Fix a minor issue in ExistentialSpecializer for OSSA (swiftlang#36180)

While cloning arguments for existential specializer, do not create copy
for object types. Currently, for guaranteed parameter types it
unnecessarily creates a copy and cleans it up with a destroy. The
discrepency is seen when cloning an instruction like open_existential_ref
which was previously using guaranteed operand and had guaranteed
forwarding ownership, is now replaced to have the owned copy as its
operand during cloning.

Author: meg-gupta

lib/SILOptimizer/FunctionSignatureTransforms/ExistentialTransform.cpp

@@ -108,11 +108,8 @@ void ExistentialSpecializerCloner::cloneAndPopulateFunction() {
     // A return location can't be used for a non-return instruction.
     auto loc = RegularLocation::getAutoGeneratedLocation();
     for (SILValue cleanupVal : CleanupValues) {
-      if (cleanupVal.getOwnershipKind() == OwnershipKind::Guaranteed) {
-        Builder.emitEndBorrowOperation(loc, cleanupVal);
-      } else {
-        Builder.emitDestroyOperation(loc, cleanupVal);
-      }
+      assert(cleanupVal.getOwnershipKind() != OwnershipKind::Guaranteed);
+      Builder.emitDestroyOperation(loc, cleanupVal);
     }
 
     for (auto *ASI : llvm::reverse(AllocStackInsts))
@@ -240,10 +237,6 @@ void ExistentialSpecializerCloner::cloneArguments(
         }
         NewArgValue =
             NewFBuilder.emitLoadValueOperation(InsertLoc, NewArg, qual);
-      } else {
-        if (NewFBuilder.hasOwnership() && !origConsumed) {
-          NewArgValue = NewFBuilder.emitCopyValueOperation(InsertLoc, NewArg);
-        }
       }
 
       ///  Simple case: Create an init_existential.
@@ -262,15 +255,6 @@ void ExistentialSpecializerCloner::cloneArguments(
                                             StoreOwnershipQualifier::Init);
         InitRef = alloc;
         AllocStackInsts.push_back(alloc);
-      } else {
-        // Otherwise in ossa, we need to add init existential ref as something
-        // to be cleaned up. In non-ossa, we do not insert the copies, so we do
-        // not need to do it then.
-        //
-        // TODO: This would be simpler if we had managed value/cleanup scopes.
-        if (NewFBuilder.hasOwnership() && !origConsumed) {
-          CleanupValues.push_back(InitRef);
-        }
       }
 
       entryArgs.push_back(InitRef);

test/SILOptimizer/existential_transform_extras_ossa.sil

@@ -20,6 +20,26 @@ internal class Klass2 : P {
   init()
 }
 
+internal class Klass3 {
+}
+
+extension Klass3 : P {
+  @inline(never) func foo() -> Int32
+}
+
+internal class Klass4 : Klass3 {
+  func foo() -> Int {
+    return 10
+  }
+}
+
+sil private [transparent] [thunk] @Klass4foo : $@convention(witness_method: P) (@in_guaranteed Klass4) -> Int32 {
+bb0(%0 : $*Klass4):
+  %1 = integer_literal $Builtin.Int32, 10
+  %2 = struct $Int32 (%1 : $Builtin.Int32)
+  return %2 : $Int32
+}
+
 @inline(never) internal func wrap_foo_ncp(a: inout P, b: inout P) -> Int32
 
 @inline(never) func ncp()
@@ -264,3 +284,31 @@ bb0(%0 : @guaranteed $PlotView):
   %v = tuple ()
   return %v : $()
 }
+
+// CHECK-LABEL: sil shared [ossa] @$s35testExistentialSpecializeGuaranteedTf4e_n : 
+// CHECK:  [[VAL1:%.*]] = init_existential_ref %0
+// CHECK:  [[VAL2:%.*]] = open_existential_ref [[VAL1]]
+// CHECK-LABEL: } // end sil function '$s35testExistentialSpecializeGuaranteedTf4e_n'
+sil hidden [ossa] @testExistentialSpecializeGuaranteed : $@convention(thin) (@guaranteed Klass3 & P) -> Int32 {
+bb0(%0 : @guaranteed $Klass3 & P):
+  %2 = open_existential_ref %0 : $Klass3 & P to $@opened("77949BFA-77BC-11EB-BC0E-F2189810406F") Klass3 & P
+  %3 = alloc_stack $@opened("77949BFA-77BC-11EB-BC0E-F2189810406F") Klass3 & P
+  %4 = store_borrow %2 to %3 : $*@opened("77949BFA-77BC-11EB-BC0E-F2189810406F") Klass3 & P
+  %5 = witness_method $@opened("77949BFA-77BC-11EB-BC0E-F2189810406F") Klass3 & P, #P.foo : <Self where Self : P> (Self) -> () -> Int32, %2 : $@opened("77949BFA-77BC-11EB-BC0E-F2189810406F") Klass3 & P : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@in_guaranteed τ_0_0) -> Int32
+  %6 = apply %5<@opened("77949BFA-77BC-11EB-BC0E-F2189810406F") Klass3 & P>(%3) : $@convention(witness_method: P) <τ_0_0 where τ_0_0 : P> (@in_guaranteed τ_0_0) -> Int32
+  dealloc_stack %3 : $*@opened("77949BFA-77BC-11EB-BC0E-F2189810406F") Klass3 & P
+  return %6 : $Int32
+}
+
+sil hidden [ossa] @entrypoint : $@convention(thin) (@guaranteed Klass4) -> Int32 {
+bb0(%0 : @guaranteed $Klass4):
+  %1 = init_existential_ref %0 : $Klass4 : $Klass4, $Klass3 & P
+  %func = function_ref @testExistentialSpecializeGuaranteed : $@convention(thin) (@guaranteed Klass3 & P) -> Int32
+  %res = apply %func(%1) : $@convention(thin) (@guaranteed Klass3 & P) -> Int32
+  return %res : $Int32
+}
+
+sil_witness_table hidden Klass4: P module devirtualize_protocol_composition {
+  method #P.foo: <Self where Self : P> (Self) -> () -> Int32 : @Klass4foo
+}
+