path: fix POSIX path.resolve() perf regression

lib/path.js

@@ -23,7 +23,6 @@
 
 const {
   FunctionPrototypeBind,
-  RegExp,
   StringPrototypeCharCodeAt,
   StringPrototypeIndexOf,
   StringPrototypeLastIndexOf,
@@ -48,6 +47,8 @@ const {
   validateString,
 } = require('internal/validators');
 
+const platformIsWin32 = (process.platform === 'win32');
+
 function isPathSeparator(code) {
   return code === CHAR_FORWARD_SLASH || code === CHAR_BACKWARD_SLASH;
 }
@@ -1011,24 +1012,29 @@ const win32 = {
   posix: null
 };
 
+const posixCwd = (() => {
+  if (platformIsWin32) {
+    // Converts Windows' backslash path separators to POSIX forward slashes
+    // and truncates any drive indicator
+    const regexp = /\\/g;
+    return () => {
+      const cwd = StringPrototypeReplace(process.cwd(), regexp, '/');
+      return StringPrototypeSlice(cwd, StringPrototypeIndexOf(cwd, '/'));
+    };
+  }
+
+  // We're already on POSIX, no need for any transformations
+  return () => process.cwd();
+})();
+
 const posix = {
   // path.resolve([from ...], to)
   resolve(...args) {
     let resolvedPath = '';
     let resolvedAbsolute = false;
 
     for (let i = args.length - 1; i >= -1 && !resolvedAbsolute; i--) {
-      let path;
-      if (i >= 0) {
-        path = args[i];
-      } else {
-        const _ = StringPrototypeReplace(
-          process.cwd(),
-          new RegExp(`\\${module.exports.sep}`, 'g'),
-          posix.sep
-        );
-        path = StringPrototypeSlice(_, StringPrototypeIndexOf(_, posix.sep));
-      }
+      const path = i >= 0 ? args[i] : posixCwd();
 
       validateString(path, 'path');
 
@@ -1431,4 +1437,4 @@ posix.posix = win32.posix = posix;
 win32._makeLong = win32.toNamespacedPath;
 posix._makeLong = posix.toNamespacedPath;
 
-module.exports = process.platform === 'win32' ? win32 : posix;
+module.exports = platformIsWin32 ? win32 : posix;