special `link_name` confuses LLVM

[usamoi]

Inspired by #155495, I tried this code:

unsafe extern "C" {
    #[link_name = "\0"]
    safe fn hack();
}

pub fn main() {
    hack();
}

I expected to see this happen: rustc works or emits errors

Instead, this happened:

rustc: /checkout/src/llvm-project/llvm/lib/IR/Value.cpp:346: void llvm::Value::setNameImpl(const Twine &): Assertion `!NameRef.contains(0) && "Null bytes are not allowed in names"' failed.

Also, I tried this code:

unsafe extern "C" {
    #[link_name = ""]
    safe fn hack();
}

pub fn main() {
    hack();
}

I expected to see this happen:

rust-lld: error: undefined symbol: 

or rustc emits errors.

Instead, this happened:

rust-lld: error: undefined symbol: anon.ba0403d3885badc6dc2b3e34422528cb.0

Meta

There must be llvm.assertions = true in bootstrap.toml.

[bjorn3]

The first issue is roughly a duplicate of #155484. I recall seeing a report for the other issue somewhere, but I don't remember where. Might have been zulip.

[folkertdev]

kind of related to #155065 and #155515 too, most similar attributes do check for \0, likely this was just missed.