Propagate tfGcSafe flag to generic instantiations (#10620)

Fixes a nasty endless loop in the generic instantiation phase.

compiler/semtypinst.nim

@@ -300,7 +300,6 @@ proc instCopyType*(cl: var TReplTypeVars, t: PType): PType =
 proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
   # tyGenericInvocation[A, tyGenericInvocation[A, B]]
   # is difficult to handle:
-  const eqFlags = eqTypeFlags + {tfGcSafe}
   var body = t.sons[0]
   if body.kind != tyGenericBody:
     internalError(cl.c.config, cl.info, "no generic body")
@@ -311,7 +310,7 @@ proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
   else:
     result = searchInstTypes(t)
 
-  if result != nil and eqFlags*result.flags == eqFlags*t.flags:
+  if result != nil and sameFlags(result, t):
     when defined(reportCacheHits):
       echo "Generic instantiation cached ", typeToString(result), " for ", typeToString(t)
     return
@@ -329,7 +328,7 @@ proc handleGenericInvocation(cl: var TReplTypeVars, t: PType): PType =
   if header != t:
     # search again after first pass:
     result = searchInstTypes(header)
-    if result != nil and eqFlags*result.flags == eqFlags*t.flags:
+    if result != nil and sameFlags(result, t):
       when defined(reportCacheHits):
         echo "Generic instantiation cached ", typeToString(result), " for ",
           typeToString(t), " header ", typeToString(header)

tests/generics/tgenerics_various.nim

@@ -242,3 +242,14 @@ block tvarargs_vs_generics:
   withDirectType "string"
   withOpenArray "string"
   withVarargs "string"
+
+block:
+  type
+    Que[T] {.gcsafe.} = object
+      x: T
+
+  proc `=`[T](q: var Que[T]; x: Que[T]) =
+    discard
+
+  var x: Que[int]
+  doAssert(x.x == 0)