[AddressLowering] Take from cast destination.

When lowering an unconditional_checked_cast from an address-only value
to a loadable value, the value with which to replace the original is a
load of the destination address of the unconditional_checked_cast_addr
to which the instruction was lowered.  In the case of non-trivial
values, that load must be a take.

Author: nate-chandler

lib/SILOptimizer/Mandatory/AddressLowering.cpp

@@ -3298,7 +3298,7 @@ void UseRewriter::visitUnconditionalCheckedCastInst(
       uncondCheckedCast->getLoc(), destAddr,
       destAddr->getType().isTrivial(*uncondCheckedCast->getFunction())
           ? LoadOwnershipQualifier::Trivial
-          : LoadOwnershipQualifier::Copy);
+          : LoadOwnershipQualifier::Take);
   nextBuilder.createDeallocStack(uncondCheckedCast->getLoc(), destAddr);
   uncondCheckedCast->replaceAllUsesWith(dest);
 }

test/SILOptimizer/address_lowering.sil

@@ -2077,6 +2077,20 @@ entry(%instance : @owned $T):
   return %retval : $()
 }
 
+// CHECK-LABEL: sil [ossa] @test_unconditional_checked_cast6 : {{.*}} {
+// CHECK:       {{bb[0-9]+}}([[INSTANCE:%[^,]+]] :
+// CHECK:         [[ADDR:%[^,]+]] = alloc_stack $Klass
+// CHECK:         unconditional_checked_cast_addr T in [[INSTANCE]]
+// CHECK:         [[KLASS:%[^,]+]] = load [take] [[ADDR]]
+// CHECK:         dealloc_stack [[ADDR]]
+// CHECK-LABEL: } // end sil function 'test_unconditional_checked_cast6'
+sil [ossa] @test_unconditional_checked_cast6 : $@convention(method) <T> (@in T) -> () {
+bb0(%instance : @owned $T):
+  %klass = unconditional_checked_cast %instance : $T to Klass
+  destroy_value %klass : $Klass
+  %retval = tuple ()
+  return %retval : $()
+}
 // CHECK-LABEL: sil [ossa] @test_yield_1_two_values : {{.*}} {
 // CHECK:         tuple_element_addr
 // CHECK:         tuple_element_addr