implements display based subtype checking (6.4x faster without threads; 2.8x faster with threads) (#20781)

* WIP: fast 'of' operator based on the literature
* implement  display based subtype checking

Co-authored-by: Araq <rumpf_a@web.de>

lib/system.nim

@@ -1592,7 +1592,9 @@ when not defined(js) and defined(nimV2):
     TNimTypeV2 {.compilerproc.} = object
       destructor: pointer
       size: int
-      align: int
+      align: int16
+      depth: int16
+      display: ptr UncheckedArray[uint32] # classToken
       name: cstring
       traceImpl: pointer
       typeInfoV1: pointer # for backwards compat, usually nil

lib/system/arc.nim

@@ -227,8 +227,6 @@ template tearDownForeignThreadGc* =
   ## With `--gc:arc` a nop.
   discard
 
-type ObjCheckCache = array[0..1, PNimTypeV2]
-
 proc memcmp(str1, str2: cstring, n: csize_t): cint {.importc, header: "<string.h>".}
 
 func endsWith(s, suffix: cstring): bool {.inline.} =
@@ -242,19 +240,8 @@ func endsWith(s, suffix: cstring): bool {.inline.} =
 proc isObj(obj: PNimTypeV2, subclass: cstring): bool {.compilerRtl, inl.} =
   result = endsWith(obj.name, subclass)
 
-proc isObjSlowPath(obj: PNimTypeV2, subclass: cstring, cache: var ObjCheckCache): bool {.compilerRtl, inline.} =
-  if endsWith(obj.name, subclass):
-    cache[1] = obj
-    result = true
-  else:
-    cache[0] = obj
-    result = false
-
-proc isObjWithCache(obj: PNimTypeV2, subclass: cstring, cache: var ObjCheckCache): bool {.compilerRtl.} =
-  if cache[0] == obj: result = false
-  elif cache[1] == obj: result = true
-  else:
-    result = isObjSlowPath(obj, subclass, cache)
+proc isObjDisplayCheck(source: PNimTypeV2, targetDepth: int16, token: uint32): bool {.compilerRtl, inline.} =
+  result = targetDepth <= source.depth and source.display[targetDepth] == token
 
 proc chckObj(obj: PNimTypeV2, subclass: cstring) {.compilerRtl.} =
   # checks if obj is of type subclass: