Add a "host" crate for autodetecting the host. (#159)

* Add a "native" crate for autodetecting the host.

* Remove the redundant .gitignore.

* Use the proper builder for enabling subtarget flags.

lib/native/src/lib.rs

@@ -0,0 +1,88 @@
+//! Performs autodetection of the host for the purposes of running
+//! Cretonne to generate code to run on the same machine.
+
+#![deny(missing_docs)]
+
+extern crate cretonne;
+
+#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+extern crate raw_cpuid;
+
+use cretonne::isa;
+use cretonne::settings::{self, Configurable};
+
+#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+use raw_cpuid::CpuId;
+
+/// Return `settings` and `isa` builders configured for the current host
+/// machine, or `Err(())` if the host machine is not supported
+/// in the current configuration.
+pub fn builders() -> Result<(settings::Builder, isa::Builder), ()> {
+    let mut flag_builder = settings::builder();
+
+    // TODO: Add RISC-V support once Rust supports it.
+
+    if cfg!(target_pointer_width = "64") {
+        flag_builder.enable("is_64bit").unwrap();
+    }
+
+    let name = if cfg!(any(target_arch = "x86", target_arch = "x86_64")) {
+        "intel"
+    } else if cfg!(target_arch = "arm") {
+        "arm32"
+    } else if cfg!(target_arch = "aarch64") {
+        "arm64"
+    } else {
+        return Err(());
+    };
+
+    let mut isa_builder = isa::lookup(name).map_err(|err| match err {
+        isa::LookupError::Unknown => panic!(),
+        isa::LookupError::Unsupported => (()),
+    })?;
+
+    if cfg!(any(target_arch = "x86", target_arch = "x86_64")) {
+        parse_x86_cpuid(&mut isa_builder);
+    }
+
+    Ok((flag_builder, isa_builder))
+}
+
+#[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+fn parse_x86_cpuid(isa_builder: &mut isa::Builder) {
+    let cpuid = CpuId::new();
+
+    if let Some(info) = cpuid.get_feature_info() {
+        if info.has_sse2() {
+            isa_builder.enable("has_sse2").unwrap();
+        }
+        if info.has_sse3() {
+            isa_builder.enable("has_sse3").unwrap();
+        }
+        if info.has_sse41() {
+            isa_builder.enable("has_sse41").unwrap();
+        }
+        if info.has_sse42() {
+            isa_builder.enable("has_sse42").unwrap();
+        }
+        if info.has_popcnt() {
+            isa_builder.enable("has_popcnt").unwrap();
+        }
+        if info.has_avx() {
+            isa_builder.enable("has_avx").unwrap();
+        }
+    }
+    if let Some(info) = cpuid.get_extended_feature_info() {
+        if info.has_bmi1() {
+            isa_builder.enable("has_bmi1").unwrap();
+        }
+        if info.has_bmi2() {
+            isa_builder.enable("has_bmi2").unwrap();
+        }
+    }
+    if let Some(info) = cpuid.get_extended_function_info() {
+        if info.has_lzcnt() {
+            isa_builder.enable("has_lzcnt").unwrap();
+        }
+    }
+}