Issue #11786 has been reported by Eric Wong.

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Feature #11786: [PATCH] micro-optimize case dispatch even harder
https://bugs.ruby-lang.org/issues/11786

* Author: Eric Wong
* Status: Open
* Priority: Normal
* Assignee: 
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I noticed these optimizations while working on r52931.

By using a bare hash table, we avoid the overhead of rb_hash_*
functions as well as the cost of translating FIX2INT for jump
labels.

This also reduces GC overhead, as the iseq mark array no longer
carries redundant objects nor the Hash object.

Summary speedup:

loop_whileloop2	1.000
vm2_case*	1.225
vm2_case_lit*	1.000
vm2_case_small*	1.162

Passes all tests and specs, so probably safe to commit soon...

Full results:

2015-12-08 03:26:19 +0000
target 0: a (ruby 2.3.0dev (2015-12-08 trunk 52932) [x86_64-linux]) at "/home/ew/rrrr/b/ruby"
target 1: b (ruby 2.3.0dev (2015-12-08 master 52932) [x86_64-linux]
last_commit=micro-optimize case dispatch even harder) at "/home/ew/ruby/b/ruby"

-----------------------------------------------------------
loop_whileloop2

i = 0
while i< 6_000_000 # benchmark loop 2
  i += 1
end

a	0.10256672604009509
a	0.10279557690955698
a	0.10286601004190743
a	0.10278227413073182
a	0.10278794192709029
b	0.10288732498884201
b	0.10327051300555468
b	0.1026718900538981
b	0.10263488302007318
b	0.10256404406391084

-----------------------------------------------------------
vm2_case

i = 0
while i<6_000_000 # while loop 2
  case :foo
  when :bar
    raise
  when :baz
    raise
  when :boo
    raise
  when :foo
    i += 1
  end
end

a	0.18099936190992594
a	0.1836838680319488
a	0.1825075231026858
a	0.18087006197310984
a	0.18375545786693692
b	0.16652655508369207
b	0.16673082998022437
b	0.16754083498381078
b	0.16704767406918108
b	0.16648077592253685

-----------------------------------------------------------
vm2_case_lit

i = 0
@ret = [ "foo", true, false, :sym, 6, nil, 0.1, 0xffffffffffffffff ]
def foo(i)
  @ret[i % @ret.size]
end

while i<6_000_000 # while loop 2
  case foo(i)
  when "foo" then :foo
  when true then true
  when false then false
  when :sym then :sym
  when 6 then :fix
  when nil then nil
  when 0.1 then :float
  when 0xffffffffffffffff then :big
  end
  i += 1
end

a	0.670805990928784
a	0.6559841448906809
a	0.6560367799829692
a	0.655022048857063
a	0.671947613125667
b	0.659776204964146
b	0.6549702121410519
b	0.6788892599288374
b	0.6793588208965957
b	0.6878500080201775

-----------------------------------------------------------
vm2_case_small

i = 0
while i<6_000_000 # while loop 2
  case :foo
  when :foo
    i += 1
  else
    raise
  end
end

a	0.1667630800511688
a	0.16669297800399363
a	0.1665362489875406
a	0.16644068900495768
a	0.16646360605955124
b	0.15790433110669255
b	0.15774213010445237
b	0.15753646893426776
b	0.15781028987839818
b	0.15771835204213858

Elapsed time: 11.069307098 (sec)
-----------------------------------------------------------
benchmark results:
minimum results in each 5 measurements.
Execution time (sec)
name	a	b
loop_whileloop2	0.103	0.103
vm2_case*	0.078	0.064
vm2_case_lit*	0.552	0.552
vm2_case_small*	0.064	0.055


---Files--------------------------------
0001-micro-optimize-case-dispatch-even-harder.patch (9.34 KB)


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