rustc: Implement custom panic runtimes

This commit is an implementation of [RFC 1513] which allows applications to
alter the behavior of panics at compile time. A new compiler flag, `-C panic`,
is added and accepts the values `unwind` or `panic`, with the default being
`unwind`. This model affects how code is generated for the local crate, skipping
generation of landing pads with `-C panic=abort`.

[RFC 1513]: https://github.com/rust-lang/rfcs/blob/master/text/1513-less-unwinding.md

Panic implementations are then provided by crates tagged with
`#![panic_runtime]` and lazily required by crates with
`#![needs_panic_runtime]`. The panic strategy (`-C panic` value) of the panic
runtime must match the final product, and if the panic strategy is not `abort`
then the entire DAG must have the same panic strategy.

With the `-C panic=abort` strategy, users can expect a stable method to disable
generation of landing pads, improving optimization in niche scenarios,
decreasing compile time, and decreasing output binary size. With the `-C
panic=unwind` strategy users can expect the existing ability to isolate failure
in Rust code from the outside world.

Organizationally, this commit dismantles the `sys_common::unwind` module in
favor of some bits moving part of it to `libpanic_unwind` and the rest into the
`panicking` module in libstd. The custom panic runtime support is pretty similar
to the custom allocator support with the only major difference being how the
panic runtime is injected (takes the `-C panic` flag into account).

1 files changed, 31 insertions, 0 deletions

diff --git a/src/test/codegen/lto-removes-invokes.rs b/src/test/codegen/lto-removes-invokes.rs
new file mode 100644
index 00000000000..b2f43489523
--- /dev/null
+++ b/src/test/codegen/lto-removes-invokes.rs
@@ -0,0 +1,31 @@
+// 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.
+
+// compile-flags: -C lto -C panic=abort -O
+// no-prefer-dynamic
+
+fn main() {
+    foo();
+}
+
+#[no_mangle]
+#[inline(never)]
+fn foo() {
+    let _a = Box::new(3);
+    bar();
+// CHECK-LABEL: foo
+// CHECK: call {{.*}} void @bar
+}
+
+#[inline(never)]
+#[no_mangle]
+fn bar() {
+    println!("hello!");
+}