[move-only] Disable move-only devirtualization.

It is not needed for correctness and hides most of the deinit related
optimizer bugs.

Author: atrick

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -156,8 +156,6 @@ static void addMandatoryDiagnosticOptPipeline(SILPassPipelinePlan &P) {
 
   // Check noImplicitCopy and move only types for objects and addresses.
   P.addMoveOnlyChecker();
-  // Convert last destroy_value to deinits.
-  P.addMoveOnlyDeinitDevirtualization();
   // Lower move only wrapped trivial types.
   P.addTrivialMoveOnlyTypeEliminator();
   // Check no uses after consume operator of a value in an address.

lib/SILOptimizer/Transforms/MoveOnlyDeinitDevirtualization.cpp

@@ -15,6 +15,13 @@
 /// This pass runs after move only checking has occurred and transforms last
 /// destroy_value of move only types into a call to the move only types deinit.
 ///
+/// TODO: This pass is disabled because it hides bugs in the common case in
+/// which optimization passes incorrectly remove the deinit, for example, by
+/// destructuring the aggregate rather than destroying it as a whole. Consider
+/// reeabling this pass later in the pipeline, after all other OSSA function
+/// passes have run. Also consider removing bailouts from this pass. If it's
+/// possible to devirtualize, then it should do it.
+///
 //===----------------------------------------------------------------------===//
 
 #define DEBUG_TYPE "sil-move-only-checker"

test/SILOptimizer/moveonly_lifetime.swift

@@ -38,9 +38,7 @@ func something()
 // CHECK:         apply [[BORROW_C]]([[INSTANCE]])
 //
 // TODO: Once we maximize lifetimes this should be below something.
-// CHECK:         [[DESTROY_C:%[^,]+]] = function_ref @$s17moveonly_lifetime1CVfD
-// CHECK:         [[INSTANCE:%.*]] = load [take] [[STACK]]
-// CHECK:         apply [[DESTROY_C]]([[INSTANCE]])
+// CHECK:         destroy_addr [[STACK]]
 //
 // CHECK:         [[SOMETHING:%[^,]+]] = function_ref @something
 // CHECK:         apply [[SOMETHING]]