possible to compile libstd with full MIR:
```sh
+rustup component add rust-src
+chmod +x -R ~/.rustup/toolchains/*/lib/rustlib/src/rust/src/jemalloc/include/jemalloc/
cargo install xargo
cd xargo/
RUSTFLAGS='-Zalways-encode-mir' xargo build --target `rustc -vV | egrep '^host: ' | sed 's/^host: //'`
```
Notice that you will have to re-run the last step of the preparations above when
-your toolchain changes (e.g., when you update the nightly). Also, xargo doesn't
-currently work with nightlies newer than 2017-04-23.
+your toolchain changes (e.g., when you update the nightly).
## Contributing and getting help