A couple micro-optimizations of Vec and std::io::me::* #15068
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Generally speaking, inlining doesn't really help out with constructing vectors, except for when we construct a zero-sized vector. This patch allows llvm to optimize this case away in a lot of cases, which shaves off 4-8ns. It's not much, but it might help in some inner loop somewhere. before: running 12 tests test bench_extend_0 ... bench: 123 ns/iter (+/- 6) test bench_extend_5 ... bench: 323 ns/iter (+/- 11) test bench_from_fn_0 ... bench: 7 ns/iter (+/- 0) test bench_from_fn_5 ... bench: 49 ns/iter (+/- 6) test bench_from_iter_0 ... bench: 11 ns/iter (+/- 0) test bench_from_iter_5 ... bench: 176 ns/iter (+/- 11) test bench_from_slice_0 ... bench: 8 ns/iter (+/- 1) test bench_from_slice_5 ... bench: 73 ns/iter (+/- 5) test bench_new ... bench: 0 ns/iter (+/- 0) test bench_with_capacity_0 ... bench: 6 ns/iter (+/- 1) test bench_with_capacity_100 ... bench: 41 ns/iter (+/- 3) test bench_with_capacity_5 ... bench: 40 ns/iter (+/- 2) after: test bench_extend_0 ... bench: 123 ns/iter (+/- 7) test bench_extend_5 ... bench: 339 ns/iter (+/- 27) test bench_from_fn_0 ... bench: 7 ns/iter (+/- 0) test bench_from_fn_5 ... bench: 54 ns/iter (+/- 4) test bench_from_iter_0 ... bench: 11 ns/iter (+/- 1) test bench_from_iter_5 ... bench: 182 ns/iter (+/- 16) test bench_from_slice_0 ... bench: 4 ns/iter (+/- 0) test bench_from_slice_5 ... bench: 62 ns/iter (+/- 3) test bench_new ... bench: 0 ns/iter (+/- 0) test bench_with_capacity_0 ... bench: 0 ns/iter (+/- 0) test bench_with_capacity_100 ... bench: 41 ns/iter (+/- 1) test bench_with_capacity_5 ... bench: 41 ns/iter (+/- 3)
This allows llvm to optimize away much of the overhead from using the MemReader/MemWriters. My benchmarks showed it to shave 15% off of my in progress serialization/json encoding.
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This is a couple micro-optimizations I've been sitting on for a while. This inlines a couple functions that are important to the `std::io::mem`. Ultimately, this results in about a 15% performance increase in some micro-benchmarks for my [libserialize](https://github.com/erickt/rust-serde) rewrite.
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This is a couple micro-optimizations I've been sitting on for a while. This inlines a couple functions that are important to the
std::io::mem. Ultimately, this results in about a 15% performance increase in some micro-benchmarks for my libserialize rewrite.