Add f16 and f128 configuration from compiler-builtins

In preparation of adding routines from these two types, duplicate the
`compiler-builtins` configuration here.

Author: tgross35

Cargo.toml

@@ -21,14 +21,17 @@ arch = []
 
 # This tells the compiler to assume that a Nightly toolchain is being used and
 # that it should activate any useful Nightly things accordingly.
-unstable = ["unstable-intrinsics"]
+unstable = ["unstable-intrinsics", "unstable-float"]
 
 # Enable calls to functions in `core::intrinsics`
 unstable-intrinsics = []
 
 # Make some internal things public for testing.
 unstable-test-support = []
 
+# Enable the nightly-only `f16` and `f128`.
+unstable-float = []
+
 # Used to prevent using any intrinsics or arch-specific code.
 #
 # HACK: this is a negative feature which is generally a bad idea in Cargo, but

build.rs

@@ -1,6 +1,10 @@
 use std::env;
 
+mod configure;
+
 fn main() {
+    let cfg = configure::Config::from_env();
+
     println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rustc-check-cfg=cfg(assert_no_panic)");
 
@@ -14,29 +18,5 @@ fn main() {
         }
     }
 
-    configure_intrinsics();
-    configure_arch();
-}
-
-/// Simplify the feature logic for enabling intrinsics so code only needs to use
-/// `cfg(intrinsics_enabled)`.
-fn configure_intrinsics() {
-    println!("cargo:rustc-check-cfg=cfg(intrinsics_enabled)");
-
-    // Disabled by default; `unstable-intrinsics` enables again; `force-soft-floats` overrides
-    // to disable.
-    if cfg!(feature = "unstable-intrinsics") && !cfg!(feature = "force-soft-floats") {
-        println!("cargo:rustc-cfg=intrinsics_enabled");
-    }
-}
-
-/// Simplify the feature logic for enabling arch-specific features so code only needs to use
-/// `cfg(arch_enabled)`.
-fn configure_arch() {
-    println!("cargo:rustc-check-cfg=cfg(arch_enabled)");
-
-    // Enabled by default via the "arch" feature, `force-soft-floats` overrides to disable.
-    if cfg!(feature = "arch") && !cfg!(feature = "force-soft-floats") {
-        println!("cargo:rustc-cfg=arch_enabled");
-    }
+    configure::emit_libm_config(&cfg);
 }

configure.rs

@@ -0,0 +1,168 @@
+// Configuration shared with both libm and libm-test
+
+use std::env;
+use std::path::PathBuf;
+
+#[allow(dead_code)]
+pub struct Config {
+    pub manifest_dir: PathBuf,
+    pub out_dir: PathBuf,
+    pub opt_level: u8,
+    pub target_arch: String,
+    pub target_env: String,
+    pub target_family: Option<String>,
+    pub target_os: String,
+    pub target_string: String,
+    pub target_vendor: String,
+    pub target_features: Vec<String>,
+}
+
+impl Config {
+    pub fn from_env() -> Self {
+        let target_features = env::var("CARGO_CFG_TARGET_FEATURE")
+            .map(|feats| feats.split(',').map(ToOwned::to_owned).collect())
+            .unwrap_or_default();
+
+        Self {
+            manifest_dir: PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap()),
+            out_dir: PathBuf::from(env::var("OUT_DIR").unwrap()),
+            opt_level: env::var("OPT_LEVEL").unwrap().parse().unwrap(),
+            target_arch: env::var("CARGO_CFG_TARGET_ARCH").unwrap(),
+            target_env: env::var("CARGO_CFG_TARGET_ENV").unwrap(),
+            target_family: env::var("CARGO_CFG_TARGET_FAMILY").ok(),
+            target_os: env::var("CARGO_CFG_TARGET_OS").unwrap(),
+            target_string: env::var("TARGET").unwrap(),
+            target_vendor: env::var("CARGO_CFG_TARGET_VENDOR").unwrap(),
+            target_features,
+        }
+    }
+}
+
+/// Libm gets most config options made available.
+#[allow(dead_code)]
+pub fn emit_libm_config(cfg: &Config) {
+    emit_intrinsics_cfg();
+    emit_arch_cfg();
+    emit_optimization_cfg(cfg);
+    emit_cfg_shorthands(cfg);
+    emit_f16_f128_cfg(cfg);
+}
+
+/// Tests don't need most feature-related config.
+#[allow(dead_code)]
+pub fn emit_test_config(cfg: &Config) {
+    emit_optimization_cfg(cfg);
+    emit_cfg_shorthands(cfg);
+    emit_f16_f128_cfg(cfg);
+}
+
+/// Simplify the feature logic for enabling intrinsics so code only needs to use
+/// `cfg(intrinsics_enabled)`.
+fn emit_intrinsics_cfg() {
+    println!("cargo:rustc-check-cfg=cfg(intrinsics_enabled)");
+
+    // Disabled by default; `unstable-intrinsics` enables again; `force-soft-floats` overrides
+    // to disable.
+    if cfg!(feature = "unstable-intrinsics") && !cfg!(feature = "force-soft-floats") {
+        println!("cargo:rustc-cfg=intrinsics_enabled");
+    }
+}
+
+/// Simplify the feature logic for enabling arch-specific features so code only needs to use
+/// `cfg(arch_enabled)`.
+fn emit_arch_cfg() {
+    println!("cargo:rustc-check-cfg=cfg(arch_enabled)");
+
+    // Enabled by default via the "arch" feature, `force-soft-floats` overrides to disable.
+    if cfg!(feature = "arch") && !cfg!(feature = "force-soft-floats") {
+        println!("cargo:rustc-cfg=arch_enabled");
+    }
+}
+
+/// Some tests are extremely slow. Emit a config option based on optimization level.
+fn emit_optimization_cfg(cfg: &Config) {
+    println!("cargo:rustc-check-cfg=cfg(optimizations_enabled)");
+
+    if cfg.opt_level >= 2 {
+        println!("cargo:rustc-cfg=optimizations_enabled");
+    }
+}
+
+/// Provide an alias for common longer config combinations.
+fn emit_cfg_shorthands(cfg: &Config) {
+    println!("cargo:rustc-check-cfg=cfg(x86_no_sse)");
+    if cfg.target_arch == "x86" && !cfg.target_features.iter().any(|f| f == "sse") {
+        // Shorthand to detect i586 targets
+        println!("cargo:rustc-cfg=x86_no_sse");
+    }
+}
+
+/// Configure whether or not `f16` and `f128` support should be enabled.
+fn emit_f16_f128_cfg(cfg: &Config) {
+    println!("cargo:rustc-check-cfg=cfg(f16_enabled)");
+    println!("cargo:rustc-check-cfg=cfg(f128_enabled)");
+
+    // `unstable-float` enables these features.
+    if !cfg!(feature = "unstable-float") {
+        return;
+    }
+
+    // Set whether or not `f16` and `f128` are supported at a basic level by LLVM. This only means
+    // that the backend will not crash when using these types and generates code that can be called
+    // without crashing (no infinite recursion). This does not mean that the platform doesn't have
+    // ABI or other bugs.
+    //
+    // We do this here rather than in `rust-lang/rust` because configuring via cargo features is
+    // not straightforward.
+    //
+    // Original source of this list:
+    // <https://github.com/rust-lang/compiler-builtins/pull/652#issuecomment-2266151350>
+    let f16_enabled = match cfg.target_arch.as_str() {
+        // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
+        "arm64ec" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/50374>
+        "s390x" => false,
+        // Infinite recursion <https://github.com/llvm/llvm-project/issues/97981>
+        // FIXME(llvm): loongarch fixed by <https://github.com/llvm/llvm-project/pull/107791>
+        "csky" => false,
+        "hexagon" => false,
+        "loongarch64" => false,
+        "mips" | "mips64" | "mips32r6" | "mips64r6" => false,
+        "powerpc" | "powerpc64" => false,
+        "sparc" | "sparc64" => false,
+        "wasm32" | "wasm64" => false,
+        // Most everything else works as of LLVM 19
+        _ => true,
+    };
+
+    let f128_enabled = match cfg.target_arch.as_str() {
+        // Unsupported (libcall is not supported) <https://github.com/llvm/llvm-project/issues/121122>
+        "amdgpu" => false,
+        // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
+        "arm64ec" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/96432>
+        "mips64" | "mips64r6" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/95471>
+        "nvptx64" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/101545>
+        "powerpc64" if &cfg.target_os == "aix" => false,
+        // Selection failure <https://github.com/llvm/llvm-project/issues/41838>
+        "sparc" => false,
+        // Most everything else works as of LLVM 19
+        _ => true,
+    };
+
+    // If the feature is set, disable these types.
+    let disable_both = env::var_os("CARGO_FEATURE_NO_F16_F128").is_some();
+
+    println!("cargo:rustc-check-cfg=cfg(f16_enabled)");
+    println!("cargo:rustc-check-cfg=cfg(f128_enabled)");
+
+    if f16_enabled && !disable_both {
+        println!("cargo:rustc-cfg=f16_enabled");
+    }
+
+    if f128_enabled && !disable_both {
+        println!("cargo:rustc-cfg=f128_enabled");
+    }
+}

crates/compiler-builtins-smoke-test/Cargo.toml

@@ -21,5 +21,7 @@ force-soft-floats = []
 unexpected_cfgs = { level = "warn", check-cfg = [
   "cfg(arch_enabled)",
   "cfg(assert_no_panic)",
+  "cfg(f128_enabled)",
+  "cfg(f16_enabled)",
   "cfg(intrinsics_enabled)",
 ] }

crates/libm-macros/Cargo.toml

@@ -12,3 +12,10 @@ heck = "0.5.0"
 proc-macro2 = "1.0.88"
 quote = "1.0.37"
 syn = { version = "2.0.79", features = ["full", "extra-traits", "visit-mut"] }
+
+[lints.rust]
+# Values used during testing
+unexpected_cfgs = { level = "warn", check-cfg = [
+  'cfg(f16_enabled)',
+  'cfg(f128_enabled)',
+] }

crates/libm-test/Cargo.toml

@@ -5,7 +5,10 @@ edition = "2021"
 publish = false
 
 [features]
-default = []
+default = ["unstable-float"]
+
+# Propagated from libm because this affects which functions we test.
+unstable-float = ["libm/unstable-float"]
 
 # Generate tests which are random inputs and the outputs are calculated with
 # musl libc.
@@ -44,3 +47,9 @@ criterion = { version = "0.5.1", default-features = false, features = ["cargo_be
 [[bench]]
 name = "random"
 harness = false
+
+[lints.rust]
+# Values from the chared config.rs used by `libm` but not the test crate
+unexpected_cfgs = { level = "warn", check-cfg = [
+  'cfg(feature, values("arch", "force-soft-floats", "unstable-intrinsics"))',
+] }

crates/libm-test/build.rs

@@ -1,66 +1,16 @@
 use std::fmt::Write;
-use std::path::PathBuf;
-use std::{env, fs};
+use std::fs;
+
+#[path = "../../configure.rs"]
+mod configure;
+use configure::Config;
 
 fn main() {
     let cfg = Config::from_env();
 
-    emit_optimization_cfg(&cfg);
-    emit_cfg_shorthands(&cfg);
     list_all_tests(&cfg);
-}
-
-#[allow(dead_code)]
-struct Config {
-    manifest_dir: PathBuf,
-    out_dir: PathBuf,
-    opt_level: u8,
-    target_arch: String,
-    target_env: String,
-    target_family: Option<String>,
-    target_os: String,
-    target_string: String,
-    target_vendor: String,
-    target_features: Vec<String>,
-}
-
-impl Config {
-    fn from_env() -> Self {
-        let target_features = env::var("CARGO_CFG_TARGET_FEATURE")
-            .map(|feats| feats.split(',').map(ToOwned::to_owned).collect())
-            .unwrap_or_default();
-
-        Self {
-            manifest_dir: PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap()),
-            out_dir: PathBuf::from(env::var("OUT_DIR").unwrap()),
-            opt_level: env::var("OPT_LEVEL").unwrap().parse().unwrap(),
-            target_arch: env::var("CARGO_CFG_TARGET_ARCH").unwrap(),
-            target_env: env::var("CARGO_CFG_TARGET_ENV").unwrap(),
-            target_family: env::var("CARGO_CFG_TARGET_FAMILY").ok(),
-            target_os: env::var("CARGO_CFG_TARGET_OS").unwrap(),
-            target_string: env::var("TARGET").unwrap(),
-            target_vendor: env::var("CARGO_CFG_TARGET_VENDOR").unwrap(),
-            target_features,
-        }
-    }
-}
 
-/// Some tests are extremely slow. Emit a config option based on optimization level.
-fn emit_optimization_cfg(cfg: &Config) {
-    println!("cargo::rustc-check-cfg=cfg(optimizations_enabled)");
-
-    if cfg.opt_level >= 2 {
-        println!("cargo::rustc-cfg=optimizations_enabled");
-    }
-}
-
-/// Provide an alias for common longer config combinations.
-fn emit_cfg_shorthands(cfg: &Config) {
-    println!("cargo::rustc-check-cfg=cfg(x86_no_sse)");
-    if cfg.target_arch == "x86" && !cfg.target_features.iter().any(|f| f == "sse") {
-        // Shorthand to detect i586 targets
-        println!("cargo::rustc-cfg=x86_no_sse");
-    }
+    configure::emit_test_config(&cfg);
 }
 
 /// Create a list of all source files in an array. This can be used for making sure that

src/lib.rs

@@ -2,6 +2,8 @@
 #![no_std]
 #![cfg_attr(intrinsics_enabled, allow(internal_features))]
 #![cfg_attr(intrinsics_enabled, feature(core_intrinsics))]
+#![cfg_attr(f128_enabled, feature(f128))]
+#![cfg_attr(f16_enabled, feature(f16))]
 #![allow(clippy::assign_op_pattern)]
 #![allow(clippy::deprecated_cfg_attr)]
 #![allow(clippy::eq_op)]

src/math/support/float_traits.rs

@@ -219,5 +219,9 @@ macro_rules! float_impl {
     };
 }
 
+#[cfg(f16_enabled)]
+float_impl!(f16, u16, i16, i8, 16, 10);
 float_impl!(f32, u32, i32, i16, 32, 23);
 float_impl!(f64, u64, i64, i16, 64, 52);
+#[cfg(f128_enabled)]
+float_impl!(f128, u128, i128, i16, 128, 112);