Place read-only non-GC static bases into read-only section (#114477)

If all fields that contribute to the base are effectively read only, place the base into read-only section.

This only takes effect if data dehydration is turned off.

Author: MichalStrehovsky

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/NonGCStaticsNode.cs

@@ -34,12 +34,36 @@ public NonGCStaticsNode(MetadataType type, PreinitializationManager preinitializ
 
         protected override ObjectNodeSection GetDehydratedSection(NodeFactory factory)
         {
-            if (HasCCtorContext
-                || _preinitializationManager.IsPreinitialized(_type))
+            if (HasCCtorContext)
             {
-                // We have data to be emitted so this needs to be in an initialized data section
+                // Needs to be writable initialized section because we need info on how to run cctor and whether it ran.
                 return ObjectNodeSection.DataSection;
             }
+            else if (_preinitializationManager.IsPreinitialized(_type))
+            {
+                // Unix linkers don't like relocs to readonly data section
+                if (!factory.Target.IsWindows)
+                    return ObjectNodeSection.DataSection;
+
+                ReadOnlyFieldPolicy readOnlyPolicy = _preinitializationManager.ReadOnlyFieldPolicy;
+
+                bool allFieldsReadOnly = true;
+                foreach (FieldDesc field in _type.GetFields())
+                {
+                    if (!IsNonGcStaticField(field))
+                        continue;
+
+                    allFieldsReadOnly = readOnlyPolicy.IsReadOnly(field);
+                    if (!allFieldsReadOnly)
+                        break;
+                }
+
+                // If all fields are read only, we can place this into a read only section
+                if (allFieldsReadOnly)
+                    return ObjectNodeSection.ReadOnlyDataSection;
+                else
+                    return ObjectNodeSection.DataSection;
+            }
             else
             {
                 // This is all zeros; place this to the BSS section
@@ -149,6 +173,9 @@ protected override DependencyList ComputeNonRelocationBasedDependencies(NodeFact
             return dependencyList;
         }
 
+        private static bool IsNonGcStaticField(FieldDesc field)
+            => field.IsStatic && !field.HasRva && !field.IsLiteral && !field.IsThreadStatic && !field.HasGCStaticBase;
+
         protected override ObjectData GetDehydratableData(NodeFactory factory, bool relocsOnly)
         {
             ObjectDataBuilder builder = new ObjectDataBuilder(factory, relocsOnly);
@@ -193,7 +220,7 @@ protected override ObjectData GetDehydratableData(NodeFactory factory, bool relo
                 int initialOffset = builder.CountBytes;
                 foreach (FieldDesc field in _type.GetFields())
                 {
-                    if (!field.IsStatic || field.HasRva || field.IsLiteral || field.IsThreadStatic || field.HasGCStaticBase)
+                    if (!IsNonGcStaticField(field))
                         continue;
 
                     int padding = field.Offset.AsInt - builder.CountBytes + initialOffset;

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

@@ -17,6 +17,8 @@ public class PreinitializationManager
     {
         private readonly bool _supportsLazyCctors;
 
+        public ReadOnlyFieldPolicy ReadOnlyFieldPolicy => _preinitHashTable._readOnlyPolicy;
+
         public PreinitializationManager(TypeSystemContext context, CompilationModuleGroup compilationGroup, ILProvider ilprovider, TypePreinit.TypePreinitializationPolicy policy, ReadOnlyFieldPolicy readOnlyPolicy, FlowAnnotations flowAnnotations)
         {
             _supportsLazyCctors = context.SystemModule.GetType("System.Runtime.CompilerServices", "ClassConstructorRunner", throwIfNotFound: false) != null;
@@ -139,7 +141,7 @@ private sealed class PreinitializationInfoHashtable : LockFreeReaderHashtable<Me
             private readonly CompilationModuleGroup _compilationGroup;
             private readonly ILProvider _ilProvider;
             internal readonly TypePreinit.TypePreinitializationPolicy _policy;
-            private readonly ReadOnlyFieldPolicy _readOnlyPolicy;
+            internal readonly ReadOnlyFieldPolicy _readOnlyPolicy;
             private readonly FlowAnnotations _flowAnnotations;
 
             public PreinitializationInfoHashtable(CompilationModuleGroup compilationGroup, ILProvider ilProvider, TypePreinit.TypePreinitializationPolicy policy, ReadOnlyFieldPolicy readOnlyPolicy, FlowAnnotations flowAnnotations)