[silgen] When emitting a top level error, end_lifetime the error after we have logged it.

This is not strictly necessary since we are going to be exiting the program, but
the ownership verifier thinks that the error is leaked otherwise. By using the
end_lifetime we avoid having a small increase in code-size since it is a no-op
after ownership is removed.

rdar://29791263

Author: gottesmm

lib/SILGen/SILGen.cpp

@@ -1535,6 +1535,14 @@ class SourceFileScope {
                             sgm.getASTContext().getIdentifier("errorInMain"),
                             sgm.Types.getEmptyTupleType(), {}, {error});
 
+        // Then end the lifetime of the error.
+        //
+        // We do this to appease the ownership verifier. We do not care about
+        // actually destroying the value since we are going to immediately exit,
+        // so this saves us a slight bit of code-size since end_lifetime is
+        // stripped out after ownership is removed.
+        SGF.B.createEndLifetime(moduleLoc, error);
+
         // Signal an abnormal exit by returning 1.
         SGF.Cleanups.emitCleanupsForReturn(CleanupLocation::get(moduleLoc),
                                            IsForUnwind);

test/SILGen/toplevel_errors.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-emit-silgen %s | %FileCheck %s
+// RUN: %target-swift-emit-silgen -enable-sil-ownership %s | %FileCheck %s
 
 enum MyError : Error {
   case A, B
@@ -21,6 +21,7 @@ throw MyError.A
 
 // CHECK: bb2([[T0:%.*]] : @owned $Error):
 // CHECK: builtin "errorInMain"([[T0]] : $Error)
+// CHECK: end_lifetime [[T0]]
 // CHECK: [[T0:%.*]] = integer_literal $Builtin.Int32, 1
 // CHECK: [[T1:%.*]] = struct $Int32 ([[T0]] : $Builtin.Int32)
 // CHECK: br bb1([[T1]] : $Int32)