Issue #9382 has been reported by tmm1 (Aman Gupta).

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Bug #9382: [patch] add opt_aref_str and opt_aset_str
https://bugs.ruby-lang.org/issues/9382

Author: tmm1 (Aman Gupta)
Status: Open
Priority: Normal
Assignee: tmm1 (Aman Gupta)
Category: 
Target version: current: 2.2.0
ruby -v: trunk
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN, 2.1: UNKNOWN


@charliesome, @normalperson and I have been working on a patch to add two new instructions:

  https://bugs.ruby-lang.org/issues/9188#note-9

These optimize Hash#[] and Hash#[]=, when used with a string literal key.

Before:

  0010 putstring        "str"
  0012 opt_aref         <callinfo!mid:[], argc:1, ARGS_SKIP>

After:

  0010 opt_aref_str     <callinfo!mid:[], argc:1, ARGS_SKIP>, "str"

The opt_(aref|aset)_str instructions avoid str_duplicate, resulting in reduced allocation overhead. For example, this loop requires zero allocations after the patch:

  hash={}; loop{ hash["key"] += 1 }

In our rails app, 2.5% of iseqs can benefit from these optimizations:

  $ ruby -rconfig/environment -e' p ObjectSpace.each_object(RubyVM::InstructionSequence).count '
  63314

  $ ruby -rconfig/environment -e' p ObjectSpace.each_object(RubyVM::InstructionSequence).select{ |i| i.disasm.match(/ opt_(aref|aset)_str /) }.size '
  1464

@headius is also adding a similar optimization to jruby: https://bugs.ruby-lang.org/issues/8998#note-15

I plan to commit the patch above, so if you have any feedback on the implementation please share.


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