Avoid realloc in CString::new
#65551
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r? @Kimundi (rust_highfive has picked a reviewer for you, use r? to override) |
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cc #35838 |
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r? @eddyb |
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LGTM but this is a libs change, cc @alexcrichton @sfackler. |
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@bors r+ |
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📌 Commit 23cb1d5 has been approved by |
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Centril
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Avoid realloc in `CString::new` If `&[u8]` or `&str` is given, `CString::new` allocates a new `Vec` with the exact capacity, and then `CString::from_vec_unchecked` calls `.reserve_exact(1)` for nul byte. This PR avoids the reallocation by allocationg `len + 1` bytes beforehand. In microbenchmark this PR speeds up `CString::new(&[u8])` by 30%.
Centril
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Oct 20, 2019
Avoid realloc in `CString::new` If `&[u8]` or `&str` is given, `CString::new` allocates a new `Vec` with the exact capacity, and then `CString::from_vec_unchecked` calls `.reserve_exact(1)` for nul byte. This PR avoids the reallocation by allocationg `len + 1` bytes beforehand. In microbenchmark this PR speeds up `CString::new(&[u8])` by 30%.
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Oct 20, 2019
Rollup of 6 pull requests Successful merges: - #64996 (Inline `ptr::null(_mut)` even in debug builds) - #65551 (Avoid realloc in `CString::new`) - #65593 (add test for calling non-const fn) - #65595 (move `parse_cfgspecs` to `rustc_interface`) - #65600 (Remove unneeded `ref` from docs) - #65602 (Fix plural mistake in emitter.rs) Failed merges: r? @ghost
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If
&[u8]or&stris given,CString::newallocates a newVecwith the exact capacity, and thenCString::from_vec_uncheckedcalls.reserve_exact(1)for nul byte. This PR avoids the reallocation by allocationglen + 1bytes beforehand. In microbenchmark this PR speeds upCString::new(&[u8])by 30%.