From 5264d2fc4c741879ed918e06a9b10c74097ac2a9 Mon Sep 17 00:00:00 2001
From: Andrew Konchin <andrii.konchyn@oracle.com>
Date: Wed, 18 Jan 2023 16:46:42 +0200
Subject: [PATCH] Improve performance of Array#& by choosing the smallest of 2
 arrays to create a Hash

---
 spec/ruby/core/array/intersect_spec.rb      |  2 ++
 spec/ruby/core/array/shared/intersection.rb | 11 +++++++----
 src/main/ruby/truffleruby/core/array.rb     | 11 ++++++++---
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/spec/ruby/core/array/intersect_spec.rb b/spec/ruby/core/array/intersect_spec.rb
index 773e44c0734c..d415069dcfc0 100644
--- a/spec/ruby/core/array/intersect_spec.rb
+++ b/spec/ruby/core/array/intersect_spec.rb
@@ -13,6 +13,8 @@
       it 'returns false' do
         [0, 1, 2].intersect?([3, 4]).should == false
         [3, 4].intersect?([0, 1, 2]).should == false
+        [3, 4].intersect?([]).should == false
+        [].intersect?([0, 1, 2]).should == false
       end
     end
   end
diff --git a/spec/ruby/core/array/shared/intersection.rb b/spec/ruby/core/array/shared/intersection.rb
index 49849b08c231..64e143ad0da5 100644
--- a/spec/ruby/core/array/shared/intersection.rb
+++ b/spec/ruby/core/array/shared/intersection.rb
@@ -48,17 +48,20 @@
     obj2 = mock('2')
     obj1.stub!(:hash).and_return(0)
     obj2.stub!(:hash).and_return(0)
-    obj1.should_receive(:eql?).at_least(1).and_return(true)
+    obj1.stub!(:eql?).and_return(true)
     obj2.stub!(:eql?).and_return(true)
 
-    [obj1].send(@method, [obj2]).should == [obj1]
-    [obj1, obj1, obj2, obj2].send(@method, [obj2]).should == [obj1]
+    # we cannot expect some particular object in the result array
+    # because it's an implementation details which array to iterate and both obj1 and obj2 is a correct result
+    [obj1].send(@method, [obj2]).size.should == 1
+    [obj1, obj1, obj2, obj2].send(@method, [obj2]).size.should == 1
 
     obj1 = mock('3')
     obj2 = mock('4')
     obj1.stub!(:hash).and_return(0)
     obj2.stub!(:hash).and_return(0)
-    obj1.should_receive(:eql?).at_least(1).and_return(false)
+    obj1.stub!(:eql?).and_return(false)
+    obj2.stub!(:eql?).and_return(false)
 
     [obj1].send(@method, [obj2]).should == []
     [obj1, obj1, obj2, obj2].send(@method, [obj2]).should == [obj2]
diff --git a/src/main/ruby/truffleruby/core/array.rb b/src/main/ruby/truffleruby/core/array.rb
index 2c07ca0ca375..37261bfd20d4 100644
--- a/src/main/ruby/truffleruby/core/array.rb
+++ b/src/main/ruby/truffleruby/core/array.rb
@@ -59,10 +59,14 @@ def self.try_convert(obj)
 
   def &(other)
     other = Truffle::Type.coerce_to other, Array, :to_ary
+    return [] if size == 0 || other.size == 0
 
-    h = {}
-    other.each { |e| h[e] = true }
-    select { |x| h.delete x }
+    shorter, longer = size > other.size ? [other, self] : [self, other]
+
+    shorter_set = {}
+    shorter.each { |e| shorter_set[e] = true }
+
+    longer.select { |e| shorter_set.delete e }
   end
 
   def |(other)
@@ -615,6 +619,7 @@ def inspect
   alias_method :to_s, :inspect
 
   def intersect?(other)
+    other = Truffle::Type.coerce_to other, Array, :to_ary
     return false if size == 0 || other.size == 0
 
     shorter, longer = size > other.size ? [other, self] : [self, other]