Don't emit divide-by-zero panic paths in StepBy::len
#123564
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I happened to notice today that there's actually two such calls emitted in the assembly: <https://rust.godbolt.org/z/1Wbbd3Ts6> Since they're impossible, hopefully telling LLVM that will also help optimizations elsewhere.
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scottmcm
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Apr 6, 2024
| iter: &mut I, | ||
| step_minus_one: usize, | ||
| ) -> impl FnMut() -> Option<I::Item> + '_ { | ||
| move || iter.nth(step_minus_one) |
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As I went through I also tried to be consistent about naming things step_minus_one when they're not the original step, since it was confusing to have the mix.
scottmcm
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Apr 6, 2024
| @@ -500,7 +518,7 @@ macro_rules! spec_int_ranges_r { | |||
| fn spec_next_back(&mut self) -> Option<Self::Item> | |||
| where Range<$t>: DoubleEndedIterator + ExactSizeIterator, | |||
| { | |||
| let step = (self.step + 1) as $t; | |||
| let step = self.original_step().get() as $t; | |||
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Like how here the two steps in the previous code meant very different things, but since the let step is the width (not the "what to pass to nth") it's still called step.
scottmcm
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Apr 6, 2024
| fn first_size(step: usize) -> impl Fn(usize) -> usize { | ||
| move |n| if n == 0 { 0 } else { 1 + (n - 1) / (step + 1) } | ||
| fn first_size(step: NonZeroUsize) -> impl Fn(usize) -> usize { | ||
| move |n| if n == 0 { 0 } else { 1 + (n - 1) / step } |
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Thank you, Div<NonZeroUsize>, for just magically doing the right thing here 🎉
joboet
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Apr 8, 2024
|
@bors r+ |
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…iaskrgr Rollup of 9 pull requests Successful merges: - rust-lang#122781 (Fix argument ABI for overaligned structs on ppc64le) - rust-lang#123367 (Safe Transmute: Compute transmutability from `rustc_target::abi::Layout`) - rust-lang#123518 (Fix `ByMove` coroutine-closure shim (for 2021 precise closure capturing behavior)) - rust-lang#123547 (bootstrap: remove unused pub fns) - rust-lang#123564 (Don't emit divide-by-zero panic paths in `StepBy::len`) - rust-lang#123578 (Restore `pred_known_to_hold_modulo_regions`) - rust-lang#123591 (Remove unnecessary cast from `LLVMRustGetInstrProfIncrementIntrinsic`) - rust-lang#123632 (parser: reduce visibility of unnecessary public `UnmatchedDelim`) - rust-lang#123635 (CFI: Fix ICE in KCFI non-associated function pointers) r? `@ghost` `@rustbot` modify labels: rollup
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Rollup merge of rust-lang#123564 - scottmcm:step-by-div-zero, r=joboet Don't emit divide-by-zero panic paths in `StepBy::len` I happened to notice today that there's actually two such calls emitted in the assembly: <https://rust.godbolt.org/z/1Wbbd3Ts6> Since they're impossible, hopefully telling LLVM that will also help optimizations elsewhere.
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I happened to notice today that there's actually two such calls emitted in the assembly: https://rust.godbolt.org/z/1Wbbd3Ts6
Since they're impossible, hopefully telling LLVM that will also help optimizations elsewhere.