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Auto merge of #88988 - Mark-Simulacrum:avoid-into-ok, r=nagisa

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Avoid codegen for Result::into_ok in lang_start

This extra codegen seems to be the cause for the regressions in max-rss on #86034. While LLVM will certainly optimize the dead code away, avoiding it's generation in the first place seems good, particularly when it is so simple.

#86034 produced this [diff](https://gist.github.com/Mark-Simulacrum/95c7599883093af3b960c35ffadf4dab#file-86034-diff) for a simple `fn main() {}`. With this PR, that diff [becomes limited to just a few extra IR instructions](https://gist.github.com/Mark-Simulacrum/95c7599883093af3b960c35ffadf4dab#file-88988-from-pre-diff) -- no extra functions.

Note that these are pre-optimization; LLVM surely will eliminate this during optimization. However, that optimization can end up generating more work and bump memory usage, and this eliminates that.
This commit is contained in:
bors 2021-09-18 09:15:40 +00:00
commit 6cdd42f9f8
1 changed files with 3 additions and 3 deletions
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6
library/std/src/rt.rs
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@ -60,10 +60,10 @@ fn lang_start<T: crate::process::Termination + 'static>(
argc: isize, argc: isize,
argv: *const *const u8, argv: *const *const u8,
) -> isize { ) -> isize {
lang_start_internal( let Ok(v) = lang_start_internal(
&move || crate::sys_common::backtrace::__rust_begin_short_backtrace(main).report(), &move || crate::sys_common::backtrace::__rust_begin_short_backtrace(main).report(),
argc, argc,
argv, argv,
) );
.into_ok() v
} }