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Reorder lto options in profiles.md #15841

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Aug 17, 2025
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Reorder lto options in profiles.md #15841

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Reorder `lto` options in profiles.md
smoelius Aug 15, 2025
396f8c6
Mention ordering rationale in profiles.md
smoelius Aug 17, 2025
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Mention ordering rationale in profiles.md 
Co-authored-by: Weihang Lo <[email protected]>
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@smoelius @weihanglo
smoelius and weihanglo authored Aug 17, 2025
commit 396f8c62ed0242442d5004ffe605dfea9d5f9907
2 changes: 1 addition & 1 deletion src/doc/src/reference/profiles.md
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Expand Up @@ -166,7 +166,7 @@ The `lto` setting controls `rustc`'s [`-C lto`], [`-C linker-plugin-lto`], and
LTO can produce better optimized code, using whole-program analysis, at the cost
of longer linking time.

The valid options are:
The valid options from most to least optimizing are:
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As I understand it, this is not true in the general case. fat LTO can produce faster executables than ThinLTO and even if it doesn't, it is often very close. ThinLTO just generally produces a bit bigger executables.

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So in terms of executable performance,

is it fat >= ThinLTO or ThinLTO >= fat, or hard to say?

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@bjorn3 bjorn3 Aug 17, 2025 •
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As I understand it, it could be either way nowadays. There is probably still some bias for fat LTO producing faster executables than ThinLTO though.

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I see. Thanks for pointing it out!

There is another similar ongoing in rust-lang/rust rust-lang/rust#145533. Do you think we should r- that, and revert this PR as well?

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I think the order makes sense. I just think we should not explicitly say "from most to least optimizing" here.


* `true` or `"fat"`: Performs "fat" LTO which attempts to perform
optimizations across all crates within the dependency graph.
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