Optimize NativeAOT delegate field layout

src/coreclr/nativeaot/System.Private.CoreLib/src/System/Delegate.cs

@@ -41,12 +41,10 @@ protected Delegate([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.Al
             throw new PlatformNotSupportedException();
         }
 
-        // New Delegate Implementation
-
-        private object _firstParameter;
         private object _helperObject;
-        private nint _extraFunctionPointerOrData;
+        private object _firstParameter; // Keep _firstParameter and _functionPointer next to each other for optimal delegate invoke performance
         private IntPtr _functionPointer;
+        private nint _extraFunctionPointerOrData;
 
         // _helperObject may point to an array of delegates if this is a multicast delegate. We use this wrapper to distinguish between
         // our own array of delegates and user provided Wrapper[]. As a added benefit, this wrapper also eliminates array co-variance

src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs

@@ -3451,8 +3451,13 @@ private void getEEInfo(ref CORINFO_EE_INFO pEEInfoOut)
 
             pEEInfoOut.inlinedCallFrameInfo.size = (uint)SizeOfPInvokeTransitionFrame;
 
-            pEEInfoOut.offsetOfDelegateInstance = (uint)pointerSize;            // Delegate::_firstParameter
-            pEEInfoOut.offsetOfDelegateFirstTarget = OffsetOfDelegateFirstTarget;
+#if READYTORUN
+            pEEInfoOut.offsetOfDelegateInstance = (uint)pointerSize; // Delegate._target
+            pEEInfoOut.offsetOfDelegateFirstTarget = 3 * (uint)pointerSize; // Delegate._methodPtr
+#else            
+            pEEInfoOut.offsetOfDelegateInstance = 2 * (uint)pointerSize; // Delegate._firstParameter
+            pEEInfoOut.offsetOfDelegateFirstTarget = 3 * (uint)pointerSize; // Delegate._functionPointer
+#endif
 
             pEEInfoOut.sizeOfReversePInvokeFrame = (uint)SizeOfReversePInvokeTransitionFrame;
 

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/TypePreinit.cs

@@ -3295,34 +3295,34 @@ public void WriteContent(ref ObjectDataBuilder builder, ISymbolNode thisNode, No
                 {
                     Debug.Assert(creationInfo.Constructor.Method.Name == "InitializeOpenStaticThunk"u8);
 
-                    // _firstParameter
-                    builder.EmitPointerReloc(thisNode);
-
                     // _helperObject
                     builder.EmitZeroPointer();
 
-                    // _extraFunctionPointerOrData
-                    builder.EmitPointerReloc(creationInfo.GetTargetNode(factory));
+                    // _firstParameter
+                    builder.EmitPointerReloc(thisNode);
 
                     // _functionPointer
                     Debug.Assert(creationInfo.Thunk != null);
                     builder.EmitPointerReloc(creationInfo.Thunk);
+
+                    // _extraFunctionPointerOrData
+                    builder.EmitPointerReloc(creationInfo.GetTargetNode(factory));
                 }
                 else
                 {
                     Debug.Assert(creationInfo.Constructor.Method.Name == "InitializeClosedInstance"u8);
 
-                    // _firstParameter
-                    _firstParameter.WriteFieldData(ref builder, factory);
-
                     // _helperObject
                     builder.EmitZeroPointer();
 
-                    // _extraFunctionPointerOrData
-                    builder.EmitZeroPointer();
+                    // _firstParameter
+                    _firstParameter.WriteFieldData(ref builder, factory);
 
                     // _functionPointer
                     builder.EmitPointerReloc(creationInfo.GetTargetNode(factory));
+
+                    // _extraFunctionPointerOrData
+                    builder.EmitZeroPointer();
                 }
             }
 

src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs

@@ -477,8 +477,6 @@ unsafe partial class CorInfoImpl
     {
         private const CORINFO_RUNTIME_ABI TargetABI = CORINFO_RUNTIME_ABI.CORINFO_CORECLR_ABI;
 
-        private uint OffsetOfDelegateFirstTarget => (uint)(3 * PointerSize); // Delegate._methodPtr
-
         private readonly ReadyToRunCodegenCompilation _compilation;
         private MethodWithGCInfo _methodCodeNode;
         private MethodColdCodeNode _methodColdCodeNode;

src/coreclr/tools/aot/ILCompiler.RyuJit/JitInterface/CorInfoImpl.RyuJit.cs

@@ -29,7 +29,6 @@ internal unsafe partial class CorInfoImpl
     {
         private const CORINFO_RUNTIME_ABI TargetABI = CORINFO_RUNTIME_ABI.CORINFO_NATIVEAOT_ABI;
 
-        private uint OffsetOfDelegateFirstTarget => (uint)(4 * PointerSize); // Delegate._functionPointer
         private int SizeOfReversePInvokeTransitionFrame => 2 * PointerSize;
 
         private RyuJitCompilation _compilation;