SILOptimizer: Remove witness table marking from DeadFunctionElimination

This logic was unconditionally disabled and incorrect.

Author: slavapestov

lib/SILOptimizer/IPO/DeadFunctionElimination.cpp

@@ -154,11 +154,6 @@ class DeadFunctionAndGlobalElimination {
     return AliveFunctionsAndTables.count(F) != 0;
   }
 
-  /// Returns true if a witness table is marked as alive.
-  bool isAlive(SILWitnessTable *WT) {
-    return AliveFunctionsAndTables.count(WT) != 0;
-  }
-
   /// Returns true if a global variable is marked as alive.
   bool isAlive(SILGlobalVariable *global) {
     return AliveFunctionsAndTables.count(global) != 0;
@@ -183,7 +178,6 @@ class DeadFunctionAndGlobalElimination {
     LLVM_DEBUG(llvm::dbgs() << "    scan witness table " << WT->getName()
                             << '\n');
 
-    AliveFunctionsAndTables.insert(WT);
     for (const SILWitnessTable::Entry &entry : WT->getEntries()) {
       switch (entry.getKind()) {
         case SILWitnessTable::Method: {
@@ -201,27 +195,13 @@ 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 +259,6 @@ 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
@@ -338,13 +310,7 @@ class DeadFunctionAndGlobalElimination {
       return;
     mi->methodIsCalled = true;
     for (FuncImpl &FImpl : mi->implementingFunctions) {
-      if (auto Conf = FImpl.Impl.dyn_cast<ProtocolConformance *>()) {
-        SILWitnessTable *WT = Module->lookUpWitnessTable(Conf);
-        if (!WT || isAlive(WT))
-          makeAlive(FImpl.F);
-      } else {
-        makeAlive(FImpl.F);
-      }
+      makeAlive(FImpl.F);
     }
   }
 
@@ -613,11 +579,6 @@ class DeadFunctionAndGlobalElimination {
         MethodInfo *mi = getMethodInfo(fd, /*isWitnessTable*/ true);
         ensureAliveProtocolMethod(mi);
       }
-
-      // We don't do dead witness table elimination right now. So we assume
-      // that all witness tables are alive. Dead witness table elimination is
-      // done in IRGen by lazily emitting witness tables.
-      makeAlive(&WT);
     }
 
     // Check default witness methods.
@@ -763,18 +724,6 @@ class DeadFunctionAndGlobalElimination {
       }
     }
 
-    // Next step: delete dead witness tables.
-    SILModule::WitnessTableListType &WTables = Module->getWitnessTableList();
-    for (auto Iter = WTables.begin(), End = WTables.end(); Iter != End;) {
-      SILWitnessTable *Wt = &*Iter;
-      Iter++;
-      if (!isAlive(Wt)) {
-        LLVM_DEBUG(llvm::dbgs() << "  erase dead witness table "
-                                << Wt->getName() << '\n');
-        Module->deleteWitnessTable(Wt);
-      }
-    }
-
     // Last step: delete all dead functions.
     for (SILFunction *deadFunc : DeadFunctions) {
       LLVM_DEBUG(llvm::dbgs() << "  erase dead function " << deadFunc->getName()