SIL: Visit pack conformances in DeadFunctionElimination

Author: slavapestov

Diff for: lib/SILOptimizer/IPO/DeadFunctionElimination.cpp

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "sil-dead-function-elimination"
+#include "swift/AST/PackConformance.h"
 #include "swift/AST/ProtocolConformance.h"
 #include "swift/Basic/Assertions.h"
 #include "swift/SIL/InstructionUtils.h"
@@ -204,12 +205,11 @@ class DeadFunctionAndGlobalElimination {
         case SILWitnessTable::AssociatedConformance: {
           ProtocolConformanceRef CRef =
              entry.getAssociatedConformanceWitness().Witness;
-          if (CRef.isConcrete())
-            ensureAliveConformance(CRef.getConcrete());
+          ensureAliveConformance(CRef);
           break;
         }
         case SILWitnessTable::BaseProtocol:
-          ensureAliveConformance(entry.getBaseProtocolWitness().Witness);
+          ensureAliveConformance(ProtocolConformanceRef(entry.getBaseProtocolWitness().Witness));
           break;
 
         case SILWitnessTable::Invalid:
@@ -219,8 +219,7 @@ class DeadFunctionAndGlobalElimination {
     }
 
     for (const auto &conf : WT->getConditionalConformances()) {
-      if (conf.isConcrete())
-        ensureAliveConformance(conf.getConcrete());
+      ensureAliveConformance(conf);
     }
   }
 
@@ -280,11 +279,22 @@ class DeadFunctionAndGlobalElimination {
   }
 
   /// 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);
+  void ensureAliveConformance(ProtocolConformanceRef conformance) {
+    if (conformance.isConcrete()) {
+      auto *concrete = conformance.getConcrete();
+      SILWitnessTable *WT = Module->lookUpWitnessTable(concrete);
+      if (!WT || isAlive(WT))
+        return;
+      makeAlive(WT);
+
+      // FIXME: If 'concrete' is a SpecializedProtocolConformance,
+      // do we need to check its substitution map and root conformance
+      // recursively?
+    } else if (conformance.isPack()) {
+      auto *pack = conformance.getPack();
+      for (auto patternConf : pack->getPatternConformances())
+        ensureAliveConformance(patternConf);
+    }
   }
 
   /// Returns true if the implementation of method \p FD in class \p ImplCl