`-Zthreads` changes compiled binary

[matthiaskrgr]

rustc 1.75.0-nightly (e1fcecb1b 2023-11-06)
binary: rustc
commit-hash: e1fcecb1b9930f109a8c1cf2b690e03483a41289
commit-date: 2023-11-06
host: x86_64-unknown-linux-gnu
release: 1.75.0-nightly
LLVM version: 17.0.4

reproducible with both cargo and oxipng

1. cargo build --release
   => 1816 target/release/oxipng (du -sk)
2. RUSTFLAGS="-Zthreads=1" cargo build --release
   => 1692 target/release/oxipng

seems that Zthreads on/off has an effect on the generated binary 🤔

[lqd]

(note: the default is -Zthreads=1)

[saethlin]

I cannot reproduce this with oxipng. I get exactly the same binary with or without -Zthreads=1.

[lqd]

@matthiaskrgr do you have global flags / cargo configs, that would be turned off when manually overriding RUSTFLAGS in your second example ?

[matthiaskrgr]

OOoh yes, I totally forgot I had RUSTFLAGS="-march=native" exported via my bash rc. :D

[matthiaskrgr]

I was already wondering why I could not reproduce this when calling rustc via a script (where RUSTFLAGS is always overridden...) lol

Sorry for the noise :D

[lqd]

my disappointment is immeasurable and my day is ruined :3