Workaround LLVM optimizer bug by not marking &mut pointers as noalias

src/librustc_trans/trans/attributes.rs

@@ -265,7 +265,7 @@ pub fn from_fn_type<'a, 'tcx>(ccx: &CrateContext<'a, 'tcx>, fn_type: ty::Ty<'tcx
                 // on memory dependencies rather than pointer equality
                 let interior_unsafe = mt.ty.type_contents(ccx.tcx()).interior_unsafe();
 
-                if mt.mutbl == hir::MutMutable || !interior_unsafe {
+                if mt.mutbl != hir::MutMutable && !interior_unsafe {
                     attrs.arg(idx, llvm::Attribute::NoAlias);
                 }
 

src/test/auxiliary/issue-29485.rs

@@ -0,0 +1,26 @@
+// Copyright 2016 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.
+
+#![crate_name="a"]
+#![crate_type = "lib"]
+
+pub struct X(pub u8);
+
+impl Drop for X {
+    fn drop(&mut self) {
+        assert_eq!(self.0, 1)
+    }
+}
+
+pub fn f(x: &mut X, g: fn()) {
+    x.0 = 1;
+    g();
+    x.0 = 0;
+}

src/test/codegen/function-arguments.rs

@@ -51,14 +51,16 @@ pub fn named_borrow<'r>(_: &'r i32) {
 pub fn unsafe_borrow(_: &UnsafeInner) {
 }
 
-// CHECK: @mutable_unsafe_borrow(%UnsafeInner* noalias dereferenceable(2))
+// CHECK: @mutable_unsafe_borrow(%UnsafeInner* dereferenceable(2))
 // ... unless this is a mutable borrow, those never alias
+// ... except that there's this LLVM bug that forces us to not use noalias, see #29485
 #[no_mangle]
 pub fn mutable_unsafe_borrow(_: &mut UnsafeInner) {
 }
 
-// CHECK: @mutable_borrow(i32* noalias dereferenceable(4))
+// CHECK: @mutable_borrow(i32* dereferenceable(4))
 // FIXME #25759 This should also have `nocapture`
+// ... there's this LLVM bug that forces us to not use noalias, see #29485
 #[no_mangle]
 pub fn mutable_borrow(_: &mut i32) {
 }
@@ -100,8 +102,9 @@ fn helper(_: usize) {
 fn slice(_: &[u8]) {
 }
 
-// CHECK: @mutable_slice(i8* noalias nonnull, [[USIZE]])
+// CHECK: @mutable_slice(i8* nonnull, [[USIZE]])
 // FIXME #25759 This should also have `nocapture`
+// ... there's this LLVM bug that forces us to not use noalias, see #29485
 #[no_mangle]
 fn mutable_slice(_: &mut [u8]) {
 }

src/test/run-pass/issue-29485.rs

@@ -0,0 +1,25 @@
+// Copyright 2016 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.
+
+// aux-build:issue-29485.rs
+
+#[feature(recover)]
+
+extern crate a;
+
+fn main() {
+    let _ = std::thread::spawn(move || {
+        a::f(&mut a::X(0), g);
+    }).join();
+}
+
+fn g() {
+    panic!();
+}