1 files changed, 88 insertions, 0 deletions
diff --git a/third_party/rust/memchr/build.rs b/third_party/rust/memchr/build.rs
new file mode 100644
index 0000000000..584a608565
--- /dev/null
+++ b/third_party/rust/memchr/build.rs
@@ -0,0 +1,88 @@
+use std::env;
+
+fn main() {
+    enable_simd_optimizations();
+    enable_libc();
+}
+
+// This adds various simd cfgs if this compiler and target support it.
+//
+// This can be disabled with RUSTFLAGS="--cfg memchr_disable_auto_simd", but
+// this is generally only intended for testing.
+//
+// On targets which don't feature SSE2, this is disabled, as LLVM wouln't know
+// how to work with SSE2 operands. Enabling SSE4.2 and AVX on SSE2-only targets
+// is not a problem. In that case, the fastest option will be chosen at
+// runtime.
+fn enable_simd_optimizations() {
+    if is_env_set("CARGO_CFG_MEMCHR_DISABLE_AUTO_SIMD") {
+        return;
+    }
+    let arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
+    match &arch[..] {
+        "x86_64" => {
+            if !target_has_feature("sse2") {
+                return;
+            }
+            println!("cargo:rustc-cfg=memchr_runtime_simd");
+            println!("cargo:rustc-cfg=memchr_runtime_sse2");
+            println!("cargo:rustc-cfg=memchr_runtime_sse42");
+            println!("cargo:rustc-cfg=memchr_runtime_avx");
+        }
+        "wasm32" | "wasm64" => {
+            if !target_has_feature("simd128") {
+                return;
+            }
+            println!("cargo:rustc-cfg=memchr_runtime_simd");
+            println!("cargo:rustc-cfg=memchr_runtime_wasm128");
+        }
+        _ => {}
+    }
+}
+
+// This adds a `memchr_libc` cfg if and only if libc can be used, if no other
+// better option is available.
+//
+// This could be performed in the source code, but it's simpler to do it once
+// here and consolidate it into one cfg knob.
+//
+// Basically, we use libc only if its enabled and if we aren't targeting a
+// known bad platform. For example, wasm32 doesn't have a libc and the
+// performance of memchr on Windows is seemingly worse than the fallback
+// implementation.
+fn enable_libc() {
+    const NO_ARCH: &'static [&'static str] = &["wasm32", "windows"];
+    const NO_ENV: &'static [&'static str] = &["sgx"];
+
+    if !is_feature_set("LIBC") {
+        return;
+    }
+
+    let arch = match env::var("CARGO_CFG_TARGET_ARCH") {
+        Err(_) => return,
+        Ok(arch) => arch,
+    };
+    let env = match env::var("CARGO_CFG_TARGET_ENV") {
+        Err(_) => return,
+        Ok(env) => env,
+    };
+    if NO_ARCH.contains(&&*arch) || NO_ENV.contains(&&*env) {
+        return;
+    }
+
+    println!("cargo:rustc-cfg=memchr_libc");
+}
+
+fn is_feature_set(name: &str) -> bool {
+    is_env_set(&format!("CARGO_FEATURE_{}", name))
+}
+
+fn is_env_set(name: &str) -> bool {
+    env::var_os(name).is_some()
+}
+
+fn target_has_feature(feature: &str) -> bool {
+    env::var("CARGO_CFG_TARGET_FEATURE")
+        .map(|features| features.contains(feature))
+        .unwrap_or(false)
+}