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Fix missing calls to drop on unwind with lto=fat; issue 64655.

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This commit is contained in:
Felix S. Klock II 2019-10-02 21:43:24 +02:00
parent 1e869133b9
commit 9fbb2a9b34
1 changed files with 38 additions and 13 deletions
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51
src/librustc_codegen_llvm/attributes.rs
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@ -273,25 +273,50 @@ pub fn from_fn_attrs(
} else if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::RUSTC_ALLOCATOR_NOUNWIND) {
// Special attribute for allocator functions, which can't unwind
false
} else if let Some(id) = id {
} else if let Some(_) = id {
// rust-lang/rust#64655, rust-lang/rust#63909: to minimize
// risk associated with changing cases where nounwind
// attribute is attached, this code is deliberately mimicking
// old control flow based on whether `id` is `Some` or `None`.
//
// However, in the long term we should either:
// - fold this into final else (i.e. stop inspecting `id`)
// - or better still: whole-heartedly adopt Rust PR #63909.
//
// see also Rust RFC 2753.
let sig = cx.tcx.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), &sig);
if cx.tcx.is_foreign_item(id) {
// Foreign items like `extern "C" { fn foo(); }` are assumed not to
// unwind
false
} else if sig.abi != Abi::Rust && sig.abi != Abi::RustCall {
// Any items defined in Rust that *don't* have the `extern` ABI are
// defined to not unwind. We insert shims to abort if an unwind
// happens to enforce this.
false
} else {
// Anything else defined in Rust is assumed that it can possibly
// unwind
if sig.abi == Abi::Rust || sig.abi == Abi::RustCall {
// Any Rust method (or `extern "Rust" fn` or `extern
// "rust-call" fn`) is explicitly allowed to unwind
// (unless it has no-unwind attribute, handled above).
true
} else {
// Anything else is either:
//
// 1. A foreign item (like `extern "C" { fn foo(); }`), or
//
// 2. A Rust item using a non-Rust ABI (like `extern "C" fn foo() { ... }`).
//
// Foreign items (case 1) are assumed to not unwind; it is
// UB otherwise. (At least for now; see also
// rust-lang/rust#63909 and Rust RFC 2753.)
//
// Items defined in Rust with non-Rust ABIs (case 2) are
// defined to not unwind. We insert shims to abort if an
// unwind happens to enforce this.
//
// In either case, we mark item as explicitly nounwind.
false
}
} else {
// assume this can possibly unwind, avoiding the application of a
// `nounwind` attribute below.
//
// (But: See comments in previous branch. Specifically, it is
// unclear whether there is real value in the assumption this
// can unwind. The conservatism here may just be papering over
// a real problem by making some UB a bit harder to hit.)
true
});