additional optimizations

src/lib/class-group-utils.ts

@@ -57,26 +57,32 @@ export const createClassGroupUtils = (config: AnyConfig) => {
         }
 
         const classParts = className.split(CLASS_PART_SEPARATOR)
-        // Classes like `-inset-1` produce an empty string as first classPart. We assume that classes for negative values are used correctly and remove it from classParts.
-        if (classParts[0] === '' && classParts.length > 1) {
-            classParts.shift()
-        }
-        return getGroupRecursive(classParts, classMap)
+        // Classes like `-inset-1` produce an empty string as first classPart. We assume that classes for negative values are used correctly and skip it.
+        const startIndex = classParts[0] === '' && classParts.length > 1 ? 1 : 0
+        return getGroupRecursive(classParts, startIndex, classMap)
     }
 
     const getConflictingClassGroupIds = (
         classGroupId: AnyClassGroupIds,
         hasPostfixModifier: boolean,
     ): readonly AnyClassGroupIds[] => {
-        const conflicts = conflictingClassGroups[classGroupId]
-        if (!hasPostfixModifier || !conflictingClassGroupModifiers[classGroupId]) {
-            return conflicts || EMPTY_CONFLICTS
+        if (hasPostfixModifier) {
+            const modifierConflicts = conflictingClassGroupModifiers[classGroupId]
+            const baseConflicts = conflictingClassGroups[classGroupId]
+
+            if (modifierConflicts) {
+                if (baseConflicts) {
+                    // Merge base conflicts with modifier conflicts
+                    return concatArrays(baseConflicts, modifierConflicts)
+                }
+                // Only modifier conflicts
+                return modifierConflicts
+            }
+            // Fall back to without postfix if no modifier conflicts
+            return baseConflicts || EMPTY_CONFLICTS
         }
 
-        const modifierConflicts = conflictingClassGroupModifiers[classGroupId]!
-        if (!conflicts) return modifierConflicts
-
-        return concatArrays(conflicts, modifierConflicts)
+        return conflictingClassGroups[classGroupId] || EMPTY_CONFLICTS
     }
 
     return {
@@ -87,18 +93,19 @@ export const createClassGroupUtils = (config: AnyConfig) => {
 
 const getGroupRecursive = (
     classParts: string[],
+    startIndex: number,
     classPartObject: ClassPartObject,
 ): AnyClassGroupIds | undefined => {
-    const classPathsLength = classParts.length
+    const classPathsLength = classParts.length - startIndex
     if (classPathsLength === 0) {
         return classPartObject.classGroupId
     }
 
-    const currentClassPart = classParts[0]!
+    const currentClassPart = classParts[startIndex]!
     const nextClassPartObject = classPartObject.nextPart.get(currentClassPart)
 
     if (nextClassPartObject) {
-        const result = getGroupRecursive(classParts.slice(1), nextClassPartObject)
+        const result = getGroupRecursive(classParts, startIndex + 1, nextClassPartObject)
         if (result) return result
     }
 
@@ -107,7 +114,11 @@ const getGroupRecursive = (
         return undefined
     }
 
-    const classRest = classParts.join(CLASS_PART_SEPARATOR)
+    // Build classRest string efficiently by joining from startIndex onwards
+    const classRest =
+        startIndex === 0
+            ? classParts.join(CLASS_PART_SEPARATOR)
+            : classParts.slice(startIndex).join(CLASS_PART_SEPARATOR)
     const validatorsLength = validators.length
 
     for (let i = 0; i < validatorsLength; i++) {

src/lib/merge-classlist.ts

@@ -60,7 +60,13 @@ export const mergeClassList = (classList: string, configUtils: ConfigUtils) => {
             hasPostfixModifier = false
         }
 
-        const variantModifier = sortModifiers(modifiers).join(':')
+        // Fast path: skip sorting for empty or single modifier
+        const variantModifier =
+            modifiers.length === 0
+                ? ''
+                : modifiers.length === 1
+                  ? modifiers[0]!
+                  : sortModifiers(modifiers).join(':')
 
         const modifierId = hasImportantModifier
             ? variantModifier + IMPORTANT_MODIFIER

src/lib/sort-modifiers.ts

@@ -15,9 +15,6 @@ export const createSortModifiers = (config: AnyConfig) => {
     })
 
     return (modifiers: readonly string[]): string[] => {
-        // Fast path for common cases
-        if (modifiers.length <= 1) return [...modifiers]
-
         const result: string[] = []
         let currentSegment: string[] = []
 
@@ -32,7 +29,7 @@ export const createSortModifiers = (config: AnyConfig) => {
             if (isArbitrary || isOrderSensitive) {
                 // Sort and flush current segment alphabetically
                 if (currentSegment.length > 0) {
-                    currentSegment.sort((a, b) => a.localeCompare(b))
+                    currentSegment.sort()
                     result.push(...currentSegment)
                     currentSegment = []
                 }
@@ -45,7 +42,7 @@ export const createSortModifiers = (config: AnyConfig) => {
 
         // Sort and add any remaining segment items
         if (currentSegment.length > 0) {
-            currentSegment.sort((a, b) => a.localeCompare(b))
+            currentSegment.sort()
             result.push(...currentSegment)
         }
 

tests/tw-merge.benchmark.ts

@@ -4,6 +4,23 @@ import { extendTailwindMerge } from '../src'
 
 import testDataCollection from './tw-merge-benchmark-data.json'
 
+// Create a long class list with many conflicts (padding, margin, width, height, etc.)
+const ultraLongClassList: string[] = []
+for (let i = 0; i < 200; i++) {
+    // Add padding classes that conflict
+    ultraLongClassList.push(`p-${i % 20}`, `px-${i % 20}`, `py-${i % 20}`)
+    // Add margin classes that conflict
+    ultraLongClassList.push(`m-${i % 20}`, `mx-${i % 20}`, `my-${i % 20}`)
+    // Add width/height classes that conflict
+    ultraLongClassList.push(`w-${i % 20}`, `h-${i % 20}`)
+    // Add some non-conflicting classes
+    ultraLongClassList.push(`text-${i % 10}`, `bg-${i % 10}`)
+    // Add some with modifiers
+    if (i % 10 === 0) {
+        ultraLongClassList.push(`hover:p-${i % 20}`, `focus:m-${i % 20}`)
+    }
+}
+
 describe('twMerge', () => {
     benchWithMemory('init', () => {
         const twMerge = extendTailwindMerge({})
@@ -49,6 +66,18 @@ describe('twMerge', () => {
             twMerge(...(testDataCollection[index] as TestDataItem))
         }
     })
+
+    benchWithMemory('ultra long class list with many conflicts without cache', () => {
+        const twMerge = extendTailwindMerge({ cacheSize: 0 })
+
+        twMerge(...ultraLongClassList)
+    })
+
+    benchWithMemory('ultra long class list with many conflicts with cache', () => {
+        const twMerge = extendTailwindMerge({})
+
+        twMerge(...ultraLongClassList)
+    })
 })
 
 afterAll(() => {