k0kubun	2017-05-26 21:12:13 +0900 (Fri, 26 May 2017)

  New Revision: 58904

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=58904

  Log:
    erb.rb: Use script encoding instead of force_encoding
    
    The original intention of introducing `_erbout.force_encoding`
    in r21170 was:
    
    - "returns a string in the same character encoding as the input string."
    - "When the input string has a magic comment, however, it returns a string
      in the encoding specified by the magic comment."
    
    And they are tested by test/erb/test_erb_m17n.rb well and this patch
    passes the test.
    Since magic comment is always added in ERB compiled code, using ''.dup
    instead of String.new will set correct encoding without calling
    force_encoding method.
    
    The benchmark results are:
    
    * Before
    
    $ ./ruby benchmark/run.rb --matzruby=./ruby -m bm_app_erb
    MatzRuby:
    ruby 2.5.0dev (2017-05-26 skip-force-enc.. 58903) [x86_64-linux]
    last_commit=Skip force_encoding in compiled code of erb
    Ruby:
    
    app_erb:
    matz 0.715
    
    * After
    
    $ ./ruby benchmark/run.rb --matzruby=./ruby -m bm_app_erb
    MatzRuby:
    ruby 2.5.0dev (2017-05-26 skip-force-enc.. 58903) [x86_64-linux]
    last_commit=Skip force_encoding in compiled code of erb
    Ruby:
    
    app_erb:
    matz 0.672
    
    And perf(1) results are:
    
    * Before
    
    $ sudo perf stat ./ruby benchmark/bm_app_erb.rb
    
     Performance counter stats for './ruby benchmark/bm_app_erb.rb':
    
            709.571746      task-clock (msec)         #    1.000 CPUs utilized
                     5      context-switches          #    0.007 K/sec
                     1      cpu-migrations            #    0.001 K/sec
                 1,337      page-faults               #    0.002 M/sec
         3,088,936,521      cycles                    #    4.353 GHz
       <not supported>      stalled-cycles-frontend
       <not supported>      stalled-cycles-backend
         4,849,564,282      instructions              #    1.57  insns per cycle
         1,027,042,087      branches                  # 1447.411 M/sec
            19,983,456      branch-misses             #    1.95% of all branches
    
           0.709747823 seconds time elapsed
    
    * After
    
    $ sudo perf stat ./ruby benchmark/bm_app_erb.rb
    
     Performance counter stats for './ruby benchmark/bm_app_erb.rb':
    
            693.494673      task-clock (msec)         #    1.000 CPUs utilized
                     7      context-switches          #    0.010 K/sec
                     1      cpu-migrations            #    0.001 K/sec
                 1,316      page-faults               #    0.002 M/sec
         3,025,639,349      cycles                    #    4.363 GHz
       <not supported>      stalled-cycles-frontend
       <not supported>      stalled-cycles-backend
         4,694,848,271      instructions              #    1.55  insns per cycle
           994,496,704      branches                  # 1434.037 M/sec
            19,693,239      branch-misses             #    1.98% of all branches
    
           0.693724345 seconds time elapsed
    
    [fix GH-1147]

  Modified files:
    trunk/lib/erb.rb
Index: lib/erb.rb
===================================================================
--- lib/erb.rb	(revision 58903)
+++ lib/erb.rb	(revision 58904)
@@ -280,7 +280,7 @@ class ERB https://github.com/ruby/ruby/blob/trunk/lib/erb.rb#L280
   # ERB#src:
   #
   #   compiler = ERB::Compiler.new('<>')
-  #   compiler.pre_cmd    = ["_erbout=String.new"]
+  #   compiler.pre_cmd    = ["_erbout=''.dup"]
   #   compiler.put_cmd    = "_erbout.<<"
   #   compiler.insert_cmd = "_erbout.<<"
   #   compiler.post_cmd   = ["_erbout"]
@@ -291,7 +291,7 @@ class ERB https://github.com/ruby/ruby/blob/trunk/lib/erb.rb#L291
   # <i>Generates</i>:
   #
   #   #coding:UTF-8
-  #   _erbout=String.new; _erbout.<< "Got "; _erbout.<<(( obj ).to_s); _erbout.<< "!\n"; _erbout
+  #   _erbout=''.dup; _erbout.<< "Got "; _erbout.<<(( obj ).to_s); _erbout.<< "!\n"; _erbout
   #
   # By default the output is sent to the print method.  For example:
   #
@@ -861,8 +861,8 @@ class ERB https://github.com/ruby/ruby/blob/trunk/lib/erb.rb#L861
   def set_eoutvar(compiler, eoutvar = '_erbout')
     compiler.put_cmd = "#{eoutvar}.<<"
     compiler.insert_cmd = "#{eoutvar}.<<"
-    compiler.pre_cmd = ["#{eoutvar} = String.new"]
-    compiler.post_cmd = ["#{eoutvar}.force_encoding(__ENCODING__)"]
+    compiler.pre_cmd = ["#{eoutvar} = ''.dup"]
+    compiler.post_cmd = [eoutvar]
   end
 
   # Generate results and print them. (see ERB#result)

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