vendor/memchr/build.rs

   1 use std::env;
   2
   3 fn main() {
   4     enable_simd_optimizations();
   5     enable_libc();
   6 }
   7
   8 // This adds various simd cfgs if this compiler and target support it.
   9 //
  10 // This can be disabled with RUSTFLAGS="--cfg memchr_disable_auto_simd", but
  11 // this is generally only intended for testing.
  12 //
  13 // On targets which don't feature SSE2, this is disabled, as LLVM wouln't know
  14 // how to work with SSE2 operands. Enabling SSE4.2 and AVX on SSE2-only targets
  15 // is not a problem. In that case, the fastest option will be chosen at
  16 // runtime.
  17 fn enable_simd_optimizations() {
  18     if is_env_set("CARGO_CFG_MEMCHR_DISABLE_AUTO_SIMD")
  19         || !target_has_feature("sse2")
  20     {
  21         return;
  22     }
  23     println!("cargo:rustc-cfg=memchr_runtime_simd");
  24     println!("cargo:rustc-cfg=memchr_runtime_sse2");
  25     println!("cargo:rustc-cfg=memchr_runtime_sse42");
  26     println!("cargo:rustc-cfg=memchr_runtime_avx");
  27 }
  28
  29 // This adds a `memchr_libc` cfg if and only if libc can be used, if no other
  30 // better option is available.
  31 //
  32 // This could be performed in the source code, but it's simpler to do it once
  33 // here and consolidate it into one cfg knob.
  34 //
  35 // Basically, we use libc only if its enabled and if we aren't targeting a
  36 // known bad platform. For example, wasm32 doesn't have a libc and the
  37 // performance of memchr on Windows is seemingly worse than the fallback
  38 // implementation.
  39 fn enable_libc() {
  40     const NO_ARCH: &'static [&'static str] = &["wasm32", "windows"];
  41     const NO_ENV: &'static [&'static str] = &["sgx"];
  42
  43     if !is_feature_set("LIBC") {
  44         return;
  45     }
  46
  47     let arch = match env::var("CARGO_CFG_TARGET_ARCH") {
  48         Err(_) => return,
  49         Ok(arch) => arch,
  50     };
  51     let env = match env::var("CARGO_CFG_TARGET_ENV") {
  52         Err(_) => return,
  53         Ok(env) => env,
  54     };
  55     if NO_ARCH.contains(&&*arch) || NO_ENV.contains(&&*env) {
  56         return;
  57     }
  58
  59     println!("cargo:rustc-cfg=memchr_libc");
  60 }
  61
  62 fn is_feature_set(name: &str) -> bool {
  63     is_env_set(&format!("CARGO_FEATURE_{}", name))
  64 }
  65
  66 fn is_env_set(name: &str) -> bool {
  67     env::var_os(name).is_some()
  68 }
  69
  70 fn target_has_feature(feature: &str) -> bool {
  71     env::var("CARGO_CFG_TARGET_FEATURE")
  72         .map(|features| features.contains(feature))
  73         .unwrap_or(false)
  74 }