rustc opt parsing: -C "llvm-args=-mcpu=arm1176jzf-s" doesn't get whole input

[pnkfelix]

This was reported by a user on IRC.

https://gist.github.com/thebreadcat/b47c0f49d736a990b556

Shell

$ rustc --target=arm-unknown-linux-gnueabihf main.rs -C linker=arm-linux-gnueabihf-g++ -C "llvm-args=-mcpu=arm1176jzf-s"
rustc: Unknown command line argument '-mcpu=arm1176jzf-s'. Try: 'rustc -help'
rustc: Did you mean '-debug=arm1176jzf-s'?

I am logging it here in the hopes that I remember to look at it again later when I look into hacking a little on getopts (for #14223)

[alexcrichton]

This is not a bug in rustc opt parsing, but rather this message is being printed from LLVM. From what I can tell, rustc is correctly passing through the -mcpu=arm1176jzf-s to LLVM, and then LLVM isn't recognizing it.

Perhaps we could be clearer with an error?

[frewsxcv]

Can anyone confirm if this is still an issue? There have been at least a few LLVM upgrades since this was last updated

[bluss]

It seems to be an issue still.

Only certain kinds of arguments are accepted by llvm-args, different kinds of pass options are accepted. I don't think it's intentional..

[JinShil]

I believe this is the same issue as #26338. The arguments recognized by llc and the arguments recognized by llvm::cl::ParseCommandLineOptions() API are different. The Rust compiler uses LLVM API, so it doesn't recognize this option even though it may be valid for llc.

[Mark-Simulacrum]

I'm going to close in favor of #26338, since I agree that issue is the real cause of this one.