Auto merge of #40549 - alexcrichton:uwtable-everywhere, r=eddyb

rustc: Always emit the `uwtable` attribute on Windows

This commit alters the translation layer to unconditionally emit the `uwtable`
LLVM attribute on Windows regardless of the `no_landing_pads` setting.
Previously I believe we omitted this attribute as an optimization when the
`-Cpanic=abort` flag was passed, but this unfortunately caused problems for
Gecko.

It [was discovered] that there was trouble unwinding through Rust functions due
to foreign exceptions such as illegal instructions or otherwise in-practice
methods used to abort a process. In testing it looked like the major difference
between a working binary and a non-working binary is indeed this `uwtable`
attribute, but this PR has unfortunately not been thoroughly tested in terms of
compiling Gecko with `-C panic=abort` *and* this PR to see whether it works, so
this is still somewhat working on just suspicion.

[was discovered]: https://bugzilla.mozilla.org/show_bug.cgi?id=1302078

1 files changed, 41 insertions, 0 deletions

diff --git a/src/test/codegen/panic-abort-windows.rs b/src/test/codegen/panic-abort-windows.rs
new file mode 100644
index 00000000000..2ab15277084
--- /dev/null
+++ b/src/test/codegen/panic-abort-windows.rs
@@ -0,0 +1,41 @@
+// Copyright 2015 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.
+
+// ignore-tidy-linelength
+
+// This test is for *-windows-msvc only.
+// ignore-android
+// ignore-bitrig
+// ignore-macos
+// ignore-dragonfly
+// ignore-freebsd
+// ignore-haiku
+// ignore-ios
+// ignore-linux
+// ignore-netbsd
+// ignore-openbsd
+// ignore-solaris
+// ignore-emscripten
+
+// compile-flags: -C no-prepopulate-passes -C panic=abort -O
+
+#![crate_type = "lib"]
+
+// CHECK: Function Attrs: uwtable
+// CHECK-NEXT: define void @normal_uwtable()
+#[no_mangle]
+pub fn normal_uwtable() {
+}
+
+// CHECK: Function Attrs: nounwind uwtable
+// CHECK-NEXT: define void @extern_uwtable()
+#[no_mangle]
+pub extern fn extern_uwtable() {
+}