'fma' is missing in target-feature

[fsasm]

When setting target-feature=+fma and printing the features via --print cfg only avx and sse* are listed as target features. Also queries like #[cfg(target_feature = "fma")] do not detect fma. FMA instructions like x86_mm256_fmadd_ps are only usable when fma is enable via target-feature as expected.

The output of rustc -C target-feature=+fma --print cfg is

debug_assertions
target_arch="x86_64"
target_endian="little"
target_env="gnu"
target_family="unix"
target_feature="avx"
target_feature="sse"
target_feature="sse2"
target_feature="sse3"
target_feature="sse4.1"
target_feature="sse4.2"
target_feature="ssse3"
target_has_atomic="16"
target_has_atomic="32"
target_has_atomic="64"
target_has_atomic="8"
target_has_atomic="ptr"
target_os="linux"
target_pointer_width="64"
target_thread_local
target_vendor="unknown"
unix

and the expected output is

[...]
target_feature="fma"
target_feature="avx"
target_feature="sse"
target_feature="sse2"
target_feature="sse3"
target_feature="sse4.1"
target_feature="sse4.2"
target_feature="ssse3"
[...]

Also this example

#![feature(cfg_target_feature)]

fn main() {
    #[cfg(target_feature = "fma")]
    println!("FMA is supported");

    #[cfg(not(target_feature = "fma"))]
    println!("FMA is not supported");
}

outputs FMA is not supported even if it was enabled.

Meta

rustc --version --verbose:
rustc 1.17.0-nightly (b1e3176 2017-03-03)
binary: rustc
commit-hash: b1e3176
commit-date: 2017-03-03
host: x86_64-unknown-linux-gnu
release: 1.17.0-nightly
LLVM version: 3.9

[nagisa]

Rustc does not expose all the LLVM features via attributes consciously. Not a bug. If you want it added your best bet is to make a PR.

[fsasm]

Wouldn't it be better to output a warning in such a case?