SIL: change SILModule's scheduledForDeletion from a double linked list to a std::vector

include/swift/SIL/SILModule.h

@@ -217,7 +217,7 @@ private:
   /// This avoids dangling instruction pointers within the run of a pass and in
   /// analysis caches. Note that the analysis invalidation mechanism ensures
   /// that analysis caches are invalidated before flushDeletedInsts().
-  llvm::iplist<SILInstruction> scheduledForDeletion;
+  std::vector<SILInstruction*> scheduledForDeletion;
 
   /// The swift Module associated with this SILModule.
   ModuleDecl *TheSwiftModule;

lib/SIL/IR/SILModule.cpp

@@ -164,8 +164,8 @@ void SILModule::checkForLeaks() const {
   if (!getOptions().checkSILModuleLeaks)
     return;
 
-  int instsInModule = std::distance(scheduledForDeletion.begin(),
-                                    scheduledForDeletion.end());
+  int instsInModule = scheduledForDeletion.size();
+
   for (const SILFunction &F : *this) {
     const SILFunction *sn = &F;
     do {
@@ -280,11 +280,11 @@ void SILModule::scheduleForDeletion(SILInstruction *I) {
 }
 
 void SILModule::flushDeletedInsts() {
-  while (!scheduledForDeletion.empty()) {
-    SILInstruction *inst = &*scheduledForDeletion.begin();
-    scheduledForDeletion.erase(inst);
-    AlignedFree(inst);
+  for (SILInstruction *instToDelete : scheduledForDeletion) {
+    SILInstruction::destroy(instToDelete);
+    AlignedFree(instToDelete);
   }
+  scheduledForDeletion.clear();
 }
 
 SILWitnessTable *