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Add Performance::NumericPredicate cop #440

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@miry miry commented Feb 6, 2024

Performance::NumericPredicate cop identifies places where numeric uses predicates like positive?, negative? and for some cases zero? should be converted to compare operator.

The Performance::NumericPredicate cop is added to identify instances where numeric predicates such as positive?, negative?, and occasionally zero? should be replaced with comparison operators for improved efficiency.

Predicates incur a performance overhead by executing a method before comparison. A small benchmark comparison between using a comparison operator (> 0) and positive? illustrates the performance difference:

x.report("compare with 0") { arr.each {|i| i > 0 } }
x.report("positive?") { arr.each {|i| i.positive? } }

Benchmark results on Ruby 3.3.0 (with YJIT) indicate a significant performance gain when using the comparison operator:

ruby 3.3.0 (2023-12-25 revision 5124f9ac75) +YJIT [arm64-darwin23]
Warming up --------------------------------------
      compare with 0     1.000 i/100ms
           positive?     1.000 i/100ms
Calculating -------------------------------------
      compare with 0      3.153 (± 0.0%) i/s -     95.000 in  30.132600s
           positive?      2.397 (± 0.0%) i/s -     72.000 in  30.042688s

Comparison:
      compare with 0:        3.2 i/s
           positive?:        2.4 i/s - 1.32x  slower

This cop is unsafe because it cannot be guaranteed that the receiver is Number and could be noisy.


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  • Added tests.
  • Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
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Performance::NumericPredicate cop identifies places where numeric uses predicates like
`positive?`, `negative?` and for some cases `zero?` should be converted to compare operator.

The `Performance::NumericPredicate` cop is added to identify instances where numeric predicates
such as `positive?`, `negative?`, and occasionally `zero?` should be replaced
with comparison operators for improved efficiency.

Predicates incur a performance overhead by executing a method before comparison.
A small benchmark comparison between using a comparison operator (`> 0`) and `positive?` illustrates the performance difference:

```ruby
x.report("compare with 0") { arr.each {|i| i > 0 } }
x.report("positive?") { arr.each {|i| i.positive? } }
```

Benchmark results on Ruby 3.3.0 (with YJIT) indicate a significant performance gain when using the comparison operator:

```
ruby 3.3.0 (2023-12-25 revision 5124f9ac75) +YJIT [arm64-darwin23]
Warming up --------------------------------------
      compare with 0     1.000 i/100ms
           positive?     1.000 i/100ms
Calculating -------------------------------------
      compare with 0      3.153 (± 0.0%) i/s -     95.000 in  30.132600s
           positive?      2.397 (± 0.0%) i/s -     72.000 in  30.042688s

Comparison:
      compare with 0:        3.2 i/s
           positive?:        2.4 i/s - 1.32x  slower
```

This cop is unsafe because it cannot be guaranteed that the receiver is Number and could be noisy.

Signed-off-by: Michael Nikitochkin <[email protected]>
REPLACEMENTS = { negative?: '<', positive?: '>', zero?: '==' }.freeze

def_node_matcher :num_predicate?, <<~PATTERN
(send $numeric_type? ${:negative? :positive? :zero?})
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Should this also look for nonzero?

@Earlopain
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This is just Style/NumericPredicate, is it not? It's configured for predicates by default so it would say that they will flip-flop between each other if not handled specifically. I'm also not sure if its worth the effort to duplicate a cop for what should basically be a different config value.

@miry
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miry commented Sep 14, 2024

@Earlopain Are there any established practices for handling conflicts between rubocop cops and performance cops?
I wonder, if there is a way to check the RuboCop configuration to ensure that the performance-related cops are enabled.

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3 participants