[ruby-core:83000] [Ruby trunk Feature#13602][Rejected] Optimize instance variable access if $VERBOSE is not true when compiling

Issue #13602 has been updated by jeremyevans0 (Jeremy Evans).

Status changed from Feedback to Rejected

ko1 (Koichi Sasada) wrote:
> It seems 5% can not justify this kind of optimization.
> 
> We can use your technique when we revert all of optimized instructions when $VERBOSE was changed. But I'm not sure this kind of modification is valuable than implementation cost (it can be).

I think this can be rejected then.  Reverting the optimized instructions would require compiling both the unoptimized version and the optimized version and keeping both in memory, or recompiling on a change to $VERBOSE, neither of which seems like a reasonable approach considering the modest performance improvement.

----------------------------------------
Feature #13602: Optimize instance variable access if $VERBOSE is not true when compiling
https://bugs.ruby-lang.org/issues/13602#change-66910

* Author: jeremyevans0 (Jeremy Evans)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
This patch optimizes instance variable lookup in the case the $VERBOSE
is not true when compiling.  If $VERBOSE is not true when compiling
code, it makes the instance variable access use an optimized VM
instruction that does not check $VERBOSE at runtime.

This does not change the behavior if $VERBOSE is not changed at runtime,
only when $VERBOSE is not true when compiling the code, but is true when
running it.  In the case where $VERBOSE is not true when compiling and
true at runtime, this patch makes ruby no longer emit the warning
message.

Using a similar benchmark as #10396:

~~~
require 'benchmark/ips'

class A
  def initialize
    @c = @d = @e = @f = nil
  end
  def b
    @c || @d || @e || @f
  end
end

Benchmark.ips do |x|
  x.report("A.new.b"){A.new.b}
  x.report("A.allocate.b"){A.allocate.b}
end
~~~

Before Patch:

~~~
             A.new.b    347.380k (_ 1.7%) i/s -      1.741M
        A.allocate.b    862.884k (_ 0.4%) i/s -      4.317M

             A.new.b    338.830k (_ 1.7%) i/s -      1.706M
        A.allocate.b    848.036k (_ 0.4%) i/s -      4.254M

             A.new.b    344.167k (_ 1.7%) i/s -      1.731M
        A.allocate.b    826.183k (_ 0.4%) i/s -      4.138M
~~~

After Patch:

~~~
             A.new.b    350.251k (_ 1.7%) i/s -      1.753M
        A.allocate.b    900.666k (_ 0.7%) i/s -      4.512M

             A.new.b    349.868k (_ 1.7%) i/s -      1.760M
        A.allocate.b    898.292k (_ 0.4%) i/s -      4.505M

             A.new.b    349.690k (_ 1.7%) i/s -      1.751M
        A.allocate.b    888.524k (_ 0.6%) i/s -      4.444M
~~~

So about a 1-2% increase in the case where instance variables are
already initialized, and about 5-7% increase in the case where
instance variables are not initialized. 

---Files--------------------------------
0001-Optimize-instance-variable-access-if-VERBOSE-is-not-.patch (4.88 KB)


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