Forbid the use of #[target_feature] on main

compiler/rustc_hir_analysis/messages.ftl

@@ -128,6 +128,8 @@ hir_analysis_where_clause_on_main = `main` function is not allowed to have a `wh
 hir_analysis_track_caller_on_main = `main` function is not allowed to be `#[track_caller]`
     .suggestion = remove this annotation
 
+hir_analysis_target_feature_on_main = `main` function is not allowed to have `#[target_feature]`
+
 hir_analysis_start_not_track_caller = `start` is not allowed to be `#[track_caller]`
     .label = `start` is not allowed to be `#[track_caller]`
 

compiler/rustc_hir_analysis/src/errors.rs

@@ -327,6 +327,14 @@ pub(crate) struct TrackCallerOnMain {
     pub annotated: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(hir_analysis_target_feature_on_main)]
+pub(crate) struct TargetFeatureOnMain {
+    #[primary_span]
+    #[label(hir_analysis_target_feature_on_main)]
+    pub main: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(hir_analysis_start_not_track_caller)]
 pub(crate) struct StartTrackCaller {

compiler/rustc_hir_analysis/src/lib.rs

@@ -283,6 +283,11 @@ fn check_main_fn_ty(tcx: TyCtxt<'_>, main_def_id: DefId) {
         error = true;
     }
 
+    if !tcx.codegen_fn_attrs(main_def_id).target_features.is_empty() {
+        tcx.sess.emit_err(errors::TargetFeatureOnMain { main: main_span });
+        error = true;
+    }
+
     if error {
         return;
     }

tests/ui/asm/x86_64/issue-89875.rs

@@ -7,7 +7,7 @@
 use std::arch::asm;
 
 #[target_feature(enable = "avx")]
-fn main() {
+fn foo() {
     unsafe {
         asm!(
             "/* {} */",
@@ -15,3 +15,5 @@ fn main() {
         );
     }
 }
+
+fn main() {}

tests/ui/rfcs/rfc-2396-target_feature-11/issue-108645-target-feature-on-main.rs

@@ -0,0 +1,7 @@
+// only-x86_64
+
+#![feature(target_feature_11)]
+
+#[target_feature(enable = "avx2")]
+fn main() {}
+//~^ ERROR `main` function is not allowed to have `#[target_feature]`

tests/ui/rfcs/rfc-2396-target_feature-11/issue-108645-target-feature-on-main.stderr

@@ -0,0 +1,8 @@
+error: `main` function is not allowed to have `#[target_feature]`
+  --> $DIR/issue-108645-target-feature-on-main.rs:6:1
+   |
+LL | fn main() {}
+   | ^^^^^^^^^ `main` function is not allowed to have `#[target_feature]`
+
+error: aborting due to previous error
+