HeapAllocationViewer for Rider and ReSharper

This plugin statically analyzes C# code to find all local object allocations happening.

It can be used to reduce number of heap allocations in hot paths of your C# program.

Features

• It can detect and visualize all boxing cases, including:

  struct Boxing {
  void M(string a) {
  object obj = 42;                // implicit conversion Int32 ~> Object
  string path = a + '/' + obj;    // implicit conversion Char ~> Object
  int code = this.GetHashCode();  // non-overriden virtual method call on struct
  string caseA = E.A.ToString();  // the same, virtual call
  IComparable comparable = E.A;   // valuetype conversion to interface type
  Action<string> action = this.M; // delegate from value type method
  Type type = this.GetType();     // GetType() call is always virtual
  }
  
  enum E { A, B, C }
  }

• It can visualize some hidden allocations happening in C#, including:

  class HeapAllocations {
  List<int> _xs = new List<int>();  // explicit object creation expressions
  int[] _ys = {1, 2, 3};            // allocation via array initializer syntax
  
  void M(params string[] args) {
  string c = args[0] + "/";       // string concatenation
  M("abc", "def");                // parameters array allocation
  M();                            // the same, hidden 'new string[0]'
  var xs = Enumerable.Range(0,1); // iterator method call
  var ys = from x in xs
           let y = x + 1          // anonymous type creation for 'let'
           select x + y;
  }
  
  void N(List<string> xs) {
  foreach (var s in xs) F(s);     // no allocations, value type enumerator
  
  IEnumerable<string> ys = xs;
  foreach (var s in ys) F(s);     // IEnumerator allocation in foreach
  }
  }

• It can detect delegate instances allocation, ignoring cached delegates:

  class Delegates {
  static void M(string s) {
  Action<string> method = M;      // non-cached delegate from method group
  Action lambda = () => M("a");   // cached delegate from static lambda
  Action closure = () => M(s);    // non-cached lambda with closure 's'
  }
  
  void M<T>() {
  Action generic = () => { };     // non-cached, lambda in generic method
  Action closure = () => M<T>();  // non-cached, captures 'this' to closure
  }
  }

• It can detect closure ("display classes") creation points:

  class Closures {
  IEnumerable<string> StupidExample(string str) {
  // <= hidden closure class allocation happens here
  if (str == null)
    return Enumerable.Empty<string>();
  
  if (str.Length == 0) {
    return Enumerable.Empty<string>();
  } else {
    // <= second hidden closure allocation (nested closure)
    int value = str.Count(x => x == '_');
  
    return Enumerable
      .Range(0, str.Length)
      .Select(count => // delegate instance allocation
        str.Substring(Math.Max(value, count)));
  }
  }
  }

Notes

• Please, avoid premature optimizations. Use this tool with care, only when it matters to reduce allocations count;
• You can change default colors of highlightings in Visual Studio settings: go Tools - Settings - Fonts and colors and check colors for items "ReSharper HeapView Boxing" and "ReSharper HeapView Allocation";
• You can change highlighting severity or search for all issues in project/solution as usual - via Alt+Enter menu over highlighting;
• This plugin highly relies on Microsoft's implementation of C# compiler shipping with VS, it may produce false positives for other C# implementations like Mono C# compiler;
• Plugin's changelog is here.