SILOptimizer: Remove witness table marking from DeadFunctionElimination

This logic was unconditionally disabled and incorrect.

Author: slavapestov

lib/SILOptimizer/IPO/DeadFunctionElimination.cpp

@@ -201,27 +201,13 @@ class DeadFunctionAndGlobalElimination {
           }
         } break;
 
-        case SILWitnessTable::AssociatedConformance: {
-          ProtocolConformanceRef CRef =
-             entry.getAssociatedConformanceWitness().Witness;
-          if (CRef.isConcrete())
-            ensureAliveConformance(CRef.getConcrete());
-          break;
-        }
+        case SILWitnessTable::AssociatedConformance:
         case SILWitnessTable::BaseProtocol:
-          ensureAliveConformance(entry.getBaseProtocolWitness().Witness);
-          break;
-
         case SILWitnessTable::Invalid:
         case SILWitnessTable::AssociatedType:
           break;
       }
     }
-
-    for (const auto &conf : WT->getConditionalConformances()) {
-      if (conf.isConcrete())
-        ensureAliveConformance(conf.getConcrete());
-    }
   }
 
   /// Marks the \p global and all functions, which are referenced from its
@@ -279,14 +265,6 @@ class DeadFunctionAndGlobalElimination {
       makeAlive(global);
   }
 
-  /// Marks a witness table as alive if it is not alive yet.
-  void ensureAliveConformance(const ProtocolConformance *C) {
-    SILWitnessTable *WT = Module->lookUpWitnessTable(C);
-    if (!WT || isAlive(WT))
-      return;
-    makeAlive(WT);
-  }
-
   /// Returns true if the implementation of method \p FD in class \p ImplCl
   /// may be called when the type of the class_method's operand is \p MethodCl.
   /// Both, \p MethodCl and \p ImplCl, may by null if not known or if it's a
@@ -322,7 +300,7 @@ class DeadFunctionAndGlobalElimination {
       if (!isAlive(FImpl.F) &&
           canHaveSameImplementation(FD, MethodCl,
                                     FImpl.Impl.get<ClassDecl *>())) {
-        makeAlive(FImpl.F);
+        ensureAlive(FImpl.F);
       } else {
         allImplsAreCalled = false;
       }
@@ -341,9 +319,9 @@ class DeadFunctionAndGlobalElimination {
       if (auto Conf = FImpl.Impl.dyn_cast<ProtocolConformance *>()) {
         SILWitnessTable *WT = Module->lookUpWitnessTable(Conf);
         if (!WT || isAlive(WT))
-          makeAlive(FImpl.F);
+          ensureAlive(FImpl.F);
       } else {
-        makeAlive(FImpl.F);
+        ensureAlive(FImpl.F);
       }
     }
   }