420544a34a
rustc assumes that regular `extern "Rust"` functions unwind only if the `unwind` panic runtime is linked. `throw` was annotated as such, but unwound unconditionally. This could cause UB when a crate built with `-C panic=abort` called `throw` from `core` built with `-C panic=unwind`, since no terminator was added to handle the panic arising from calling an allegedly non-unwinding `extern "Rust"` function. rustc was taught to recognize this condition since https://github.com/rust-lang/rust/pull/144225 and prevented such linkage, but this caused regressions in https://github.com/rust-lang/rust/issues/148246, since this meant that Emscripten projects could not be built with `-C panic=abort` without recompiling std. The most straightforward solution would be to move `throw` into the `panic_unwind` crate, so that it's only compiled if the panic runtime is guaranteed to be `unwind`, but this is messy due to our architecture. Instead, move it into `unwind::wasm`, which is only compiled for bare-metal targets that default to `panic = "abort"`, rendering the issue moot.
The files here use the LLVM FileCheck framework, documented at https://llvm.org/docs/CommandGuide/FileCheck.html.
One extension worth noting is the use of revisions as custom prefixes for FileCheck. If your codegen test has different behavior based on the chosen target or different compiler flags that you want to exercise, you can use a revisions annotation, like so:
// revisions: aaa bbb
// [bbb] compile-flags: --flags-for-bbb
After specifying those variations, you can write different expected, or
explicitly unexpected output by using <prefix>-SAME: and <prefix>-NOT:,
like so:
// CHECK: expected code
// aaa-SAME: emitted-only-for-aaa
// aaa-NOT: emitted-only-for-bbb
// bbb-NOT: emitted-only-for-aaa
// bbb-SAME: emitted-only-for-bbb