Reduce code size overhead from core::panicking::panic #22948
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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @brson (or someone else) soon. If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. The way Github handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes. Please see CONTRIBUTING.md for more information. |
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LGTM, but I think this test case doesn't capture anything new, so please remove it. @alexcrichton are you ok adding an unstable method to the ArgumentsV1 trait here? |
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Couldn't this call Either way, can you add documentation to |
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I had added this short comment inside // To reduce formatting code size overhead, create an Arguments structure
// that does not reference a formatting function.I'll remove the test. |
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Yeah that's fine, thanks! |
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Let me know if I should squash and/or rebase these changes. |
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Ah yes, a squash would be nice, other than that r=me, this looks great, thanks! |
Display::fmt for str calls into Formatter::pad, which is modest in size and also pulls in string-related functions for its truncation and padding abilities. For size-critical programs (e.g. embedded), this call site may be the only reason Formatter::pad is linked into the output.
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@alexcrichton I squashed the commits, so this PR should be ready now. |
Reduce code size overhead from core::panicking::panic
core::panicking::panic currently creates an Arguments structure using
format_args!("{}", expr), which formats the expr str using the Display::fmt.
Display::fmt pulls in Formatter::pad, which then also pulls in string-related
code for truncation and padding.
If core::panicking::panic instead creates an Arguments structure with a string
piece, it is possible that the Display::fmt function for str can be optimized
out of the program.
In my testing with a 32-bit x86 bare metal program, the change tended to save
between ~100 bytes and ~5500 bytes, depending on what other panic* functions
the program invokes and whether the panic_fmt lang item uses the Arguments
value.
Reduce code size overhead from core::panicking::panic
core::panicking::panic currently creates an Arguments structure using
format_args!("{}", expr), which formats the expr str using the Display::fmt.
Display::fmt pulls in Formatter::pad, which then also pulls in string-related
code for truncation and padding.
If core::panicking::panic instead creates an Arguments structure with a string
piece, it is possible that the Display::fmt function for str can be optimized
out of the program.
In my testing with a 32-bit x86 bare metal program, the change tended to save
between ~100 bytes and ~5500 bytes, depending on what other panic* functions
the program invokes and whether the panic_fmt lang item uses the Arguments
value.