Auto merge of #127537 - veluca93:struct_tf, r=BoxyUwU

Implement a first version of RFC 3525: struct target features

This PR is an attempt at implementing https://github.com/rust-lang/rfcs/pull/3525, behind a feature gate `struct_target_features`.

There's obviously a few tasks that ought to be done before this is merged; in no particular order:
- add proper error messages
- add tests
- create a tracking issue for the RFC
- properly serialize/deserialize the new target_features field in `rmeta` (assuming I even understood that correctly :-))

That said, as I am definitely not a `rustc` expert, I'd like to get some early feedback on the overall approach before fixing those things (and perhaps some pointers for `rmeta`...), hence this early PR :-)

Here's an example piece of code that I have been using for testing - with the new code, the calls to intrinsics get correctly inlined:
```rust
#![feature(struct_target_features)]

use std::arch::x86_64::*;

/*
// fails to compile
#[target_feature(enable = "avx")]
struct Invalid(u32);
*/

#[target_feature(enable = "avx")]
struct Avx {}

#[target_feature(enable = "sse")]
struct Sse();

/*
// fails to compile
extern "C" fn bad_fun(_: Avx) {}
*/

/*
// fails to compile
#[inline(always)]
fn inline_fun(_: Avx) {}
*/

trait Simd {
    fn do_something(&self);
}

impl Simd for Avx {
    fn do_something(&self) {
        unsafe {
            println!("{:?}", _mm256_setzero_ps());
        }
    }
}

impl Simd for Sse {
    fn do_something(&self) {
        unsafe {
            println!("{:?}", _mm_setzero_ps());
        }
    }
}

struct WithAvx {
    #[allow(dead_code)]
    avx: Avx,
}

impl Simd for WithAvx {
    fn do_something(&self) {
        unsafe {
            println!("{:?}", _mm256_setzero_ps());
        }
    }
}

#[inline(never)]
fn dosomething<S: Simd>(simd: &S) {
    simd.do_something();
}

fn main() {
    /*
    // fails to compile
    Avx {};
    */

    if is_x86_feature_detected!("avx") {
        let avx = unsafe { Avx {} };
        dosomething(&avx);
        dosomething(&WithAvx { avx });
    }
    if is_x86_feature_detected!("sse") {
        dosomething(&unsafe { Sse {} })
    }
}
```

Tracking:

- https://github.com/rust-lang/rust/issues/129107

1 files changed, 6 insertions, 1 deletions

diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index c785b235f61..6434bd0d7bf 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -47,7 +47,7 @@ use {rustc_ast as ast, rustc_attr as attr, rustc_hir as hir};
 use crate::infer::canonical::{self, Canonical};
 use crate::lint::LintExpectation;
 use crate::metadata::ModChild;
-use crate::middle::codegen_fn_attrs::CodegenFnAttrs;
+use crate::middle::codegen_fn_attrs::{CodegenFnAttrs, TargetFeature};
 use crate::middle::debugger_visualizer::DebuggerVisualizerFile;
 use crate::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo};
 use crate::middle::lib_features::LibFeatures;
@@ -1245,6 +1245,11 @@ rustc_queries! {
         feedable
     }
 
+    query struct_target_features(def_id: DefId) -> &'tcx [TargetFeature] {
+        separate_provide_extern
+        desc { |tcx| "computing target features for struct `{}`", tcx.def_path_str(def_id) }
+    }
+
     query asm_target_features(def_id: DefId) -> &'tcx FxIndexSet<Symbol> {
         desc { |tcx| "computing target features for inline asm of `{}`", tcx.def_path_str(def_id) }
     }