From 305c2188884e26ad0b4f2b3cd3debeb96c149d2f Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Fri, 23 Feb 2024 14:27:20 -0800
Subject: [PATCH] Skip checking for partial key match if partial key len == 0

This saves instructions according to cachegrind
---
 ConflictSet.cpp | 63 ++++++++++++++++++++++++++-----------------------
 1 file changed, 34 insertions(+), 29 deletions(-)

diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index 86b5b26..cca8b50 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -1411,39 +1411,44 @@ bool checkRangeRead(Node *n, std::span<const uint8_t> begin,
 template <bool kBegin>
 [[nodiscard]] Node *insert(Node **self, std::span<const uint8_t> key,
                            int64_t writeVersion, NodeAllocators *allocators) {
+
   for (;;) {
-    // Handle an existing partial key
-    int commonLen = std::min<int>((*self)->partialKeyLen, key.size());
-    int partialKeyIndex = longestCommonPrefixPartialKey((*self)->partialKey,
-                                                        key.data(), commonLen);
-    if (partialKeyIndex < (*self)->partialKeyLen) {
-      auto *old = *self;
 
-      *self = allocators->node4.allocate();
+    if ((*self)->partialKeyLen > 0) {
+      // Handle an existing partial key
+      int commonLen = std::min<int>((*self)->partialKeyLen, key.size());
+      int partialKeyIndex = longestCommonPrefixPartialKey(
+          (*self)->partialKey, key.data(), commonLen);
+      if (partialKeyIndex < (*self)->partialKeyLen) {
+        auto *old = *self;
 
-      memcpy((void *)*self, old, offsetof(Node, type));
-      (*self)->partialKeyLen = partialKeyIndex;
-      (*self)->entryPresent = false;
-      (*self)->numChildren = 0;
+        *self = allocators->node4.allocate();
 
-      getOrCreateChild(*self, old->partialKey[partialKeyIndex], allocators) =
-          old;
-      old->parent = *self;
-      old->parentsIndex = old->partialKey[partialKeyIndex];
+        memcpy((void *)*self, old, offsetof(Node, type));
+        (*self)->partialKeyLen = partialKeyIndex;
+        (*self)->entryPresent = false;
+        (*self)->numChildren = 0;
 
-      memmove(old->partialKey, old->partialKey + partialKeyIndex + 1,
-              old->partialKeyLen - (partialKeyIndex + 1));
-      old->partialKeyLen -= partialKeyIndex + 1;
-    }
-    key = key.subspan(partialKeyIndex, key.size() - partialKeyIndex);
+        getOrCreateChild(*self, old->partialKey[partialKeyIndex], allocators) =
+            old;
+        old->parent = *self;
+        old->parentsIndex = old->partialKey[partialKeyIndex];
 
-    // Consider adding a partial key
-    if ((*self)->numChildren == 0 && !(*self)->entryPresent) {
-      (*self)->partialKeyLen =
-          std::min<int>(key.size(), (*self)->kPartialKeyMaxLen);
-      memcpy((*self)->partialKey, key.data(), (*self)->partialKeyLen);
-      key = key.subspan((*self)->partialKeyLen,
-                        key.size() - (*self)->partialKeyLen);
+        memmove(old->partialKey, old->partialKey + partialKeyIndex + 1,
+                old->partialKeyLen - (partialKeyIndex + 1));
+        old->partialKeyLen -= partialKeyIndex + 1;
+      }
+      key = key.subspan(partialKeyIndex, key.size() - partialKeyIndex);
+
+    } else {
+      // Consider adding a partial key
+      if ((*self)->numChildren == 0 && !(*self)->entryPresent) {
+        (*self)->partialKeyLen =
+            std::min<int>(key.size(), (*self)->kPartialKeyMaxLen);
+        memcpy((*self)->partialKey, key.data(), (*self)->partialKeyLen);
+        key = key.subspan((*self)->partialKeyLen,
+                          key.size() - (*self)->partialKeyLen);
+      }
     }
 
     if constexpr (kBegin) {
@@ -1458,10 +1463,10 @@ template <bool kBegin>
       (*self)->maxVersion = std::max((*self)->maxVersion, writeVersion);
     }
 
-    auto &child = getOrCreateChild((*self), key.front(), allocators);
+    auto &child = getOrCreateChild(*self, key.front(), allocators);
     if (!child) {
       child = allocators->node4.allocate();
-      child->parent = (*self);
+      child->parent = *self;
       child->parentsIndex = key.front();
       child->maxVersion =
           kBegin ? writeVersion : std::numeric_limits<int64_t>::lowest();