Optimize SortedArraySet.removeIf

src/main/java/org/embeddedt/modernfix/mixin/bugfix/paper_chunk_patches/SortedArraySetMixin.java

@@ -0,0 +1,51 @@
+package org.embeddedt.modernfix.mixin.bugfix.paper_chunk_patches;
+
+import net.minecraft.util.SortedArraySet;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+
+import java.util.AbstractSet;
+import java.util.Arrays;
+import java.util.function.Predicate;
+
+@Mixin(SortedArraySet.class)
+public abstract class SortedArraySetMixin<T> extends AbstractSet<T> {
+    @Shadow private int size;
+
+    @Shadow private T[] contents;
+
+    // Paper start - optimise removeIf
+    @Override
+    public boolean removeIf(Predicate<? super T> filter) {
+        // prev. impl used an iterator, which could be n^2 and creates garbage
+        int i = 0, len = this.size;
+        T[] backingArray = this.contents;
+
+        for (;;) {
+            if (i >= len) {
+                return false;
+            }
+            if (!filter.test(backingArray[i])) {
+                ++i;
+                continue;
+            }
+            break;
+        }
+
+        // we only want to write back to backingArray if we really need to
+
+        int lastIndex = i; // this is where new elements are shifted to
+
+        for (; i < len; ++i) {
+            T curr = backingArray[i];
+            if (!filter.test(curr)) { // if test throws we're screwed
+                backingArray[lastIndex++] = curr;
+            }
+        }
+
+        // cleanup end
+        Arrays.fill(backingArray, lastIndex, len, null);
+        this.size = lastIndex;
+        return true;
+    }
+}

src/main/resources/modernfix.mixins.json

@@ -11,6 +11,7 @@
     "bugfix.starlight_emptiness.StarLightEngineMixin",
     "bugfix.paper_chunk_patches.ChunkMapMixin",
     "bugfix.paper_chunk_patches.ChunkHolderMixin",
+    "bugfix.paper_chunk_patches.SortedArraySetMixin",
     "perf.dynamic_structure_manager.StructureManagerMixin",
     "bugfix.tf_cme_on_load.TwilightForestModMixin",
     "bugfix.refinedstorage.te_bug.ItemExternalStorageProviderMixin",