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Optimize build for libbz2.a #88

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Optimize build for libbz2.a #88

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f8d1029
Use `--gc-sections` to remove unused symbols from `libbz2.a`
NobodyXu Jan 27, 2023
e952617
Add new feature `fat-lto` & `thin-lto`
NobodyXu Jan 27, 2023
0f8f115
Add new feat `thin` to use opt-level `z`
NobodyXu Jan 28, 2023
814695e
Remove unused `-Wl` linker args
NobodyXu Feb 1, 2023
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5 changes: 5 additions & 0 deletions Cargo.toml
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Expand Up @@ -33,3 +33,8 @@ tokio-core = "0.1"
tokio = ["tokio-io", "futures"]
# Enable this feature if you want to have a statically linked bzip2
static = ["bzip2-sys/static"]

fat-lto = ["bzip2-sys/fat-lto"]
thin-lto = ["bzip2-sys/thin-lto"]

thin = ["bzip2-sys/thin"]
5 changes: 5 additions & 0 deletions bzip2-sys/Cargo.toml
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Expand Up @@ -28,3 +28,8 @@ cc = "1.0"
[features]
# Enable this feature if you want to have a statically linked bzip2
static = []

fat-lto = [] # Enable fat-lto, will override thin-lto if specified
thin-lto = [] # Enable thin-lto, will fallback to fat-lto if not supported

thin = [] # Use -Oz is possible, otherwise fallback to -Os or -O2. For msvc it will be /O1
20 changes: 20 additions & 0 deletions bzip2-sys/build.rs
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Expand Up @@ -25,6 +25,26 @@ fn main() {

let dst = PathBuf::from(env::var_os("OUT_DIR").unwrap());

cfg.flag_if_supported("-ffunction-sections")
.flag_if_supported("-fdata-sections")
.flag_if_supported("-fmerge-all-constants")
.flag_if_supported("-Wl,--gc-sections")
.flag_if_supported("-Wl,--icf=safe");
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Makes sense to have -ffunction-sections and co. -Wl,--gc-sections and -Wl,--icf=safe can be omitted though as those only apply to linking by the cc crate, but we only build a staticlib here. They don't have any effect on linking done by rustc.


if cfg!(feature = "fat-lto") {
cfg.flag_if_supported("-flto");
} else if cfg!(feature = "thin-lto") {
if cfg.is_flag_supported("-flto=thin").unwrap_or(false) {
cfg.flag("-flto=thin");
} else {
cfg.flag_if_supported("-flto");
}
}
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I've asked at https://rust-lang.zulipchat.com/#narrow/channel/246057-t-cargo/topic/read.20lto.20config.20from.20build.20script if there is a way to read the LTO state from cargo without having to use feature flags. In any case this won't actually LTO between bzip2 and any rust code. That is only possible when using the rust port of bzip2 rather than the C original or by using -Clinker-plugin-lto and making sure that the exact right clang version is used to build the C code.

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Turns out the cc crate itself nowadays handles -Clto and -Copt-level already, so the second and third commit can be dropped. Only the first and fourth commit (which should be squashed) are still necessary.


if cfg!(feature = "thin") {
cfg.opt_level_str("z");
}
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This should probably forward the OPT_LEVEL env var instead of adding a feature.


cfg.include("bzip2-1.0.8")
.define("_FILE_OFFSET_BITS", Some("64"))
.define("BZ_NO_STDIO", None)
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