Rollup merge of rust-lang#52825 - RalfJung:codegen, r=alexcrichton

Make sure rust-lang#47772 does not regress

Mostly to make my life in rust-lang#52206 harder.^^

Or should I just add that test there?

src/test/codegen/slice-position-bounds-check.rs

@@ -0,0 +1,34 @@
+// 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.
+
+// no-system-llvm
+// compile-flags: -O
+#![crate_type = "lib"]
+
+fn search<T: Ord + Eq>(arr: &mut [T], a: &T) -> Result<usize, ()> {
+    match arr.iter().position(|x| x == a) {
+        Some(p) => {
+            Ok(p)
+        },
+        None => Err(()),
+    }
+}
+
+// CHECK-LABEL: @position_no_bounds_check
+#[no_mangle]
+pub fn position_no_bounds_check(y: &mut [u32], x: &u32, z: &u32) -> bool {
+    // This contains "call assume" so we cannot just rule out all calls
+    // CHECK-NOT: panic
+    if let Ok(p) = search(y, x) {
+      y[p] == *z
+    } else {
+      false
+    }
+}