[GSoC] Use a compact hash table for RubyHash instead of the buckets strategy

CHANGELOG.md

@@ -21,6 +21,7 @@ Compatibility:
 
 Performance:
 
+* Change the `Hash` representation from traditional buckets to a "compact hash table" for improved locality, performance and memory footprint (#3172, @moste00).
 * Optimize calls with `ruby2_keywords` forwarding by deciding it per call site instead of per callee thanks to [my fix in CRuby 3.2](https://bugs.ruby-lang.org/issues/18625) (@eregon).
 * Optimize feature loading when require is called with an absolute path to a .rb file (@rwstauner).
 

bench/micro/hash/buckets-lookup.rb

@@ -0,0 +1,23 @@
+# truffleruby_primitives: true
+
+# Copyright (c) 2023 Oracle and/or its affiliates. All rights reserved. This
+# code is released under a tri EPL/GPL/LGPL license. You can use it,
+# redistribute it and/or modify it under the terms of the:
+#
+# Eclipse Public License version 2.0, or
+# GNU General Public License version 2, or
+# GNU Lesser General Public License version 2.1.
+
+# Benchmarks looking up keys
+
+max = 400_000 # > 0.75*(524288 + 21) (cf. BucketsHashStore)
+hash = { a: 1, b: 2, c: 3, d: 4 } # big enough to start as a bucket hash
+max.times { |i|
+  hash[i] = i
+}
+
+benchmark 'core-hash-buckets-lookup' do
+  1000.times do |i|
+    Primitive.blackhole(hash[i])
+  end
+end

bench/micro/hash/each-buckets.rb

@@ -13,6 +13,6 @@
 if RUBY_ENGINE == 'truffleruby'
   hash = { a: 1, b: 2, c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10 }
   benchmark 'core-hash-each-buckets' do
-    hash.each { |k, v| Primitive.blackhole(v) }
+    hash.each { |k, v| Primitive.blackhole(k); Primitive.blackhole(v) }
   end
 end

spec/ruby/core/hash/delete_spec.rb

@@ -24,21 +24,35 @@
   it "allows removing a key while iterating" do
     h = { a: 1, b: 2 }
     visited = []
-    h.each_pair { |k,v|
+    h.each_pair { |k, v|
       visited << k
       h.delete(k)
     }
     visited.should == [:a, :b]
     h.should == {}
   end
 
+  it "allows removing a key while iterating for big hashes" do
+    h = { a: 1, b: 2, c: 3, d: 4, e: 5, f: 6, g: 7, h: 8, i: 9, j: 10,
+          k: 11, l: 12, m: 13, n: 14, o: 15, p: 16, q: 17, r: 18, s: 19, t: 20,
+          u: 21, v: 22, w: 23, x: 24, y: 25, z: 26 }
+    visited = []
+    h.each_pair { |k, v|
+      visited << k
+      h.delete(k)
+    }
+    visited.should == [:a, :b, :c, :d, :e, :f, :g, :h, :i, :j, :k, :l, :m,
+                       :n, :o, :p, :q, :r, :s, :t, :u, :v, :w, :x, :y, :z]
+    h.should == {}
+  end
+
   it "accepts keys with private #hash method" do
     key = HashSpecs::KeyWithPrivateHash.new
     { key => 5 }.delete(key).should == 5
   end
 
   it "raises a FrozenError if called on a frozen instance" do
-    -> { HashSpecs.frozen_hash.delete("foo")  }.should raise_error(FrozenError)
+    -> { HashSpecs.frozen_hash.delete("foo") }.should raise_error(FrozenError)
     -> { HashSpecs.empty_frozen_hash.delete("foo") }.should raise_error(FrozenError)
   end
 end

spec/ruby/core/hash/rehash_spec.rb

@@ -77,6 +77,36 @@ def k1.hash; 1; end
     h.keys.should_not.include? [1]
   end
 
+  it "iterates keys in insertion order" do
+    key = Class.new do
+      attr_reader :name
+
+      def initialize(name)
+        @name = name
+      end
+
+      def hash
+        123
+      end
+    end
+
+    a, b, c, d = key.new('a'), key.new('b'), key.new('c'), key.new('d')
+    h = { a => 1, b => 2, c => 3, d => 4 }
+    h.size.should == 4
+
+    key.class_exec do
+      def eql?(other)
+        true
+      end
+    end
+
+    h.rehash
+    h.size.should == 1
+    k, v = h.first
+    k.name.should == 'a'
+    v.should == 4
+  end
+
   it "raises a FrozenError if called on a frozen instance" do
     -> { HashSpecs.frozen_hash.rehash  }.should raise_error(FrozenError)
     -> { HashSpecs.empty_frozen_hash.rehash }.should raise_error(FrozenError)

src/main/java/org/truffleruby/core/array/ArrayNodes.java

@@ -909,46 +909,46 @@ Object equalNotArray(RubyArray a, Object b) {
     @ImportStatic(ArrayGuards.class)
     public abstract static class EqlNode extends PrimitiveArrayArgumentsNode {
 
-        @Child private SameOrEqlNode eqlNode = SameOrEqlNode.create();
-
         @Specialization(
                 guards = { "stores.accepts(bStore)", "stores.isPrimitive(aStore)" },
                 limit = "storageStrategyLimit()")
-        boolean eqlSamePrimitiveType(RubyArray a, RubyArray b,
+        static boolean eqlSamePrimitiveType(RubyArray a, RubyArray b,
                 @Bind("a.getStore()") Object aStore,
                 @Bind("b.getStore()") Object bStore,
                 @CachedLibrary("aStore") ArrayStoreLibrary stores,
-                @Cached ConditionProfile sameProfile,
-                @Cached IntValueProfile arraySizeProfile,
-                @Cached ConditionProfile sameSizeProfile,
-                @Cached BranchProfile trueProfile,
-                @Cached BranchProfile falseProfile,
-                @Cached LoopConditionProfile loopProfile) {
+                @Cached SameOrEqlNode eqlNode,
+                @Cached InlinedConditionProfile sameProfile,
+                @Cached InlinedIntValueProfile arraySizeProfile,
+                @Cached InlinedConditionProfile sameSizeProfile,
+                @Cached InlinedBranchProfile trueProfile,
+                @Cached InlinedBranchProfile falseProfile,
+                @Cached InlinedLoopConditionProfile loopProfile,
+                @Bind("$node") Node node) {
 
-            if (sameProfile.profile(a == b)) {
+            if (sameProfile.profile(node, a == b)) {
                 return true;
             }
 
-            final int size = arraySizeProfile.profile(a.size);
+            final int size = arraySizeProfile.profile(node, a.size);
 
-            if (!sameSizeProfile.profile(size == b.size)) {
+            if (!sameSizeProfile.profile(node, size == b.size)) {
                 return false;
             }
 
             int i = 0;
             try {
-                for (; loopProfile.inject(i < size); i++) {
-                    if (!eqlNode.execute(stores.read(aStore, i), stores.read(bStore, i))) {
-                        falseProfile.enter();
+                for (; loopProfile.inject(node, i < size); i++) {
+                    if (!eqlNode.execute(node, stores.read(aStore, i), stores.read(bStore, i))) {
+                        falseProfile.enter(node);
                         return false;
                     }
-                    TruffleSafepoint.poll(this);
+                    TruffleSafepoint.poll(node);
                 }
             } finally {
-                profileAndReportLoopCount(loopProfile, i);
+                profileAndReportLoopCount(node, loopProfile, i);
             }
 
-            trueProfile.enter();
+            trueProfile.enter(node);
             return true;
         }
 

src/main/java/org/truffleruby/core/hash/CompareHashKeysNode.java

@@ -9,22 +9,23 @@
  */
 package org.truffleruby.core.hash;
 
+import com.oracle.truffle.api.dsl.GenerateCached;
+import com.oracle.truffle.api.dsl.GenerateInline;
+import org.truffleruby.core.basicobject.ReferenceEqualNode;
+import org.truffleruby.core.kernel.KernelNodes.SameOrEqlNode;
+import org.truffleruby.language.RubyBaseNode;
+
 import com.oracle.truffle.api.dsl.Cached;
 import com.oracle.truffle.api.dsl.GenerateUncached;
 import com.oracle.truffle.api.dsl.Specialization;
 import com.oracle.truffle.api.nodes.Node;
-import org.truffleruby.core.basicobject.ReferenceEqualNode;
-import org.truffleruby.core.kernel.KernelNodes.SameOrEqlNode;
-import org.truffleruby.language.RubyBaseNode;
 
+@GenerateInline
+@GenerateCached(false)
 @GenerateUncached
 public abstract class CompareHashKeysNode extends RubyBaseNode {
 
-    public static CompareHashKeysNode getUncached() {
-        return CompareHashKeysNodeGen.getUncached();
-    }
-
-    public abstract boolean execute(boolean compareByIdentity, Object key, int hashed,
+    public abstract boolean execute(Node node, boolean compareByIdentity, Object key, int hashed,
             Object otherKey, int otherHashed);
 
     /** Checks if the two keys are the same object, which is used by both modes (by identity or not) of lookup. Enables
@@ -37,14 +38,35 @@ public static boolean referenceEqualKeys(Node node, ReferenceEqualNode refEqual,
     }
 
     @Specialization(guards = "compareByIdentity")
-    boolean refEquals(boolean compareByIdentity, Object key, int hashed, Object otherKey, int otherHashed,
+    static boolean refEquals(
+            Node node, boolean compareByIdentity, Object key, int hashed, Object otherKey, int otherHashed,
             @Cached ReferenceEqualNode refEqual) {
-        return refEqual.execute(this, key, otherKey);
+        return refEqual.execute(node, key, otherKey);
     }
 
     @Specialization(guards = "!compareByIdentity")
-    boolean same(boolean compareByIdentity, Object key, int hashed, Object otherKey, int otherHashed,
+    static boolean same(Node node, boolean compareByIdentity, Object key, int hashed, Object otherKey, int otherHashed,
             @Cached SameOrEqlNode same) {
-        return hashed == otherHashed && same.execute(key, otherKey);
+        return hashed == otherHashed && same.execute(node, key, otherKey);
+    }
+
+    @GenerateInline
+    @GenerateCached(false)
+    @GenerateUncached
+    public abstract static class AssumingEqualHashes extends RubyBaseNode {
+
+        public abstract boolean execute(Node node, boolean compareByIdentity, Object key, Object otherKey);
+
+        @Specialization(guards = "compareByIdentity")
+        static boolean refEquals(Node node, boolean compareByIdentity, Object key, Object otherKey,
+                @Cached ReferenceEqualNode refEqual) {
+            return refEqual.execute(node, key, otherKey);
+        }
+
+        @Specialization(guards = "!compareByIdentity")
+        static boolean same(Node node, boolean compareByIdentity, Object key, Object otherKey,
+                @Cached SameOrEqlNode same) {
+            return same.execute(node, key, otherKey);
+        }
     }
 }

src/main/java/org/truffleruby/core/hash/HashLiteralNode.java

@@ -9,7 +9,9 @@
  */
 package org.truffleruby.core.hash;
 
+import org.truffleruby.RubyLanguage;
 import org.truffleruby.core.hash.library.BucketsHashStore;
+import org.truffleruby.core.hash.library.CompactHashStore;
 import org.truffleruby.core.hash.library.EmptyHashStore;
 import org.truffleruby.core.hash.library.PackedHashStoreLibrary;
 import org.truffleruby.core.hash.library.PackedHashStoreLibraryFactory;
@@ -28,13 +30,19 @@ protected HashLiteralNode(RubyNode[] keyValues) {
         this.keyValues = keyValues;
     }
 
-    public static HashLiteralNode create(RubyNode[] keyValues) {
+    protected int getNumberOfEntries() {
+        return keyValues.length >> 1;
+    }
+
+    public static HashLiteralNode create(RubyNode[] keyValues, RubyLanguage language) {
         if (keyValues.length == 0) {
             return new EmptyHashStore.EmptyHashLiteralNode();
         } else if (keyValues.length <= PackedHashStoreLibrary.MAX_ENTRIES * 2) {
             return PackedHashStoreLibraryFactory.SmallHashLiteralNodeGen.create(keyValues);
         } else {
-            return new BucketsHashStore.GenericHashLiteralNode(keyValues);
+            return language.options.BIG_HASH_STRATEGY_IS_BUCKETS
+                    ? new BucketsHashStore.BucketHashLiteralNode(keyValues)
+                    : new CompactHashStore.CompactHashLiteralNode(keyValues);
         }
     }
 

src/main/java/org/truffleruby/core/hash/RubyHash.java

@@ -11,6 +11,20 @@
 
 import java.util.Set;
 
+import org.truffleruby.RubyContext;
+import org.truffleruby.collections.PEBiFunction;
+import org.truffleruby.core.hash.library.BucketsHashStore;
+import org.truffleruby.core.hash.library.CompactHashStore;
+import org.truffleruby.core.hash.library.HashStoreLibrary;
+import org.truffleruby.core.klass.RubyClass;
+import org.truffleruby.interop.ForeignToRubyNode;
+import org.truffleruby.language.Nil;
+import org.truffleruby.language.RubyDynamicObject;
+import org.truffleruby.language.dispatch.DispatchNode;
+import org.truffleruby.language.objects.IsFrozenNode;
+import org.truffleruby.language.objects.ObjectGraph;
+import org.truffleruby.language.objects.ObjectGraphNode;
+
 import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
 import com.oracle.truffle.api.dsl.Bind;
 import com.oracle.truffle.api.dsl.Cached;
@@ -26,20 +40,7 @@
 import com.oracle.truffle.api.library.ExportMessage;
 import com.oracle.truffle.api.nodes.Node;
 import com.oracle.truffle.api.object.Shape;
-
 import com.oracle.truffle.api.profiles.InlinedConditionProfile;
-import org.truffleruby.RubyContext;
-import org.truffleruby.collections.PEBiFunction;
-import org.truffleruby.core.hash.library.BucketsHashStore;
-import org.truffleruby.core.hash.library.HashStoreLibrary;
-import org.truffleruby.core.klass.RubyClass;
-import org.truffleruby.interop.ForeignToRubyNode;
-import org.truffleruby.language.Nil;
-import org.truffleruby.language.RubyDynamicObject;
-import org.truffleruby.language.dispatch.DispatchNode;
-import org.truffleruby.language.objects.IsFrozenNode;
-import org.truffleruby.language.objects.ObjectGraph;
-import org.truffleruby.language.objects.ObjectGraphNode;
 
 @ExportLibrary(InteropLibrary.class)
 @ImportStatic(HashGuards.class)
@@ -86,6 +87,8 @@ public String toString() {
     public void getAdjacentObjects(Set<Object> reachable) {
         if (store instanceof BucketsHashStore) {
             ((BucketsHashStore) store).getAdjacentObjects(reachable);
+        } else if (store instanceof CompactHashStore) {
+            ((CompactHashStore) store).getAdjacentObjects(reachable);
         } else {
             ObjectGraph.addProperty(reachable, store);
         }