JIT: switch escape analysis flagging to look for calls returning IEnumerator<T> (#116978)

Conditional Escape Analysis (CEA) is currently driven by flagging GDV calls
made to `IEnumerable<T>.GetEnumerator`. Generalize this slightly to instead look
for any call that returns an `IEnumerator<T>`, since there are some classes that
return enumerators via other calls. These calls likely won't be GDVs; I will address
adapting CEA to handle that in subsequent changes.

Author: AndyAyersMS

src/coreclr/jit/importer.cpp

@@ -6929,30 +6929,33 @@ void Compiler::impImportBlockCode(BasicBlock* block)
                     }
 
                     // If we see a local being assigned the result of a GDV-inlineable
-                    // IEnumerable<T>.GetEnumerator, keep track of both the local and the call.
+                    // GetEnumerator call, keep track of both the local and the call.
                     //
                     if (op1->OperIs(GT_RET_EXPR))
                     {
-                        JITDUMP(".... checking for GDV of IEnumerable<T>...\n");
+                        JITDUMP(".... checking for GDV returning IEnumerator<T>...\n");
 
-                        GenTreeCall* const call = op1->AsRetExpr()->gtInlineCandidate;
-                        NamedIntrinsic     ni   = NI_Illegal;
+                        bool                 isEnumeratorT = false;
+                        GenTreeCall* const   call          = op1->AsRetExpr()->gtInlineCandidate;
+                        bool                 isExact       = false;
+                        bool                 isNonNull     = false;
+                        CORINFO_CLASS_HANDLE retCls        = gtGetClassHandle(call, &isExact, &isNonNull);
 
-                        // TODO -- handle CT_INDIRECT virtuals here too
-                        // but we don't have the right method handle
-                        //
-                        if (call->gtCallType == CT_USER_FUNC)
-                        {
-                            ni = lookupNamedIntrinsic(call->gtCallMethHnd);
-                        }
-                        else if (call->IsGuardedDevirtualizationCandidate())
+                        if ((retCls != NO_CLASS_HANDLE) && info.compCompHnd->isIntrinsicType(retCls))
                         {
-                            JITDUMP("No GDV IEnumerable<T> check for [%06u]\n", dspTreeID(call));
+                            const char* namespaceName;
+                            const char* className = info.compCompHnd->getClassNameFromMetadata(retCls, &namespaceName);
+
+                            if ((strcmp(namespaceName, "System.Collections.Generic") == 0) &&
+                                (strcmp(className, "IEnumerator`1") == 0))
+                            {
+                                isEnumeratorT = true;
+                            }
                         }
 
-                        if (ni == NI_System_Collections_Generic_IEnumerable_GetEnumerator)
+                        if (isEnumeratorT)
                         {
-                            JITDUMP("V%02u value is GDV of IEnumerable<T>.GetEnumerator\n", lclNum);
+                            JITDUMP("V%02u value is IEnumerator<T> via GDV\n", lclNum);
                             lvaTable[lclNum].lvIsEnumerator = true;
                             JITDUMP("Flagging [%06u] for enumerator cloning via V%02u\n", dspTreeID(call), lclNum);
                             getImpEnumeratorGdvLocalMap()->Set(call, lclNum);

src/coreclr/jit/importercalls.cpp

@@ -10342,13 +10342,6 @@ NamedIntrinsic Compiler::lookupNamedIntrinsic(CORINFO_METHOD_HANDLE method)
                             result = NI_System_Collections_Generic_EqualityComparer_get_Default;
                         }
                     }
-                    else if (strcmp(className, "IEnumerable`1") == 0)
-                    {
-                        if (strcmp(methodName, "GetEnumerator") == 0)
-                        {
-                            result = NI_System_Collections_Generic_IEnumerable_GetEnumerator;
-                        }
-                    }
                 }
                 else if (strcmp(namespaceName, "Numerics") == 0)
                 {

src/coreclr/jit/namedintrinsiclist.h

@@ -259,7 +259,6 @@ enum NamedIntrinsic : unsigned short
     //
     NI_System_SZArrayHelper_GetEnumerator,
     NI_System_Array_T_GetEnumerator,
-    NI_System_Collections_Generic_IEnumerable_GetEnumerator,
 };
 
 #endif // _NAMEDINTRINSICLIST_H_

src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/CompilerServices/IntrinsicAttribute.cs

@@ -4,7 +4,7 @@
 namespace System.Runtime.CompilerServices
 {
     // This attribute is only for use in a Class Library
-    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Field, Inherited = false)]
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Field | AttributeTargets.Interface, Inherited = false)]
     internal sealed class IntrinsicAttribute : Attribute
     {
     }

src/libraries/System.Private.CoreLib/src/System/Collections/Generic/IEnumerator.cs

@@ -1,10 +1,13 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Runtime.CompilerServices;
+
 namespace System.Collections.Generic
 {
     // Base interface for all generic enumerators, providing a simple approach
     // to iterating over a collection.
+    [Intrinsic]
     public interface IEnumerator<out T> : IDisposable, IEnumerator
         where T : allows ref struct
     {

src/libraries/System.Private.CoreLib/src/System/Runtime/CompilerServices/IntrinsicAttribute.cs

@@ -6,7 +6,7 @@ namespace System.Runtime.CompilerServices
     // Calls to methods or references to fields marked with this attribute may be replaced at
     // some call sites with jit intrinsic expansions.
     // Types marked with this attribute may be specially treated by the runtime/compiler.
-    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Field, Inherited = false)]
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Field | AttributeTargets.Interface, Inherited = false)]
     internal sealed class IntrinsicAttribute : Attribute
     {
     }