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Configure which platforms get f16 and f128 enabled by default

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By moving the logic for which platforms get symbols to
`compiler_builtins` rather than rust-lang/rust, we can control where
symbols get enabled without relying on Cargo features. Using Cargo
features turned out to be a problem in [1].

This will help resolve errors like [2].

[1]: https://github.com/rust-lang/rust/issues/128358
[2]: https://github.com/rust-lang/rust/issues/128401
This commit is contained in:
Trevor Gross 2024-08-02 13:48:13 -04:00
parent b32758cdc2
commit b168f56dd4
1 changed files with 44 additions and 2 deletions
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46
library/compiler-builtins/build.rs
View file

@ -42,11 +42,12 @@ impl Target {
fn main() {
println!("cargo:rerun-if-changed=build.rs");
configure_check_cfg();
let target = Target::from_env();
let cwd = env::current_dir().unwrap();
configure_check_cfg();
configure_f16_f128(&target);
println!("cargo:compiler-rt={}", cwd.join("compiler-rt").display());
// Activate libm's unstable features to make full use of Nightly.
@ -259,6 +260,47 @@ fn configure_check_cfg() {
println!("cargo::rustc-check-cfg=cfg(assert_no_panic)");
}
/// Configure whether or not `f16` and `f128` support should be enabled.
fn configure_f16_f128(target: &Target) {
// 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. This does not mean that the
// backend does the right thing, or that the platform doesn't have ABI 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_ok, f128_ok) = match target.arch.as_str() {
// `f16` and `f128` both crash <https://github.com/llvm/llvm-project/issues/94434>
"arm64ec" => (false, false),
// `f16` crashes <https://github.com/llvm/llvm-project/issues/50374>
"s390x" => (false, true),
// `f128` crashes <https://github.com/llvm/llvm-project/issues/96432>
"mips64" | "mips64r6" => (true, false),
// `f128` crashes <https://github.com/llvm/llvm-project/issues/101545>
"powerpc64" if &target.os == "aix" => (true, false),
// `f128` crashes <https://github.com/llvm/llvm-project/issues/41838>
"sparc" | "sparcv9" => (true, false),
// Most everything else works as of LLVM 19
_ => (true, 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_ok && !disable_both {
println!("cargo::rustc-cfg=f16_enabled");
}
if f128_ok && !disable_both {
println!("cargo::rustc-cfg=f128_enabled");
}
}
#[cfg(feature = "c")]
mod c {
use std::collections::{BTreeMap, HashSet};