JIT: Mark certain intrinsics as non-escaping

src/coreclr/jit/objectalloc.cpp

@@ -1139,6 +1139,25 @@ bool ObjectAllocator::CanLclVarEscapeViaParentStack(ArrayStack<GenTree*>* parent
                     canLclVarEscapeViaParentStack =
                         !Compiler::s_helperCallProperties.IsNoEscape(comp->eeGetHelperNum(asCall->gtCallMethHnd));
                 }
+                else if (asCall->IsSpecialIntrinsic())
+                {
+                    // Some known special intrinsics don't escape. At this moment, only the ones accepting byrefs
+                    // are supported. In order to support more intrinsics accepting objects, we need extra work
+                    // on the VM side which is not ready for that yet.
+                    //
+                    switch (comp->lookupNamedIntrinsic(asCall->gtCallMethHnd))
+                    {
+                        case NI_System_SpanHelpers_ClearWithoutReferences:
+                        case NI_System_SpanHelpers_Fill:
+                        case NI_System_SpanHelpers_Memmove:
+                        case NI_System_SpanHelpers_SequenceEqual:
+                            canLclVarEscapeViaParentStack = false;
+                            break;
+
+                        default:
+                            break;
+                    }
+                }
 
                 // Note there is nothing special here about the parent being a call. We could move all this processing
                 // up to the caller and handle any sort of tree that could lead to escapes this way.

src/coreclr/jit/utils.cpp

@@ -1669,6 +1669,13 @@ void HelperCallProperties::init()
                 isPure     = true;
                 break;
 
+            case CORINFO_HELP_MEMCPY:
+            case CORINFO_HELP_MEMZERO:
+            case CORINFO_HELP_MEMSET:
+            case CORINFO_HELP_NATIVE_MEMSET:
+                isNoEscape = true;
+                break;
+
             case CORINFO_HELP_LDELEMA_REF:
                 isPure = true;
                 break;