León Orell Valerian Liehr 4f7d9d4ad8 Rollup merge of #125038 - ivan-shrimp:checked_sub, r=joboet ... Invert comparison in `uN::checked_sub` After #124114, LLVM no longer combines the comparison and subtraction in `uN::checked_sub` when either operand is a constant (demo: https://rust.godbolt.org/z/MaeoYbsP1). The difference is more pronounced when the expression is slightly more complex (https://rust.godbolt.org/z/4rPavsYdc). This is due to the use of `>=` here: ee97564e3a/library/core/src/num/uint_macros.rs (L581-L593) For constant `C`, LLVM eagerly converts `a >= C` into `a > C - 1`, but the backend can only combine `a < C` with `a - C`, not `C - 1 < a` and `a - C`: e586556e37/llvm/lib/CodeGen/CodeGenPrepare.cpp (L1697-L1742) This PR[^1] simply inverts the `>=` into `<` to restore the LLVM magic, and somewhat align this with the implementation of `uN::overflowing_sub` from #103299. When the result is stored as an `Option` (rather than being branched/cmoved on), the discriminant is `self >= rhs`. This PR doesn't affect the codegen (and relevant tests) of that since LLVM will negate `self < rhs` to `self >= rhs` when necessary. [^1]: Note to `self`: My very first contribution to publicly-used code. Hopefully like what I should learn to always be, tiny and humble.		2024-05-15 14:21:38 +02:00
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benches	Add benchmarks for impl Debug for str	2024-05-01 09:54:29 +02:00
src	Rollup merge of #125038 - ivan-shrimp:checked_sub, r=joboet	2024-05-15 14:21:38 +02:00
tests	Step bootstrap cfgs	2024-05-01 22:19:11 -04:00
Cargo.toml	Import the 2021 prelude in the core crate	2024-03-25 13:12:06 -07:00