Optimize ruby visitor by Earlopain · Pull Request #3826 · ruby/prism

Earlopain · 2025-12-23T14:14:20Z

Looking at things like node.compact_child_nodes.each maybe we should have node.each_child_node? It would avoid the Array allocation and since there is no point to yield nil there is no need to name it node.each_compact_child_node.

This also came up someplace else before but I don't remember where. I agree this makes sense. cc @eregon

compact_child_nodes allocates an array. We can skip that step by simply yielding the nodes.

Benchmark for visiting the rails codebase:

require "prism"
require "benchmark/ips"

files = Dir.glob("../rails/**/*.rb")
results = files.map { Prism.parse_file(it) }
visitor = Prism::Visitor.new

Benchmark.ips do |x|
  x.config(warmup: 3, time: 10)

  x.report do
    results.each do
      visitor.visit(it.value)
    end
  end
end

RubyVM::YJIT.enable

Benchmark.ips do |x|
  x.config(warmup: 3, time: 10)

  x.report do
    results.each do
      visitor.visit(it.value)
    end
  end
end

Before:

ruby 3.4.8 (2025-12-17 revision 995b59f666) +PRISM [x86_64-linux]
Warming up --------------------------------------
                         1.000 i/100ms
Calculating -------------------------------------
                          2.691 (± 0.0%) i/s  (371.55 ms/i) -     27.000 in  10.089422s
ruby 3.4.8 (2025-12-17 revision 995b59f666) +YJIT +PRISM [x86_64-linux]
Warming up --------------------------------------
                         1.000 i/100ms
Calculating -------------------------------------
                          7.278 (±13.7%) i/s  (137.39 ms/i) -     70.000 in  10.071568s

After:

ruby 3.4.8 (2025-12-17 revision 995b59f666) +PRISM [x86_64-linux]
Warming up --------------------------------------
                         1.000 i/100ms
Calculating -------------------------------------
                          3.429 (± 0.0%) i/s  (291.65 ms/i) -     35.000 in  10.208580s
ruby 3.4.8 (2025-12-17 revision 995b59f666) +YJIT +PRISM [x86_64-linux]
Warming up --------------------------------------
                         1.000 i/100ms
Calculating -------------------------------------
                         16.815 (± 0.0%) i/s   (59.47 ms/i) -    169.000 in  10.054668s

~21% faster on the interpreter, ~56% with YJIT

`compact_child_nodes` allocates an array. We can skip that step by simply yielding the nodes. Benchmark for visiting the rails codebase: ```rb require "prism" require "benchmark/ips" files = Dir.glob("../rails/**/*.rb") results = files.map { Prism.parse_file(it) } visitor = Prism::Visitor.new Benchmark.ips do |x| x.config(warmup: 3, time: 10) x.report do results.each do visitor.visit(it.value) end end end RubyVM::YJIT.enable Benchmark.ips do |x| x.config(warmup: 3, time: 10) x.report do results.each do visitor.visit(it.value) end end end ``` Before: ``` ruby 3.4.8 (2025-12-17 revision 995b59f666) +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 2.691 (± 0.0%) i/s (371.55 ms/i) - 27.000 in 10.089422s ruby 3.4.8 (2025-12-17 revision 995b59f666) +YJIT +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 7.278 (±13.7%) i/s (137.39 ms/i) - 70.000 in 10.071568s ``` After: ``` ruby 3.4.8 (2025-12-17 revision 995b59f666) +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 3.429 (± 0.0%) i/s (291.65 ms/i) - 35.000 in 10.208580s ruby 3.4.8 (2025-12-17 revision 995b59f666) +YJIT +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 16.815 (± 0.0%) i/s (59.47 ms/i) - 169.000 in 10.054668s ``` ~21% faster on the interpreter, ~56% with YJIT

Earlopain · 2025-12-23T14:14:57Z

templates/sig/prism/node.rbs.erb

    def child_nodes: () -> Array[Prism::node?]
    def comment_targets: () -> Array[Prism::node | Location]
    def compact_child_nodes: () -> Array[Prism::node]
+    def each_child_node: () { (Prism::node) -> void } -> void | () -> Enumerator[Prism::node]


Unsure if this is correct. I'm also missing sorbet signatures which I don't know how to write for this

This looks right to me, and it would have failed to typecheck otherwise.

So are sorbet signatures not needed? I don't use these systems so no idea when/where it gets used. Other functions are present so I assume there is a reason for them.

Earlopain · 2025-12-23T14:15:38Z

templates/lib/prism/node.rb.erb

+    end
+
    # def compact_child_nodes: () -> Array[Node]
    def compact_child_nodes


This can just be implemented as each_child_node.to_a but performance is not so great

Nope, you're right to keep this the same.

eregon · 2025-12-30T10:33:38Z

Nice, thank you!
Probably I should revisit https://eregon.me/blog/2024/10/27/benchmarking-ruby-parsers.html with this, Prism would be even faster for Parsing and Walking :)

FWIW in the description you mention

~21% faster on the interpreter, ~56% with YJIT

but the numbers above look much better than that to me, I would say 16.815/7.278 = 2.3x "as fast" / 130% "faster" (and I think "2.3x faster" is clear for most people too).
I guess you counted as 1 - 7.278/16.815 = 56% "less time", which is correct too but maybe confusing together with "faster"?
I'm not sure if there is standard for this 😅
FWIW Benchmark.ips compare! uses "2x faster":

$ ruby -rbenchmark/ips -e 'Benchmark.ips { it.report(:a) { sleep 0.2 }; it.report(:b) { sleep 0.1 }; it.compare!(order: :baseline) }'
ruby 3.4.7 (2025-10-08 revision 7a5688e2a2) +PRISM [x86_64-linux]
Warming up --------------------------------------
                   a     1.000 i/100ms
                   b     1.000 i/100ms
Calculating -------------------------------------
                   a      4.998 (± 0.0%) i/s  (200.08 ms/i) -     25.000 in   5.002088s
                   b      9.984 (± 0.0%) i/s  (100.16 ms/i) -     50.000 in   5.008167s

Comparison:
a:        5.0 i/s
b:       10.0 i/s - 2.00x  faster

eregon · 2025-12-30T10:37:55Z

templates/lib/prism/node.rb.erb

+      <%- when Prism::Template::OptionalNodeField -%>
+      yield <%= field.name %> if <%= field.name %>
+      <%- when Prism::Template::NodeListField -%>
+      <%= field.name %>.each  {|node| yield node }


Suggested change

<%= field.name %>.each {|node| yield node }

<%= field.name %>.each(&block)

might be faster because it avoids an extra block (that literal block) and consumes less stack (both good for performance and to avoid stack overflow errors).
I'll give it a try.

I tried

diff --git i/templates/lib/prism/node.rb.erb w/templates/lib/prism/node.rb.erb index c97c029d3..76cbb2608 100644 --- i/templates/lib/prism/node.rb.erb +++ w/templates/lib/prism/node.rb.erb @@ -343,8 +343,8 @@ module Prism end # def each_child_node: () { (Prism::node) -> void } -> void | () -> Enumerator[Prism::node] - def each_child_node - return to_enum(:each_child_node) unless block_given? + def each_child_node(&_block) + return to_enum(:each_child_node) unless _block <%- node.fields.each do |field| -%> <%- case field -%> @@ -353,7 +353,7 @@ module Prism <%- when Prism::Template::OptionalNodeField -%> yield <%= field.name %> if <%= field.name %> <%- when Prism::Template::NodeListField -%> - <%= field.name %>.each {|node| yield node } + <%= field.name %>.each(&_block) <%- end -%> <%- end -%> end

and it seems a little bit faster in interpreter but much slower in YJIT (2 runs each to get an idea of variance, for some reason the ± 0.0% seems broken in benchmark-ips):

BEFORE: $ ruby -Ilib bench_visitor.rb ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 2.720 (± 0.0%) i/s (367.65 ms/i) - 28.000 in 10.294286s ruby 4.0.0 (2025-12-25 revision 553f1675f3) +YJIT +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 14.286 (± 0.0%) i/s (70.00 ms/i) - 143.000 in 10.009988s $ ruby -Ilib bench_visitor.rb ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 2.740 (± 0.0%) i/s (364.94 ms/i) - 28.000 in 10.218390s ruby 4.0.0 (2025-12-25 revision 553f1675f3) +YJIT +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 14.309 (± 0.0%) i/s (69.88 ms/i) - 144.000 in 10.064832s AFTER: $ ruby -Ilib bench_visitor.rb ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 2.790 (± 0.0%) i/s (358.37 ms/i) - 28.000 in 10.034481s ruby 4.0.0 (2025-12-25 revision 553f1675f3) +YJIT +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 11.968 (± 0.0%) i/s (83.55 ms/i) - 120.000 in 10.026674s $ ruby -Ilib bench_visitor.rb ruby 4.0.0 (2025-12-25 revision 553f1675f3) +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 2.805 (± 0.0%) i/s (356.53 ms/i) - 29.000 in 10.339397s ruby 4.0.0 (2025-12-25 revision 553f1675f3) +YJIT +PRISM [x86_64-linux] Warming up -------------------------------------- 1.000 i/100ms Calculating ------------------------------------- 12.116 (± 0.0%) i/s (82.54 ms/i) - 122.000 in 10.069442s

Earlopain · 2025-12-31T11:24:27Z

but the numbers above look much better than that to me

Yeah, I could have written that more clearly. benchmark/ips has https://github.com/evanphx/benchmark-ips?tab=readme-ov-file#independent-benchmarking but I was too lazy

Earlopain commented Dec 23, 2025

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kddnewton approved these changes Dec 29, 2025

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kddnewton merged commit 4f86847 into ruby:main Dec 29, 2025
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eregon reviewed Dec 30, 2025

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Optimize ruby visitor#3826

Optimize ruby visitor#3826
kddnewton merged 1 commit intoruby:mainfrom
Earlopain:optimize-ruby-visitor

Earlopain commented Dec 23, 2025

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	<%= field.name %>.each {\|node\| yield node }
	<%= field.name %>.each(&block)

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