Rollup merge of #47467 - arielb1:cleanup-shims, r=eddyb

remove noop landing pads in cleanup shims

No-op landing pads are already removed in the normal optimization pipeline - so also removing them on the shim pipeline should slightly improve codegen performance, as these cleanup blocks are known to hurt LLVM.

This un-regresses and is therefore a fix for #47442. However, the reporter of that issue should try using `-C panic=abort` instead of carefully avoiding panics.

r? @eddyb

src/test/codegen/issue-47442.rs

@@ -0,0 +1,32 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// check that we don't emit unneeded `resume` cleanup blocks for every
+// destructor.
+
+// CHECK-NOT: Unwind
+
+#![feature(test)]
+#![crate_type="rlib"]
+
+extern crate test;
+
+struct Foo {}
+
+impl Drop for Foo {
+    fn drop(&mut self) {
+        test::black_box(());
+    }
+}
+
+#[no_mangle]
+pub fn foo() {
+    let _foo = Foo {};
+}