Implement the instruction_set attribute

compiler/rustc_middle/src/middle/codegen_fn_attrs.rs

@@ -1,5 +1,5 @@
 use crate::mir::mono::Linkage;
-use rustc_attr::{InlineAttr, OptimizeAttr};
+use rustc_attr::{InlineAttr, InstructionSetAttr, OptimizeAttr};
 use rustc_session::config::SanitizerSet;
 use rustc_span::symbol::Symbol;
 
@@ -34,6 +34,10 @@ pub struct CodegenFnAttrs {
     /// The `#[no_sanitize(...)]` attribute. Indicates sanitizers for which
     /// instrumentation should be disabled inside the annotated function.
     pub no_sanitize: SanitizerSet,
+    /// The `#[instruction_set(set)]` attribute. Indicates if the generated code should
+    /// be generated against a specific instruction set. Only usable on architectures which allow
+    /// switching between multiple instruction sets.
+    pub instruction_set: Option<InstructionSetAttr>,
 }
 
 bitflags! {
@@ -98,6 +102,7 @@ impl CodegenFnAttrs {
             linkage: None,
             link_section: None,
             no_sanitize: SanitizerSet::empty(),
+            instruction_set: None,
         }
     }