29a946203a
std/sys/unix/time: make it easier for LLVM to optimize `Instant` subtraction. This PR is the minimal change necessary to get LLVM to optimize `if self.t.tv_nsec >= other.t.tv_nsec` to branchless instructions (at least on x86_64), inspired by @m-ou-se's own attempts at optimizing `Instant` subtraction. I stumbled over this by looking at the total number of instructions executed by `rustc -Z self-profile`, and found that after disabling ASLR, the largest source of non-determinism remaining was from this `if` taking one branch or the other, depending on the values involved. The reason this code is even called so many times to make a difference, is that `measureme` (the `-Z self-profile` implementation) currently uses `Instant::elapsed` for its event timestamps (of which there can be millions). I doubt it's critical to land this, although perhaps it could slightly improve some forms of benchmarking. |
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| benches | ||
| src | ||
| tests | ||
| build.rs | ||
| Cargo.toml | ||