Simplify ldftn reverse lookups

src/coreclr/nativeaot/System.Private.Reflection.Execution/src/Internal/Reflection/Execution/ExecutionEnvironmentImplementation.MappingTables.cs

@@ -566,74 +566,24 @@ public bool TryGetOffsetsRange(IntPtr functionPointer, out int firstParserOffset
         // ldftn reverse lookup hash. Must be cleared and reset if the module list changes. (All sets to
         // this variable must happen under a lock)
         private volatile KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>[] _ldftnReverseLookup_InvokeMap;
-        private Func<NativeFormatModuleInfo, FunctionPointersToOffsets> _computeLdFtnLookupInvokeMapInvokeMap = ComputeLdftnReverseLookup_InvokeMap;
 
         /// <summary>
-        /// Initialize a lookup array of module to function pointer/parser offset pair arrays. Do so in a manner that will allow
-        /// future work which will invalidate the cache (by setting it to null)
+        /// Initialize a lookup array of module to function pointer/parser offset pair arrays.
         /// </summary>
-        /// <param name="ldftnReverseLookupStatic">pointer to static which holds cache value. This is treated as a volatile variable</param>
-        /// <param name="lookupComputer"></param>
-        /// <returns></returns>
-        private KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>[] GetLdFtnReverseLookups_Helper(ref KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>[] ldftnReverseLookupStatic, Func<NativeFormatModuleInfo, FunctionPointersToOffsets> lookupComputer)
+        private KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>[] GetLdFtnReverseLookups_InvokeMap()
         {
-            KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>[] ldFtnReverseLookup = Volatile.Read(ref ldftnReverseLookupStatic);
-
-            if (ldFtnReverseLookup != null)
-                return ldFtnReverseLookup;
-            else
+            KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>[] ldFtnReverseLookup = _ldftnReverseLookup_InvokeMap;
+            if (ldFtnReverseLookup == null)
             {
-                lock (this)
+                var ldFtnReverseLookupBuilder = new ArrayBuilder<KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>>();
+                foreach (NativeFormatModuleInfo module in ModuleList.EnumerateModules())
                 {
-                    ldFtnReverseLookup = Volatile.Read(ref ldftnReverseLookupStatic);
-
-                    // double checked lock, safe due to use of volatile on s_ldftnReverseHashes
-                    if (ldFtnReverseLookup != null)
-                        return ldFtnReverseLookup;
-
-                    // FUTURE: add a module load callback to invalidate this cache if a new module is loaded.
-                    while (true)
-                    {
-                        int size = 0;
-                        foreach (NativeFormatModuleInfo module in ModuleList.EnumerateModules())
-                        {
-                            size++;
-                        }
-
-                        ldFtnReverseLookup = new KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>[size];
-                        int index = 0;
-                        bool restart = false;
-                        foreach (NativeFormatModuleInfo module in ModuleList.EnumerateModules())
-                        {
-                            // If the module list changes during execution of this code, rebuild from scratch
-                            if (index >= ldFtnReverseLookup.Length)
-                            {
-                                restart = true;
-                                break;
-                            }
-
-                            ldFtnReverseLookup[index] = new KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>(module, lookupComputer(module));
-                            index++;
-                        }
-
-                        if (restart)
-                            continue;
-
-                        // unless we need to repeat the module enumeration, only execute the body of this while loop once.
-                        break;
-                    }
-
-                    Volatile.Write(ref ldftnReverseLookupStatic, ldFtnReverseLookup);
-                    return ldFtnReverseLookup;
+                    ldFtnReverseLookupBuilder.Add(new KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>(module, ComputeLdftnReverseLookup_InvokeMap(module)));
                 }
+                ldFtnReverseLookup = ldFtnReverseLookupBuilder.ToArray();
+                _ldftnReverseLookup_InvokeMap = ldFtnReverseLookup;
             }
-        }
-
-        private KeyValuePair<NativeFormatModuleInfo, FunctionPointersToOffsets>[] GetLdFtnReverseLookups_InvokeMap()
-        {
-#pragma warning disable 0420 // GetLdFtnReverseLookups_Helper treats its first parameter as volatile by using explicit Volatile operations
-            return GetLdFtnReverseLookups_Helper(ref _ldftnReverseLookup_InvokeMap, _computeLdFtnLookupInvokeMapInvokeMap);
-#pragma warning restore 0420
+            return ldFtnReverseLookup;
         }
 
         internal unsafe void GetFunctionPointerAndInstantiationArgumentForOriginalLdFtnResult(IntPtr originalLdFtnResult, out IntPtr canonOriginalLdFtnResult, out IntPtr instantiationArgument)

src/coreclr/nativeaot/System.Private.Reflection.Execution/src/System.Private.Reflection.Execution.csproj

@@ -65,6 +65,9 @@
     <Compile Include="$(AotCommonPath)\System\Collections\Generic\LowLevelDictionary.cs">
       <Link>System\Collections\Generic\LowLevelDictionary.cs</Link>
     </Compile>
+    <Compile Include="$(CompilerCommonPath)\System\Collections\Generic\ArrayBuilder.cs">
+      <Link>System\Collections\Generic\ArrayBuilder.cs</Link>
+    </Compile>
     <Compile Include="$(CompilerCommonPath)\Internal\LowLevelLinq\LowLevelEnumerable.cs">
       <Link>Internal\LowLevelLinq\LowLevelEnumerable.cs</Link>
     </Compile>