CastOptimizer: fix a minor bug with memory lifetime.

This was not a real leak, because it only happened in an error condition where the block ends in an trap instructon anyway.
But it must be fixed to make the MemoryLifetimeVerifier happy.

Author: eeckstein

lib/SILOptimizer/Utils/CastOptimizer.cpp

@@ -1623,6 +1623,7 @@ SILInstruction *CastOptimizer::optimizeUnconditionalCheckedCastAddrInst(
       Builder.emitStoreValueOperation(Loc, undef, dynamicCast.getDest(),
                                       StoreOwnershipQualifier::Init);
     }
+    Builder.emitDestroyAddr(Loc, Inst->getSrc());
     auto *TrapI = Builder.createBuiltinTrap(Loc);
     eraseInstAction(Inst);
     Builder.setInsertionPoint(std::next(TrapI->getIterator()));

test/SILOptimizer/sil_combine_uncheck.sil

@@ -39,6 +39,7 @@ bb0(%0 : $Builtin.Int1):
 // CHECK-LABEL: sil @test_unconditional_checked_cast_addr_fail
 // CHECK: bb0
 // CHECK-NEXT: store undef
+// CHECK-NEXT: destroy_addr
 // CHECK-NEXT: builtin "int_trap"
 // CHECK: unreachable
 // CHECK: }