Improve performance of implicit type conversion

To convert the object implicitly, it has had two parts in convert_type() which are
  1. lookink up the method's id
  2. calling the method

Seems that strncmp() and strcmp() in convert_type() are slightly heavy to look up
the method's id for type conversion.

This patch will add and use internal APIs (rb_convert_type_with_id, rb_check_convert_type_with_id)
to call the method without looking up the method's id when convert the object.

Array#flatten -> 19 % up
Array#+       ->  3 % up

[ruby-dev:50024] [Bug #13341] [Fix GH-1537]

### Before
       Array#flatten    104.119k (± 1.1%) i/s -    525.690k in   5.049517s
             Array#+      1.993M (± 1.8%) i/s -     10.010M in   5.024258s

### After
       Array#flatten    124.005k (± 1.0%) i/s -    624.240k in   5.034477s
             Array#+      2.058M (± 4.8%) i/s -     10.302M in   5.019328s

### Test Code
require 'benchmark/ips'

class Foo
  def to_ary
    [1,2,3]
  end
end

Benchmark.ips do |x|

  ary = []
  100.times { |i| ary << i }
  array = [ary]

  x.report "Array#flatten" do |i|
    i.times { array.flatten }
  end

  x.report "Array#+" do |i|
    obj = Foo.new
    i.times { array + obj }
  end

end

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58978 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 2 insertions, 2 deletions

diff --git a/string.c b/string.c
index 89e08d2cc2..df3f8fd3cd 100644
--- a/string.c
+++ b/string.c
@@ -1341,7 +1341,7 @@ rb_str_memsize(VALUE str)
 VALUE
 rb_str_to_str(VALUE str)
 {
-    return rb_convert_type(str, T_STRING, "String", "to_str");
+    return rb_convert_type_with_id(str, T_STRING, "String", idTo_str);
 }
 
 static inline void str_discard(VALUE str);
@@ -2225,7 +2225,7 @@ rb_str_fill_terminator(VALUE str, const int newminlen)
 VALUE
 rb_check_string_type(VALUE str)
 {
-    str = rb_check_convert_type(str, T_STRING, "String", "to_str");
+    str = rb_check_convert_type_with_id(str, T_STRING, "String", idTo_str);
     return str;
 }