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         return;
  20     }
  21     let arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
  22     match &arch[..] {
  23         "x86_64" => {
  24             if !target_has_feature("sse2") {
  25                 return;
  26             }
  27             println!("cargo:rustc-cfg=memchr_runtime_simd");
  28             println!("cargo:rustc-cfg=memchr_runtime_sse2");
  29             println!("cargo:rustc-cfg=memchr_runtime_sse42");
  30             println!("cargo:rustc-cfg=memchr_runtime_avx");
  31         }
  32         "wasm32" | "wasm64" => {
  33             if !target_has_feature("simd128") {
  34                 return;
  35             }
  36             println!("cargo:rustc-cfg=memchr_runtime_simd");
  37             println!("cargo:rustc-cfg=memchr_runtime_wasm128");
  38         }
  39         _ => {}
  40     }
  41 }
  42
  43 // This adds a `memchr_libc` cfg if and only if libc can be used, if no other
  44 // better option is available.
  45 //
  46 // This could be performed in the source code, but it's simpler to do it once
  47 // here and consolidate it into one cfg knob.
  48 //
  49 // Basically, we use libc only if its enabled and if we aren't targeting a
  50 // known bad platform. For example, wasm32 doesn't have a libc and the
  51 // performance of memchr on Windows is seemingly worse than the fallback
  52 // implementation.
  53 fn enable_libc() {
  54     const NO_ARCH: &'static [&'static str] = &["wasm32", "windows"];
  55     const NO_ENV: &'static [&'static str] = &["sgx"];
  56
  57     if !is_feature_set("LIBC") {
  58         return;
  59     }
  60
  61     let arch = match env::var("CARGO_CFG_TARGET_ARCH") {
  62         Err(_) => return,
  63         Ok(arch) => arch,
  64     };
  65     let env = match env::var("CARGO_CFG_TARGET_ENV") {
  66         Err(_) => return,
  67         Ok(env) => env,
  68     };
  69     if NO_ARCH.contains(&&*arch) || NO_ENV.contains(&&*env) {
  70         return;
  71     }
  72
  73     println!("cargo:rustc-cfg=memchr_libc");
  74 }
  75
  76 fn is_feature_set(name: &str) -> bool {
  77     is_env_set(&format!("CARGO_FEATURE_{}", name))
  78 }
  79
  80 fn is_env_set(name: &str) -> bool {
  81     env::var_os(name).is_some()
  82 }
  83
  84 fn target_has_feature(feature: &str) -> bool {
  85     env::var("CARGO_CFG_TARGET_FEATURE")
  86         .map(|features| features.contains(feature))
  87         .unwrap_or(false)
  88 }