Faster null checks

src/System.Private.CoreLib/Common/System/SR.cs

@@ -39,7 +39,7 @@ internal static string GetResourceString(string resourceKey, string defaultStrin
             try { resourceString = InternalGetResourceString(resourceKey); }
             catch (MissingManifestResourceException) { }
 
-            if (defaultString != null && resourceKey.Equals(resourceString, StringComparison.Ordinal))
+            if (!(defaultString is null) && resourceKey.Equals(resourceString, StringComparison.Ordinal))
             {
                 return defaultString;
             }
@@ -54,7 +54,7 @@ internal static string GetResourceString(string resourceKey, string defaultStrin
 
         private static string InternalGetResourceString(string key)
         {
-            if (key == null || key.Length == 0)
+            if (key is null || key.Length == 0)
             {
                 Debug.Fail("SR::GetResourceString with null or empty key.  Bug in caller, or weird recursive loading problem?");
                 return key;
@@ -86,7 +86,7 @@ private static string InternalGetResourceString(string key)
 
                 // Are we recursively looking up the same resource?  Note - our backout code will set
                 // the ResourceHelper's currentlyLoading stack to null if an exception occurs.
-                if (_currentlyLoading != null && _currentlyLoading.Count > 0 && _currentlyLoading.LastIndexOf(key) != -1)
+                if (!(_currentlyLoading is null) && _currentlyLoading.Count > 0 && _currentlyLoading.LastIndexOf(key) != -1)
                 {
                     // We can start infinitely recursing for one resource lookup,
                     // then during our failure reporting, start infinitely recursing again.
@@ -102,7 +102,7 @@ private static string InternalGetResourceString(string key)
                     string message = $"Infinite recursion during resource lookup within {System.CoreLib.Name}.  This may be a bug in {System.CoreLib.Name}, or potentially in certain extensibility points such as assembly resolve events or CultureInfo names.  Resource name: {key}";
                     Environment.FailFast(message);
                 }
-                if (_currentlyLoading == null)
+                if (_currentlyLoading is null)
                     _currentlyLoading = new List<string>();
 
                 // Call class constructors preemptively, so that we cannot get into an infinite
@@ -120,7 +120,7 @@ private static string InternalGetResourceString(string key)
 
                 _currentlyLoading.Add(key); // Push
 
-                if (ResourceManager == null)
+                if (ResourceManager is null)
                 {
                     ResourceManager = new ResourceManager(SR.ResourceType);
                 }
@@ -151,7 +151,7 @@ private static string InternalGetResourceString(string key)
 
         internal static string Format(string resourceFormat, params object[] args)
         {
-            if (args != null)
+            if (!(args is null))
             {
                 if (UsingResourceKeys())
                 {

src/System.Private.CoreLib/shared/Internal/IO/File.cs

@@ -23,7 +23,7 @@ public static bool Exists(string path)
         {
             try
             {
-                if (path == null)
+                if (path is null)
                     return false;
                 if (path.Length == 0)
                     return false;

src/System.Private.CoreLib/shared/Internal/Win32/RegistryKey.cs

@@ -37,7 +37,7 @@ private RegistryKey(SafeRegistryHandle hkey)
 
         void IDisposable.Dispose()
         {
-            if (_hkey != null)
+            if (!(_hkey is null))
             {
                 _hkey.Dispose();
             }
@@ -207,7 +207,7 @@ public unsafe string[] GetValueNames()
             }
             finally
             {
-                if (name != null)
+                if (!(name is null))
                     ArrayPool<char>.Shared.Return(name);
             }
 
@@ -410,7 +410,7 @@ public object GetValue(string name, object defaultValue)
                             }
                             cur = nextNull + 1;
 
-                            if (toAdd != null)
+                            if (!(toAdd is null))
                             {
                                 if (strings.Length == stringsCount)
                                 {
@@ -436,10 +436,10 @@ public object GetValue(string name, object defaultValue)
         // so this is a cut-down version that supports on that.
         internal void SetValue(string name, string value)
         {
-            if (value == null)
+            if (value is null)
                 throw new ArgumentNullException(nameof(value));
 
-            if (name != null && name.Length > MaxValueLength)
+            if (!(name is null) && name.Length > MaxValueLength)
                 throw new ArgumentException(SR.Arg_RegValStrLenBug, nameof(name));
 
             int ret = Interop.Advapi32.RegSetValueEx(_hkey,
@@ -460,7 +460,7 @@ internal void Win32Error(int errorCode, string str)
             switch (errorCode)
             {
                 case Interop.Errors.ERROR_ACCESS_DENIED:
-                    if (str != null)
+                    if (!(str is null))
                         throw new UnauthorizedAccessException(SR.Format(SR.UnauthorizedAccess_RegistryKeyGeneric_Key, str));
                     else
                         throw new UnauthorizedAccessException();

src/System.Private.CoreLib/shared/Interop/Unix/Interop.IOErrors.cs

@@ -15,7 +15,7 @@ private static void ThrowExceptionForIoErrno(ErrorInfo errorInfo, string path, b
         Debug.Assert(errorInfo.Error != Error.SUCCESS);
         Debug.Assert(errorInfo.Error != Error.EINTR, "EINTR errors should be handled by the native shim and never bubble up to managed code");
 
-        if (errorRewriter != null)
+        if (!(errorRewriter is null))
         {
             errorInfo = errorRewriter(errorInfo);
         }

src/System.Private.CoreLib/shared/Interop/Unix/System.Native/Interop.GetCwd.cs

@@ -20,7 +20,7 @@ internal static unsafe string GetCwd()
             // First try to get the path into a buffer on the stack
             byte* stackBuf = stackalloc byte[StackLimit];
             string result = GetCwdHelper(stackBuf, StackLimit);
-            if (result != null)
+            if (!(result is null))
             {
                 return result;
             }
@@ -36,7 +36,7 @@ internal static unsafe string GetCwd()
                     fixed (byte* ptr = &buf[0])
                     {
                         result = GetCwdHelper(ptr, buf.Length);
-                        if (result != null)
+                        if (!(result is null))
                         {
                             return result;
                         }

src/System.Private.CoreLib/shared/System/AggregateException.cs

@@ -58,7 +58,7 @@ public AggregateException(string message)
         public AggregateException(string message, Exception innerException)
             : base(message, innerException)
         {
-            if (innerException == null)
+            if (innerException is null)
             {
                 throw new ArgumentNullException(nameof(innerException));
             }
@@ -107,7 +107,7 @@ public AggregateException(params Exception[] innerExceptions) :
         public AggregateException(string message, IEnumerable<Exception> innerExceptions)
             // If it's already an IList, pass that along (a defensive copy will be made in the delegated ctor).  If it's null, just pass along
             // null typed correctly.  Otherwise, create an IList from the enumerable and pass that along. 
-            : this(message, innerExceptions as IList<Exception> ?? (innerExceptions == null ? (List<Exception>)null : new List<Exception>(innerExceptions)))
+            : this(message, innerExceptions as IList<Exception> ?? (innerExceptions is null ? (List<Exception>)null : new List<Exception>(innerExceptions)))
         {
         }
 
@@ -136,9 +136,9 @@ public AggregateException(string message, params Exception[] innerExceptions) :
         /// <exception cref="T:System.ArgumentException">An element of <paramref name="innerExceptions"/> is
         /// null.</exception>
         private AggregateException(string message, IList<Exception> innerExceptions)
-            : base(message, innerExceptions != null && innerExceptions.Count > 0 ? innerExceptions[0] : null)
+            : base(message, !(innerExceptions is null) && innerExceptions.Count > 0 ? innerExceptions[0] : null)
         {
-            if (innerExceptions == null)
+            if (innerExceptions is null)
             {
                 throw new ArgumentNullException(nameof(innerExceptions));
             }
@@ -194,7 +194,7 @@ internal AggregateException(string message, IEnumerable<ExceptionDispatchInfo> i
             // If it's already an IList, pass that along (a defensive copy will be made in the delegated ctor).  If it's null, just pass along
             // null typed correctly.  Otherwise, create an IList from the enumerable and pass that along. 
             : this(message, innerExceptionInfos as IList<ExceptionDispatchInfo> ??
-                                (innerExceptionInfos == null ?
+                                (innerExceptionInfos is null ?
                                     (List<ExceptionDispatchInfo>)null :
                                     new List<ExceptionDispatchInfo>(innerExceptionInfos)))
         {
@@ -213,10 +213,10 @@ internal AggregateException(string message, IEnumerable<ExceptionDispatchInfo> i
         /// <exception cref="T:System.ArgumentException">An element of <paramref name="innerExceptionInfos"/> is
         /// null.</exception>
         private AggregateException(string message, IList<ExceptionDispatchInfo> innerExceptionInfos)
-            : base(message, innerExceptionInfos != null && innerExceptionInfos.Count > 0 && innerExceptionInfos[0] != null ?
+            : base(message, !(innerExceptionInfos is null) && innerExceptionInfos.Count > 0 && innerExceptionInfos[0] != null ?
                                 innerExceptionInfos[0].SourceException : null)
         {
-            if (innerExceptionInfos == null)
+            if (innerExceptionInfos is null)
             {
                 throw new ArgumentNullException(nameof(innerExceptionInfos));
             }
@@ -229,7 +229,7 @@ private AggregateException(string message, IList<ExceptionDispatchInfo> innerExc
             for (int i = 0; i < exceptionsCopy.Length; i++)
             {
                 var edi = innerExceptionInfos[i];
-                if (edi != null) exceptionsCopy[i] = edi.SourceException;
+                if (!(edi is null)) exceptionsCopy[i] = edi.SourceException;
 
                 if (exceptionsCopy[i] == null)
                 {
@@ -252,13 +252,13 @@ private AggregateException(string message, IList<ExceptionDispatchInfo> innerExc
         protected AggregateException(SerializationInfo info, StreamingContext context) :
             base(info, context)
         {
-            if (info == null)
+            if (info is null)
             {
                 throw new ArgumentNullException(nameof(info));
             }
 
             Exception[] innerExceptions = info.GetValue("InnerExceptions", typeof(Exception[])) as Exception[];
-            if (innerExceptions == null)
+            if (innerExceptions is null)
             {
                 throw new SerializationException(SR.AggregateException_DeserializationFailure);
             }
@@ -294,7 +294,7 @@ public override Exception GetBaseException()
             // Recursively traverse the inner exceptions as long as the inner exception of type AggregateException and has only one inner exception
             Exception back = this;
             AggregateException backAsAggregate = this;
-            while (backAsAggregate != null && backAsAggregate.InnerExceptions.Count == 1)
+            while (!(backAsAggregate is null) && backAsAggregate.InnerExceptions.Count == 1)
             {
                 back = back.InnerException;
                 backAsAggregate = back as AggregateException;
@@ -333,7 +333,7 @@ public ReadOnlyCollection<Exception> InnerExceptions
         /// null.</exception>
         public void Handle(Func<Exception, bool> predicate)
         {
-            if (predicate == null)
+            if (predicate is null)
             {
                 throw new ArgumentNullException(nameof(predicate));
             }
@@ -345,7 +345,7 @@ public void Handle(Func<Exception, bool> predicate)
                 // exceptions (to be rethrown later) and add it.
                 if (!predicate(m_innerExceptions[i]))
                 {
-                    if (unhandledExceptions == null)
+                    if (unhandledExceptions is null)
                     {
                         unhandledExceptions = new List<Exception>();
                     }
@@ -355,7 +355,7 @@ public void Handle(Func<Exception, bool> predicate)
             }
 
             // If there are unhandled exceptions remaining, throw them.
-            if (unhandledExceptions != null)
+            if (!(unhandledExceptions is null))
             {
                 throw new AggregateException(Message, unhandledExceptions);
             }
@@ -394,7 +394,7 @@ public AggregateException Flatten()
                 {
                     Exception currentInnerException = currentInnerExceptions[i];
 
-                    if (currentInnerException == null)
+                    if (currentInnerException is null)
                     {
                         continue;
                     }
@@ -403,7 +403,7 @@ public AggregateException Flatten()
 
                     // If this exception is an aggregate, keep it around for later.  Otherwise,
                     // simply add it to the list of flattened exceptions to be returned.
-                    if (currentInnerAsAggregate != null)
+                    if (!(currentInnerAsAggregate is null))
                     {
                         exceptionsToFlatten.Add(currentInnerAsAggregate);
                     }

src/System.Private.CoreLib/shared/System/ArgumentOutOfRangeException.cs

@@ -77,10 +77,10 @@ public override string Message
             get
             {
                 string s = base.Message;
-                if (_actualValue != null)
+                if (!(_actualValue is null))
                 {
                     string valueMessage = SR.Format(SR.ArgumentOutOfRange_ActualValue, _actualValue.ToString());
-                    if (s == null)
+                    if (s is null)
                         return valueMessage;
                     return s + Environment.NewLine + valueMessage;
                 }

src/System.Private.CoreLib/shared/System/ArraySegment.cs

@@ -38,7 +38,7 @@ namespace System
 
         public ArraySegment(T[] array)
         {
-            if (array == null)
+            if (array is null)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.array);
 
             _array = array;
@@ -51,7 +51,7 @@ public ArraySegment(T[] array, int offset, int count)
             // Validate arguments, check is minimal instructions with reduced branching for inlinable fast-path
             // Negative values discovered though conversion to high values when converted to unsigned
             // Failure should be rare and location determination and message is delegated to failure functions
-            if (array == null || (uint)offset > (uint)array.Length || (uint)count > (uint)(array.Length - offset))
+            if (array is null || (uint)offset > (uint)array.Length || (uint)count > (uint)(array.Length - offset))
                 ThrowHelper.ThrowArraySegmentCtorValidationFailedExceptions(array, offset, count);
 
             _array = array;
@@ -95,7 +95,7 @@ public Enumerator GetEnumerator()
 
         public override int GetHashCode()
         {
-            if (_array == null)
+            if (_array is null)
             {
                 return 0;
             }
@@ -192,7 +192,7 @@ public T[] ToArray()
             return !(a == b);
         }
 
-        public static implicit operator ArraySegment<T>(T[] array) => array != null ? new ArraySegment<T>(array) : default;
+        public static implicit operator ArraySegment<T>(T[] array) => !(array is null) ? new ArraySegment<T>(array) : default;
 
         #region IList<T>
         T IList<T>.this[int index]
@@ -305,7 +305,7 @@ bool ICollection<T>.Remove(T item)
 
         private void ThrowInvalidOperationIfDefault()
         {
-            if (_array == null)
+            if (_array is null)
             {
                 ThrowHelper.ThrowInvalidOperationException(ExceptionResource.InvalidOperation_NullArray);
             }

src/System.Private.CoreLib/shared/System/BadImageFormatException.cs

@@ -80,9 +80,9 @@ public override string Message
 
         private void SetMessageField()
         {
-            if (_message == null)
+            if (_message is null)
             {
-                if ((_fileName == null) &&
+                if ((_fileName is null) &&
                     (HResult == HResults.COR_E_EXCEPTION))
                     _message = SR.Arg_BadImageFormatException;
 
@@ -100,18 +100,18 @@ public override string ToString()
         {
             string s = GetType().ToString() + ": " + Message;
 
-            if (_fileName != null && _fileName.Length != 0)
+            if (!(_fileName is null) && _fileName.Length != 0)
                 s += Environment.NewLine + SR.Format(SR.IO_FileName_Name, _fileName);
 
-            if (InnerException != null)
+            if (!(InnerException is null))
                 s = s + " ---> " + InnerException.ToString();
 
-            if (StackTrace != null)
+            if (!(StackTrace is null))
                 s += Environment.NewLine + StackTrace;
 
-            if (_fusionLog != null)
+            if (!(_fusionLog is null))
             {
-                if (s == null)
+                if (s is null)
                     s = " ";
                 s += Environment.NewLine;
                 s += Environment.NewLine;