Rollup merge of rust-lang#155235 - folkertdev:fma4-target-feature, r=sayantn

add the `fma4` x86 target feature

tracking issue: rust-lang#155233

Implications are based on LLVM

https://github.com/llvm/llvm-project/blob/df6c82053c5e1f9814d130d423f34871bc6423c5/llvm/lib/Target/X86/X86.td#L201-L206

This feature adds a slightly better instruction encoding for fma. We might want to expose the intrinsics in `stdarch` with that target feature, but just adding the target feature in user code should already take advantage of this improved encoding.

This target feature is used in `libm`.

r? sayantn

Author: JonathanBrouwer

compiler/rustc_feature/src/unstable.rs

@@ -512,6 +512,8 @@ declare_features! (
     (incomplete, field_projections, "CURRENT_RUSTC_VERSION", Some(145383)),
     /// Allows marking trait functions as `final` to prevent overriding impls
     (unstable, final_associated_functions, "1.95.0", Some(131179)),
+    /// fma4 target feature on x86.
+    (unstable, fma4_target_feature, "CURRENT_RUSTC_VERSION", Some(155233)),
     /// Controlling the behavior of fmt::Debug
     (unstable, fmt_debug, "1.82.0", Some(129709)),
     /// Allows using `#[align(...)]` on function items

compiler/rustc_span/src/symbol.rs

@@ -952,6 +952,7 @@ symbols! {
         floorf32,
         floorf64,
         floorf128,
+        fma4_target_feature,
         fmaf16,
         fmaf32,
         fmaf64,

compiler/rustc_target/src/target_features.rs

@@ -422,6 +422,7 @@ static X86_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("ermsb", Unstable(sym::ermsb_target_feature), &[]),
     ("f16c", Stable, &["avx"]),
     ("fma", Stable, &["avx"]),
+    ("fma4", Unstable(sym::fma4_target_feature), &["avx", "sse4a"]),
     ("fxsr", Stable, &[]),
     ("gfni", Stable, &["sse2"]),
     ("kl", Stable, &["sse2"]),
@@ -467,7 +468,7 @@ static X86_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("vpclmulqdq", Stable, &["avx", "pclmulqdq"]),
     ("widekl", Stable, &["kl"]),
     ("x87", Unstable(sym::x87_target_feature), &[]),
-    ("xop", Unstable(sym::xop_target_feature), &[/*"fma4", */ "avx", "sse4a"]),
+    ("xop", Unstable(sym::xop_target_feature), &["fma4", "avx", "sse4a"]),
     ("xsave", Stable, &[]),
     ("xsavec", Stable, &["xsave"]),
     ("xsaveopt", Stable, &["xsave"]),

tests/ui/check-cfg/target_feature.stderr

@@ -111,6 +111,7 @@ LL |     cfg!(target_feature = "_UNEXPECTED_VALUE");
 `float7e60`
 `floate1`
 `fma`
+`fma4`
 `fp-armv8`
 `fp16`
 `fp64`

tests/ui/feature-gates/feature-gate-fma4_target_feature.rs

@@ -0,0 +1,6 @@
+//@ only-x86_64
+#[target_feature(enable = "fma4")]
+//~^ ERROR: currently unstable
+unsafe fn foo() {}
+
+fn main() {}

tests/ui/feature-gates/feature-gate-fma4_target_feature.stderr

@@ -0,0 +1,13 @@
+error[E0658]: the target feature `fma4` is currently unstable
+  --> $DIR/feature-gate-fma4_target_feature.rs:2:18
+   |
+LL | #[target_feature(enable = "fma4")]
+   |                  ^^^^^^^^^^^^^^^
+   |
+   = note: see issue #155233 <https://github.com/rust-lang/rust/issues/155233> for more information
+   = help: add `#![feature(fma4_target_feature)]` to the crate attributes to enable
+   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0658`.

tests/ui/target-feature/invalid-attribute.stderr

@@ -161,7 +161,7 @@ error: the feature named `foo` is not valid for this target
 LL | #[target_feature(enable = "foo")]
    |                  ^^^^^^^^^^^^^^ `foo` is not valid for this target
    |
-   = help: valid names are: `fma`, `xop`, `adx`, `aes`, and `avx` and 74 more
+   = help: valid names are: `fma`, `xop`, `adx`, `aes`, and `avx` and 75 more
 
 error[E0046]: not all trait items implemented, missing: `foo`
   --> $DIR/invalid-attribute.rs:81:1
@@ -213,15 +213,15 @@ error: the feature named `sse5` is not valid for this target
 LL | #[target_feature(enable = "sse5")]
    |                  ^^^^^^^^^^^^^^^ `sse5` is not valid for this target
    |
-   = help: valid names are: `sse`, `sse2`, `sse3`, `sse4a`, and `ssse3` and 74 more
+   = help: valid names are: `sse`, `sse2`, `sse3`, `sse4a`, and `ssse3` and 75 more
 
 error: the feature named `avx512` is not valid for this target
   --> $DIR/invalid-attribute.rs:127:18
    |
 LL | #[target_feature(enable = "avx512")]
    |                  ^^^^^^^^^^^^^^^^^ `avx512` is not valid for this target
    |
-   = help: valid names are: `avx512f`, `avx2`, `avx512bw`, `avx512cd`, and `avx512dq` and 74 more
+   = help: valid names are: `avx512f`, `avx2`, `avx512bw`, `avx512cd`, and `avx512dq` and 75 more
 
 error: aborting due to 26 previous errors