From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Mon, 15 May 2023 20:25:26 -0700
Subject: [PATCH] Optimise recalcBlockCounts() for empty sections

In 1.18, every chunk section is initialised to a non-null value
and recalcBlockCounts() is invoked for each section.
However, in a standard world, most sections are empty. In such cases,
recalcBlockCounts() would iterate over ever position - even though
the block data would all be air. To avoid this, we skip
searching the section unless the palette indicates there _could_ be
a non-air block state or non-empty fluid state.

Chunk loading initially showed that recalcBlockCounts() over
sections with a ZeroBitStorage data to to take ~20% of the process,
now it takes <1%.

diff --git a/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java b/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
index f150a16fbf888455301d8b9043f0b45fb1fa1d84..fd4c4122e3811c8f5d8c02f8faaf3579bcb8ad79 100644
--- a/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
+++ b/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
@@ -229,6 +229,7 @@ public class LevelChunkSection {
         this.nonEmptyBlockCount = 0;
         this.tickingBlockCount = 0;
         this.tickingFluidCount = 0;
+        if (this.maybeHas((BlockState state) -> !state.isAir() || !state.getFluidState().isEmpty())) { // Paper - do not run forEachLocation on clearly empty sections
         this.states.forEachLocation((BlockState iblockdata, int i) -> {
             FluidState fluid = iblockdata.getFluidState();
 
@@ -248,6 +249,7 @@ public class LevelChunkSection {
             }
 
         });
+        } // Paper - do not run forEachLocation on clearly empty sections
         // Paper end
         this.initBlockCollisionData(); // Paper
     }