From 729fcdb616344ee265cc6ebb104db68ce4a48d9a Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Fri, 14 Jun 2024 16:00:08 -0700
Subject: [PATCH] Avoid some insertions in point clears

---
 VersionedMap.cpp | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

diff --git a/VersionedMap.cpp b/VersionedMap.cpp
index 933da46..8cfc416 100644
--- a/VersionedMap.cpp
+++ b/VersionedMap.cpp
@@ -902,19 +902,34 @@ struct __attribute__((__visibility__("hidden"))) VersionedMap::Impl {
         if (m.param2Len == 0) {
           search<std::memory_order_relaxed>({m.param1, m.param1Len}, latestRoot,
                                             latestVersion, iter);
-          insert({m.param1, m.param1Len}, {{nullptr, -1}}, iter);
+          const bool found = iter.searchPathSize() > 0 && iter.backNode() != 0;
 
-          const bool engulfLeft = mm.base[iter.backNode()].entry->clearTo();
-          move<std::memory_order_relaxed, true>(iter, latestVersion);
-          const auto *next = iter.searchPathSize() > 0
-                                 ? mm.base[iter.backNode()].entry
-                                 : nullptr;
-          if (engulfLeft && next && next->clearTo()) {
-            insert({next->getKey(), next->keyLen}, {}, iter);
-            move<std::memory_order_relaxed, false>(iter, latestVersion);
-            remove(iter);
+          bool engulfLeft = found && mm.base[iter.backNode()].entry->clearTo();
+          bool engulfRight = false;
+          const Entry *next;
+          Finger copy;
+
+          if (iter.searchPathSize() > 0) {
+            iter.copyTo(copy);
+            move<std::memory_order_relaxed, true>(copy, latestVersion);
+            next = copy.searchPathSize() > 0 ? mm.base[copy.backNode()].entry
+                                             : nullptr;
+            if (next && next->clearTo()) {
+              engulfRight = true;
+              if (!found) {
+                engulfLeft = true;
+              }
+            }
           }
 
+          if (engulfLeft && engulfRight) {
+            insert({next->getKey(), next->keyLen}, {}, copy);
+            if (found) {
+              remove(iter);
+            }
+          } else {
+            insert({m.param1, m.param1Len}, {{nullptr, -1}}, iter);
+          }
         } else {
           search<std::memory_order_relaxed>({m.param1, m.param1Len}, latestRoot,
                                             latestVersion, iter);