Fixes #13: Enable conditional compilation of ISAs through features;

cranelift/codegen/Cargo.toml

@@ -29,16 +29,24 @@ log = { version = "0.4.6", default-features = false }
 cranelift-codegen-meta = { path = "meta", version = "0.28.0" }
 
 [features]
+default = ["std", "x86", "arm32", "arm64", "riscv"]
+
 # The "std" feature enables use of libstd. The "core" feature enables use
 # of some minimal std-like replacement libraries. At least one of these two
 # features need to be enabled.
-default = ["std"]
 std = ["cranelift-entity/std", "cranelift-bforest/std", "target-lexicon/std"]
 core = ["hashmap_core"]
+
 # This enables some additional functions useful for writing tests, but which
 # can significantly increase the size of the library.
 testing_hooks = []
 
+# ISA targets for which we should build.
+x86 = []
+arm32 = []
+arm64 = []
+riscv = []
+
 [badges]
 maintenance = { status = "experimental" }
 travis-ci = { repository = "CraneStation/cranelift" }

cranelift/codegen/build.rs

@@ -11,10 +11,6 @@
 // TARGET
 //     Target triple provided by Cargo.
 //
-// CRANELIFT_TARGETS (Optional)
-//     A setting for conditional compilation of isa targets. Possible values can be "native" or
-//     known isa targets separated by ','.
-//
 // The build script expects to be run from the directory where this build.rs file lives. The
 // current directory is used to find the sources.
 
@@ -31,22 +27,24 @@ fn main() {
     let target_triple = env::var("TARGET").expect("The TARGET environment variable must be set");
 
     // Configure isa targets cfg.
-    let cranelift_targets = env::var("CRANELIFT_TARGETS").ok();
-    let cranelift_targets = cranelift_targets
-        .as_ref()
-        .map(|s| s.as_ref())
-        .filter(|s: &&str| s.len() > 0);
+    let isa_targets = meta::isa::Isa::all()
+        .into_iter()
+        .cloned()
+        .filter(|isa| {
+            let env_key = format!("CARGO_FEATURE_{}", isa.to_string().to_uppercase());
+            env::var(env_key).is_ok()
+        })
+        .collect::<Vec<_>>();
 
-    let isas = match cranelift_targets {
-        Some("native") => meta::isa_from_arch(&target_triple.split('-').next().unwrap()),
-        Some(targets) => meta::isas_from_targets(targets.split(',').collect::<Vec<_>>()),
-        None => meta::all_isas(),
-    }
-    .expect("Error when identifying CRANELIFT_TARGETS and TARGET");
-
-    for isa in &isas {
-        println!("cargo:rustc-cfg=build_{}", isa.to_string());
-    }
+    let isas = if isa_targets.is_empty() {
+        // Try to match native target.
+        let target_name = target_triple.split('-').next().unwrap();
+        let isa = meta::isa_from_arch(&target_name).expect("error when identifying target");
+        println!("cargo:rustc-cfg=feature=\"{}\"", isa);
+        vec![isa]
+    } else {
+        isa_targets
+    };
 
     let cur_dir = env::current_dir().expect("Can't access current working directory");
     let crate_dir = cur_dir.as_path();

cranelift/codegen/meta/src/isa/mod.rs

@@ -44,6 +44,7 @@ impl Isa {
 }
 
 impl fmt::Display for Isa {
+    // These names should be kept in sync with the crate features.
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             Isa::Riscv => write!(f, "riscv"),

cranelift/codegen/meta/src/lib.rs

@@ -13,43 +13,8 @@ mod shared;
 mod srcgen;
 mod unique_table;
 
-pub fn isa_from_arch(arch: &str) -> Result<Vec<isa::Isa>, String> {
-    isa::Isa::from_arch(arch)
-        .ok_or_else(|| format!("no supported isa found for arch `{}`", arch))
-        .and_then(|isa| Ok(vec![isa]))
-}
-
-pub fn isas_from_targets(targets: Vec<&str>) -> Result<Vec<isa::Isa>, String> {
-    type R<'a> = Vec<(&'a str, Option<isa::Isa>)>;
-
-    let (known, unknown): (R, R) = targets
-        .into_iter()
-        .map(|target| (target, isa::Isa::from_name(target)))
-        .partition(|(_, opt_isa)| opt_isa.is_some());
-
-    if !unknown.is_empty() {
-        let unknown_targets = unknown
-            .into_iter()
-            .map(|(target, _)| target)
-            .collect::<Vec<_>>()
-            .join(", ");
-        return Err(format!("unknown isa targets: {}", unknown_targets));
-    }
-
-    let isas = if known.is_empty() {
-        isa::Isa::all().to_vec()
-    } else {
-        known
-            .into_iter()
-            .map(|(_, opt_isa)| opt_isa.unwrap())
-            .collect()
-    };
-
-    Ok(isas)
-}
-
-pub fn all_isas() -> Result<Vec<isa::Isa>, String> {
-    isas_from_targets(vec![])
+pub fn isa_from_arch(arch: &str) -> Result<isa::Isa, String> {
+    isa::Isa::from_arch(arch).ok_or_else(|| format!("no supported isa found for arch `{}`", arch))
 }
 
 /// Generates all the Rust source files used in Cranelift from the meta-language.

cranelift/codegen/src/isa/mod.rs

@@ -68,16 +68,16 @@ use failure_derive::Fail;
 use std::boxed::Box;
 use target_lexicon::{Architecture, PointerWidth, Triple};
 
-#[cfg(build_riscv)]
+#[cfg(feature = "riscv")]
 mod riscv;
 
-#[cfg(build_x86)]
+#[cfg(feature = "x86")]
 mod x86;
 
-#[cfg(build_arm32)]
+#[cfg(feature = "arm32")]
 mod arm32;
 
-#[cfg(build_arm64)]
+#[cfg(feature = "arm64")]
 mod arm64;
 
 mod call_conv;
@@ -90,12 +90,12 @@ mod stack;
 /// Returns a builder that can create a corresponding `TargetIsa`
 /// or `Err(LookupError::Unsupported)` if not enabled.
 macro_rules! isa_builder {
-    ($module:ident, $name:ident) => {{
-        #[cfg($name)]
+    ($name:ident, $feature:tt) => {{
+        #[cfg(feature = $feature)]
         fn $name(triple: Triple) -> Result<Builder, LookupError> {
-            Ok($module::isa_builder(triple))
+            Ok($name::isa_builder(triple))
         };
-        #[cfg(not($name))]
+        #[cfg(not(feature = $feature))]
         fn $name(_triple: Triple) -> Result<Builder, LookupError> {
             Err(LookupError::Unsupported)
         }
@@ -107,9 +107,9 @@ macro_rules! isa_builder {
 /// Return a builder that can create a corresponding `TargetIsa`.
 pub fn lookup(triple: Triple) -> Result<Builder, LookupError> {
     match triple.architecture {
-        Architecture::Riscv32 | Architecture::Riscv64 => isa_builder!(riscv, build_riscv)(triple),
+        Architecture::Riscv32 | Architecture::Riscv64 => isa_builder!(riscv, "riscv")(triple),
         Architecture::I386 | Architecture::I586 | Architecture::I686 | Architecture::X86_64 => {
-            isa_builder!(x86, build_x86)(triple)
+            isa_builder!(x86, "x86")(triple)
         }
         Architecture::Thumbv6m
         | Architecture::Thumbv7em
@@ -118,8 +118,8 @@ pub fn lookup(triple: Triple) -> Result<Builder, LookupError> {
         | Architecture::Armv4t
         | Architecture::Armv5te
         | Architecture::Armv7
-        | Architecture::Armv7s => isa_builder!(arm32, build_arm32)(triple),
-        Architecture::Aarch64 => isa_builder!(arm64, build_arm64)(triple),
+        | Architecture::Armv7s => isa_builder!(arm32, "arm32")(triple),
+        Architecture::Aarch64 => isa_builder!(arm64, "arm64")(triple),
         _ => Err(LookupError::Unsupported),
     }
 }

cranelift/codegen/src/regalloc/pressure.rs

@@ -270,7 +270,7 @@ impl fmt::Display for Pressure {
 }
 
 #[cfg(test)]
-#[cfg(build_arm32)]
+#[cfg(feature = "arm32")]
 mod tests {
     use super::Pressure;
     use crate::isa::{RegClass, TargetIsa};

cranelift/codegen/src/regalloc/solver.rs

@@ -1127,7 +1127,7 @@ impl fmt::Display for Solver {
 }
 
 #[cfg(test)]
-#[cfg(build_arm32)]
+#[cfg(feature = "arm32")]
 mod tests {
     use super::{Move, Solver};
     use crate::entity::EntityRef;