Send delete notifications when basic block arguments are being erased.

Author: swiftix

include/swift/SIL/SILBasicBlock.h

@@ -167,7 +167,7 @@ public llvm::ilist_node<SILBasicBlock>, public SILAllocated<SILBasicBlock> {
   SILArgument *replaceBBArg(unsigned i, SILType Ty, const ValueDecl *D=nullptr);
 
   /// Erase a specific argument from the arg list.
-  void eraseBBArg(int Index) { BBArgList.erase(BBArgList.begin() + Index); }
+  void eraseBBArg(int Index);
 
   /// Allocate a new argument of type \p Ty and append it to the argument
   /// list. Optionally you can pass in a value decl parameter.

lib/SIL/SILBasicBlock.cpp

@@ -118,6 +118,12 @@ SILArgument *SILBasicBlock::insertBBArg(bbarg_iterator Iter, SILType Ty,
   return new (getModule()) SILArgument(this, Iter, Ty, D);
 }
 
+void SILBasicBlock::eraseBBArg(int Index) {
+  // Notify the delete handlers that this BB argument is going away.
+  getModule().notifyDeleteHandlers(getBBArg(Index));
+  BBArgList.erase(BBArgList.begin() + Index);
+}
+
 /// \brief Splits a basic block into two at the specified instruction.
 ///
 /// Note that all the instructions BEFORE the specified iterator