Remove ILLink support for field init substitutions (#107380)

The implementation of this was attempting to rewrite the cctor in a way
that was not robust.

Author: sbomer

docs/tools/illink/data-formats.md

@@ -253,20 +253,6 @@ Entire method body is replaces with `throw` instruction when method is reference
 </linker>
 ```
 
-### Override static field value with a constant
-
-The `initialize` attribute is optional and when not specified the code to set the static field to the value will not be generated.
-
-```xml
-<linker>
-  <assembly fullname="Assembly">
-    <type fullname="Assembly.A">
-      <field name="MyNumericField" value="5" initialize="true" />
-    </type>
-  </assembly>
-</linker>
-```
-
 ### Remove embedded resources
 
 ```xml

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

@@ -144,12 +144,8 @@ protected override void ProcessField(TypeDesc type, XPathNavigator fieldNav)
 
             if (string.Equals(GetAttribute(fieldNav, "initialize"), "true", StringComparison.InvariantCultureIgnoreCase))
             {
-                // We would need to also mess with the cctor of the type to set the field to this value:
-                //
-                // * ILLink will remove all stsfld instructions referencing this field from the cctor
-                // * It will place an explicit stsfld in front of the last "ret" instruction in the cctor
-                //
-                // This approach... has issues.
+                // We would need to also mess with the cctor of the type to set the field to this value,
+                // and doing so correctly is difficult.
                 throw new NotSupportedException();
             }
 

src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Substitutions.Shared.xml

@@ -20,7 +20,7 @@
       <method signature="System.Boolean InitializeBinaryFormatter()" body="stub" value="false" feature="System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization" featurevalue="false" />
     </type>
     <type fullname="System.Threading.Tasks.Task" feature="System.Diagnostics.Debugger.IsSupported" featurevalue="false">
-      <field name="s_asyncDebuggingEnabled" value="false" initialize="false" />
+      <field name="s_asyncDebuggingEnabled" value="false" />
     </type>
   </assembly>
 </linker>

src/tools/illink/src/linker/CompatibilitySuppressions.xml

@@ -745,14 +745,6 @@
     <DiagnosticId>CP0002</DiagnosticId>
     <Target>M:Mono.Linker.AnnotationStore.HasPreservedStaticCtor(Mono.Cecil.TypeDefinition)</Target>
   </Suppression>
-  <Suppression>
-    <DiagnosticId>CP0002</DiagnosticId>
-    <Target>M:Mono.Linker.AnnotationStore.HasSubstitutedInit(Mono.Cecil.FieldDefinition)</Target>
-  </Suppression>
-  <Suppression>
-    <DiagnosticId>CP0002</DiagnosticId>
-    <Target>M:Mono.Linker.AnnotationStore.HasSubstitutedInit(Mono.Cecil.TypeDefinition)</Target>
-  </Suppression>
   <Suppression>
     <DiagnosticId>CP0002</DiagnosticId>
     <Target>M:Mono.Linker.AnnotationStore.IsIndirectlyCalled(Mono.Cecil.MethodDefinition)</Target>

src/tools/illink/src/linker/Linker.Steps/BodySubstitutionParser.cs

@@ -117,7 +117,9 @@ protected override void ProcessField (TypeDefinition type, XPathNavigator fieldN
 
 			string init = GetAttribute (fieldNav, "initialize");
 			if (init?.ToLowerInvariant () == "true") {
-				_substitutionInfo.SetFieldInit (field);
+				// We would need to also mess with the cctor of the type to set the field to this value,
+				// and doing so correctly is difficult.
+				throw new NotSupportedException ();
 			}
 		}
 

src/tools/illink/src/linker/Linker.Steps/CodeRewriterStep.cs

@@ -37,68 +37,10 @@ void ProcessType (TypeDefinition type)
 					ProcessMethod (method);
 			}
 
-			if (type.HasFields && Annotations.HasSubstitutedInit (type)) {
-				AddFieldsInitializations (type);
-			}
-
 			foreach (var nested in type.NestedTypes)
 				ProcessType (nested);
 		}
 
-		void AddFieldsInitializations (TypeDefinition type)
-		{
-			Instruction ret;
-			LinkerILProcessor processor;
-
-			var cctor = type.Methods.FirstOrDefault (MethodDefinitionExtensions.IsStaticConstructor);
-			if (cctor == null) {
-				type.Attributes |= TypeAttributes.BeforeFieldInit;
-
-				var method = new MethodDefinition (".cctor",
-					MethodAttributes.Static | MethodAttributes.Private | MethodAttributes.SpecialName | MethodAttributes.RTSpecialName | MethodAttributes.HideBySig,
-					Assembly.MainModule.TypeSystem.Void);
-
-				type.Methods.Add (method);
-
-				processor = method.Body.GetLinkerILProcessor ();
-				ret = Instruction.Create (OpCodes.Ret);
-				processor.Append (ret);
-			} else {
-				var body = cctor.Body;
-#pragma warning disable RS0030 // After MarkStep all methods should be processed and thus accessing Cecil directly is the right approach
-				var instructions = body.Instructions;
-#pragma warning restore RS0030
-				ret = instructions.Last (l => l.OpCode.Code == Code.Ret);
-				processor = body.GetLinkerILProcessor ();
-
-				for (int i = 0; i < instructions.Count; ++i) {
-					var instr = instructions[i];
-					if (instr.OpCode.Code != Code.Stsfld)
-						continue;
-
-					var field = (FieldReference) instr.Operand;
-					if (!Annotations.HasSubstitutedInit (field.Resolve ()))
-						continue;
-
-					processor.Replace (instr, Instruction.Create (OpCodes.Pop));
-				}
-			}
-
-			foreach (var field in type.Fields) {
-				if (!Annotations.HasSubstitutedInit (field))
-					continue;
-
-				Context.Annotations.TryGetFieldUserValue (field, out object? value);
-
-				var valueInstr = CreateConstantResultInstruction (Context, field.FieldType, value);
-				if (valueInstr == null)
-					throw new NotImplementedException (field.FieldType.ToString ());
-
-				processor.InsertBefore (ret, valueInstr);
-				processor.InsertBefore (ret, Instruction.Create (OpCodes.Stsfld, field));
-			}
-		}
-
 		void ProcessMethod (MethodDefinition method)
 		{
 			switch (Annotations.GetAction (method)) {

src/tools/illink/src/linker/Linker.Steps/MarkStep.cs

@@ -1712,11 +1712,6 @@ void MarkField (FieldDefinition field, in DependencyInfo reason, in MessageOrigi
 				};
 				MarkStaticConstructor (parent, cctorReason, fieldOrigin);
 			}
-
-			if (Annotations.HasSubstitutedInit (field)) {
-				Annotations.SetPreservedStaticCtor (parent);
-				Annotations.SetSubstitutedInit (parent);
-			}
 		}
 
 		void ProcessAnalysisAnnotationsForField (FieldDefinition field, DependencyKind dependencyKind, in MessageOrigin origin)

src/tools/illink/src/linker/Linker/Annotations.cs

@@ -147,21 +147,6 @@ public void SetStubValue (MethodDefinition method, object value)
 			MemberActions.PrimarySubstitutionInfo.SetMethodStubValue (method, value);
 		}
 
-		public bool HasSubstitutedInit (FieldDefinition field)
-		{
-			return MemberActions.HasSubstitutedInit (field);
-		}
-
-		public void SetSubstitutedInit (TypeDefinition type)
-		{
-			fieldType_init.Add (type);
-		}
-
-		public bool HasSubstitutedInit (TypeDefinition type)
-		{
-			return fieldType_init.Contains (type);
-		}
-
 		[Obsolete ("Mark token providers with a reason instead.")]
 		public void Mark (IMetadataTokenProvider provider)
 		{

src/tools/illink/src/linker/Linker/MemberActionStore.cs

@@ -150,16 +150,5 @@ public bool TryGetFieldUserValue (FieldDefinition field, out object? value)
 
 			return embeddedXml.FieldValues.TryGetValue (field, out value);
 		}
-
-		public bool HasSubstitutedInit (FieldDefinition field)
-		{
-			if (PrimarySubstitutionInfo.FieldInit.Contains (field))
-				return true;
-
-			if (!TryGetSubstitutionInfo (field, out var embeddedXml))
-				return false;
-
-			return embeddedXml.FieldInit.Contains (field);
-		}
 	}
 }

src/tools/illink/src/linker/Linker/SubstitutionInfo.cs

@@ -11,14 +11,12 @@ public class SubstitutionInfo
 		public Dictionary<MethodDefinition, MethodAction> MethodActions { get; }
 		public Dictionary<MethodDefinition, object?> MethodStubValues { get; }
 		public Dictionary<FieldDefinition, object?> FieldValues { get; }
-		public HashSet<FieldDefinition> FieldInit { get; }
 
 		public SubstitutionInfo ()
 		{
 			MethodActions = new Dictionary<MethodDefinition, MethodAction> ();
 			MethodStubValues = new Dictionary<MethodDefinition, object?> ();
 			FieldValues = new Dictionary<FieldDefinition, object?> ();
-			FieldInit = new HashSet<FieldDefinition> ();
 		}
 
 		public void SetMethodAction (MethodDefinition method, MethodAction action)
@@ -35,10 +33,5 @@ public void SetFieldValue (FieldDefinition field, object? value)
 		{
 			FieldValues[field] = value;
 		}
-
-		public void SetFieldInit (FieldDefinition field)
-		{
-			FieldInit.Add (field);
-		}
 	}
 }