Reduce the amount of code that fail!() creates #11841
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This splits the vast majority of the code path taken by `fail!()` (`begin_unwind`) into a separate non-generic inline(never) function, so that uses of `fail!()` only monomorphise a small amount of code, reducing code bloat and making very small crates compile faster.
This ends up saving a single `call` instruction in the optimised code,
but saves a few hundred lines of non-optimised IR for `fn main() {
fail!("foo {}", "bar"); }` (comparing against the minimal generic
baseline from the parent commit).
| /// the actual formatting into this shared place. | ||
| #[inline(never)] #[cold] | ||
| pub fn begin_unwind_fmt(msg: &fmt::Arguments, file: &'static str, line: uint) -> ! { | ||
| begin_unwind_inner(~fmt::format(msg), file, line) |
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Could you add a comment referencing the comment below just explaining why it's "ok" we're doing two allocations here?
bors
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In two ways:
- for a plain `fail!(a)` we make the generic part of `begin_unwind` as small as possible (makes `fn main() { fail!() }` compile 2-3x faster, due to less monomorphisation bloat)
- for `fail!("format {}", "string")`, we avoid touching the generics completely by doing the formatting in a specialised function, which (with optimisations) saves a function call at the call-site of `fail!`. (This one has significantly less benefit than the first.)
bors
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Jan 27, 2014
In two ways:
- for a plain `fail!(a)` we make the generic part of `begin_unwind` as small as possible (makes `fn main() { fail!() }` compile 2-3x faster, due to less monomorphisation bloat)
- for `fail!("format {}", "string")`, we avoid touching the generics completely by doing the formatting in a specialised function, which (with optimisations) saves a function call at the call-site of `fail!`. (This one has significantly less benefit than the first.)
huonw
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Jan 28, 2014
Follow-up to rust-lang#11841 which added this function.
bors
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Jan 28, 2014
Follow-up to #11841 which added this function.
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In two ways:
fail!(a)we make the generic part ofbegin_unwindas small as possible (makesfn main() { fail!() }compile 2-3x faster, due to less monomorphisation bloat)fail!("format {}", "string"), we avoid touching the generics completely by doing the formatting in a specialised function, which (with optimisations) saves a function call at the call-site offail!. (This one has significantly less benefit than the first.)