Fix an edge case in GenericCloner which was not generating end_borrows for store_borrow

Generic Cloner creates store_borrow for in_guaranteed args in OSSA. We use PrunedLiveness
to compute the boundary of store_borrow for inserting end_borrows. However, if there is an escape
boundary cannot be found, and we insert end_borrows at function exits. FunctionExists are populated while cloning.
There is an edgecase, where the Generic Cloner is explicitly creating return instructions, these were not inserted
in FunctionExits, thereby missing an end_borrow on that path. This PR fixes it.

rdar://99874076

Author: meg-gupta

lib/SILOptimizer/Utils/GenericCloner.cpp

@@ -189,7 +189,8 @@ void GenericCloner::visitTerminator(SILBasicBlock *BB) {
       getBuilder().createDeallocStack(ASI->getLoc(), ASI);
     }
     if (ReturnValue) {
-      getBuilder().createReturn(RI->getLoc(), ReturnValue);
+      auto *NewReturn = getBuilder().createReturn(RI->getLoc(), ReturnValue);
+      FunctionExits.push_back(NewReturn);
       return;
     }
   } else if (OrigTermInst->isFunctionExiting()) {

test/SILOptimizer/specialize_ossa.sil

@@ -115,6 +115,18 @@ bb0(%0 : $*T, %1 : $*XXX<T>):
   return %9 : $Int32                              // id: %11
 }
 
+
+sil [ossa] [noinline] @XXX_foo_guaranteed_generic_return : $@convention(method) <T> (@in_guaranteed T, @in XXX<T>) -> @out T {
+bb0(%0 : $*T, %1 : $*T, %2 : $*XXX<T>):
+  %3 = address_to_pointer %1 : $*T to $Builtin.RawPointer
+  %4 = alloc_stack $T
+  %5 = struct_element_addr %2 : $*XXX<T>, #XXX.m_t
+  copy_addr [take] %5 to [initialization] %0 : $*T
+  dealloc_stack %4 : $*T
+  %t = tuple ()
+  return %t : $()
+}
+
 // Swift.Int32._convertFromBuiltinIntegerLiteral (Swift.Int32.Type)(Builtin.IntLiteral) -> Swift.Int32
 sil public_external [ossa] [transparent] @$sSi33_convertFromBuiltinIntegerLiteralySiBI_cSimF : $@convention(thin) (Builtin.IntLiteral, @thin Int32.Type) -> Int32 {
 bb0(%0 : $Builtin.IntLiteral, %1 : $@thin Int32.Type):
@@ -231,10 +243,21 @@ bb0(%arg : @guaranteed $Builtin.NativeObject):
   apply %9(%15g) : $@convention(thin) (Int32) -> ()
   destroy_addr %11g : $*Builtin.NativeObject
   dealloc_stack %11g : $*Builtin.NativeObject    // id: %17
-  destroy_addr %0 : $*XXX<Builtin.NativeObject>
-  dealloc_stack %0 : $*XXX<Builtin.NativeObject> // id: %19
-  %18 = tuple ()                                  // user: %20
-  return %18 : $()                                // id: %20
+
+  %17 = function_ref @XXX_foo_guaranteed_generic_return : $@convention(method) <T> (@in_guaranteed T, @in XXX<T>) -> @out T
+  %18 = alloc_stack $Builtin.NativeObject
+  %19 = alloc_stack $Builtin.NativeObject
+  %arg3 = copy_value %arg : $Builtin.NativeObject
+  store %arg3 to [init] %18 : $*Builtin.NativeObject
+  apply %17<Builtin.NativeObject>(%19, %18, %0) : $@convention(method) <T> (@in_guaranteed T, @in XXX<T>) -> @out T
+  destroy_addr %18 : $*Builtin.NativeObject
+  destroy_addr %19 : $*Builtin.NativeObject
+  dealloc_stack %19 : $*Builtin.NativeObject
+  dealloc_stack %18 : $*Builtin.NativeObject
+
+  dealloc_stack %0 : $*XXX<Builtin.NativeObject>
+  %t = tuple ()
+  return %t : $()
 }
 
 // specialize.useClosure <A>(fun : () -> A) -> A