PaperMC/patches/server-remapped/0462-Optimize-Voxel-Shape-Merging.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Sun, 3 May 2020 22:35:09 -0400
Subject: [PATCH] Optimize Voxel Shape Merging

This method shows up as super hot in profiler, and also a high "self" time.

Upon analyzing, it appears most usages of this method fall down to the final
else statement of the nasty ternary.

Upon even further analyzation, it appears then the majority of those have a
consistent list 1.... One with Infinity head and Tails.

First optimization is to detect these infinite states and immediately return that
VoxelShapeMergerList so we can avoid testing the rest for most cases.

Break the method into 2 to help the JVM promote inlining of this fast path.

Then it was also noticed that VoxelShapeMergerList constructor is also a hotspot
with a high self time...

Well, knowing that in most cases our list 1 is actualy the same value, it allows
us to know that with an infinite list1, the result on the merger is essentially
list2 as the final values.

This let us analyze the 2 potential states (Infinite with 2 sources or 4 sources)
and compute a deterministic result for the MergerList values.

Additionally, this lets us avoid even allocating new objects for this too, further
reducing memory usage.

diff --git a/src/main/java/net/minecraft/world/phys/shapes/IndirectMerger.java b/src/main/java/net/minecraft/world/phys/shapes/IndirectMerger.java
index f0e74daa5bb9e88c028225e7c71deb04c481a7ac..abbe05b07831423eccf8779e854251dec5fbc2ae 100644
--- a/src/main/java/net/minecraft/world/phys/shapes/IndirectMerger.java
+++ b/src/main/java/net/minecraft/world/phys/shapes/IndirectMerger.java
@@ -6,10 +6,16 @@ import it.unimi.dsi.fastutil.ints.IntArrayList;
 
 public final class IndirectMerger implements IndexMerger {
 
-    private final DoubleArrayList result;
+    private final DoubleList a; // Paper
     private final IntArrayList firstIndices;
     private final IntArrayList secondIndices;
 
+    // Paper start
+    private static final IntArrayList INFINITE_B_1 = new IntArrayList(new int[]{1, 1});
+    private static final IntArrayList INFINITE_B_0 = new IntArrayList(new int[]{0, 0});
+    private static final IntArrayList INFINITE_C = new IntArrayList(new int[]{0, 1});
+    // Paper end
+
     protected IndirectMerger(DoubleList first, DoubleList second, boolean includeFirstOnly, boolean includeSecondOnly) {
         int i = 0;
         int j = 0;
@@ -18,7 +24,23 @@ public final class IndirectMerger implements IndexMerger {
         int l = second.size();
         int i1 = k + l;
 
-        this.result = new DoubleArrayList(i1);
+        // Paper start - optimize common path of infinity doublelist
+        int size = first.size();
+        double tail = first.getDouble(size - 1);
+        double head = first.getDouble(0);
+        if (head == Double.NEGATIVE_INFINITY && tail == Double.POSITIVE_INFINITY && !includeFirstOnly && !includeSecondOnly && (size == 2 || size == 4)) {
+            this.a = second;
+            if (size == 2) {
+                this.firstIndices = INFINITE_B_0;
+            } else {
+                this.firstIndices = INFINITE_B_1;
+            }
+            this.secondIndices = INFINITE_C;
+            return;
+        }
+        // Paper end
+
+        this.a = new DoubleArrayList(i1);
         this.firstIndices = new IntArrayList(i1);
         this.secondIndices = new IntArrayList(i1);
 
@@ -27,8 +49,8 @@ public final class IndirectMerger implements IndexMerger {
             boolean flag3 = j < l;
 
             if (!flag2 && !flag3) {
-                if (this.result.isEmpty()) {
-                    this.result.add(Math.min(first.getDouble(k - 1), second.getDouble(l - 1)));
+                if (this.a.isEmpty()) {
+                    this.a.add(Math.min(first.getDouble(k - 1), second.getDouble(l - 1)));
                 }
 
                 return;
@@ -41,9 +63,9 @@ public final class IndirectMerger implements IndexMerger {
                 if (!(d0 >= d1 - 1.0E-7D)) { // Paper - decompile error - welcome to hell
                     this.firstIndices.add(i - 1);
                     this.secondIndices.add(j - 1);
-                    this.result.add(d1);
+                    this.a.add(d1);
                     d0 = d1;
-                } else if (!this.result.isEmpty()) {
+                } else if (!this.a.isEmpty()) {
                     this.firstIndices.set(this.firstIndices.size() - 1, i - 1);
                     this.secondIndices.set(this.secondIndices.size() - 1, j - 1);
                 }
@@ -53,7 +75,7 @@ public final class IndirectMerger implements IndexMerger {
 
     @Override
     public boolean forMergedIndexes(IndexMerger.IndexConsumer predicate) {
-        for (int i = 0; i < this.result.size() - 1; ++i) {
+        for (int i = 0; i < this.a.size() - 1; ++i) {
             if (!predicate.merge(this.firstIndices.getInt(i), this.secondIndices.getInt(i), i)) {
                 return false;
             }
@@ -64,6 +86,6 @@ public final class IndirectMerger implements IndexMerger {
 
     @Override
     public DoubleList getList() {
-        return this.result;
+        return this.a;
     }
 }
diff --git a/src/main/java/net/minecraft/world/phys/shapes/Shapes.java b/src/main/java/net/minecraft/world/phys/shapes/Shapes.java
index c14d5ebe16a693834ed218af8f737714065b2e17..1603eb3f7d90a4b3a028b20776566db77d09c123 100644
--- a/src/main/java/net/minecraft/world/phys/shapes/Shapes.java
+++ b/src/main/java/net/minecraft/world/phys/shapes/Shapes.java
@@ -329,19 +329,46 @@ public final class Shapes {
     }
 
     @VisibleForTesting
-    protected static IndexMerger createIndexMerger(int size, DoubleList first, DoubleList second, boolean includeFirst, boolean includeSecond) {
-        int j = first.size() - 1;
-        int k = second.size() - 1;
+    private static IndexMerger createIndexMerger(int size, DoubleList first, DoubleList second, boolean includeFirst, boolean includeSecond) { // Paper - private
+        // Paper start - fast track the most common scenario
+        // doublelist is usually a DoubleArrayList with Infinite head/tails that falls to the final else clause
+        // This is actually the most common path, so jump to it straight away
+        if (first.getDouble(0) == Double.NEGATIVE_INFINITY && first.getDouble(first.size() - 1) == Double.POSITIVE_INFINITY) {
+            return new IndirectMerger(first, second, includeFirst, includeSecond);
+        }
+        // Split out rest to hopefully inline the above
+        return lessCommonMerge(size, first, second, includeFirst, includeSecond);
+    }
+
+    private static IndexMerger lessCommonMerge(int i, DoubleList doublelist, DoubleList doublelist1, boolean flag, boolean flag1) {
+        int j = doublelist.size() - 1;
+        int k = doublelist1.size() - 1;
+        // Paper note - Rewrite below as optimized order if instead of nasty ternary
 
-        if (first instanceof CubePointRange && second instanceof CubePointRange) {
+        if (doublelist instanceof CubePointRange && doublelist1 instanceof CubePointRange) {
             long l = lcm(j, k);
 
-            if ((long) size * l <= 256L) {
+            if ((long) i * l <= 256L) {
                 return new DiscreteCubeMerger(j, k);
             }
         }
 
-        return (IndexMerger) (first.getDouble(j) < second.getDouble(0) - 1.0E-7D ? new NonOverlappingMerger(first, second, false) : (second.getDouble(k) < first.getDouble(0) - 1.0E-7D ? new NonOverlappingMerger(second, first, true) : (j == k && Objects.equals(first, second) ? (first instanceof IdenticalMerger ? (IndexMerger) first : (second instanceof IdenticalMerger ? (IndexMerger) second : new IdenticalMerger(first))) : new IndirectMerger(first, second, includeFirst, includeSecond))));
+        // Identical happens more often than Disjoint
+        if (j == k && Objects.equals(doublelist, doublelist1)) {
+            if (doublelist instanceof IdenticalMerger) {
+                return (IndexMerger) doublelist;
+            } else if (doublelist1 instanceof IdenticalMerger) {
+                return (IndexMerger) doublelist1;
+            }
+            return new IdenticalMerger(doublelist);
+        } else if (doublelist.getDouble(j) < doublelist1.getDouble(0) - 1.0E-07) {
+            return new NonOverlappingMerger(doublelist, doublelist1, false);
+        } else if (doublelist1.getDouble(k) < doublelist.getDouble(0) - 1.0E-07) {
+            return new NonOverlappingMerger(doublelist1, doublelist, true);
+        } else {
+            return new IndirectMerger(doublelist, doublelist1, flag, flag1);
+        }
+        // Paper end
     }
 
     public interface DoubleLineConsumer {