb
@@ -1006,7 +1006,7 @@ class TestShapes < Test::Unit::TestCase
   end
 
   def test_freezing_and_cloning_string
-    str = "str".freeze
+    str = ("str" + "str").freeze
     str2 = str.clone(freeze: true)
     assert_predicate(str2, :frozen?)
     assert_shape_equal(RubyVM::Shape.of(str), RubyVM::Shape.of(str2))