Remove rustc_args_required_const attribute

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -14,7 +14,6 @@ use rustc_middle::ty::cast::{CastTy, IntTy};
 use rustc_middle::ty::layout::HasTyCtxt;
 use rustc_middle::ty::{self, adjustment::PointerCast, Instance, Ty, TyCtxt};
 use rustc_span::source_map::{Span, DUMMY_SP};
-use rustc_span::symbol::sym;
 use rustc_target::abi::{Abi, Int, LayoutOf, Variants};
 
 impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
@@ -187,9 +186,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     mir::CastKind::Pointer(PointerCast::ReifyFnPointer) => {
                         match *operand.layout.ty.kind() {
                             ty::FnDef(def_id, substs) => {
-                                if bx.cx().tcx().has_attr(def_id, sym::rustc_args_required_const) {
-                                    bug!("reifying a fn ptr that requires const arguments");
-                                }
                                 let instance = ty::Instance::resolve_for_fn_ptr(
                                     bx.tcx(),
                                     ty::ParamEnv::reveal_all(),

compiler/rustc_feature/src/builtin_attrs.rs

@@ -469,7 +469,6 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // ==========================================================================
 
     rustc_attr!(rustc_promotable, AssumedUsed, template!(Word), IMPL_DETAIL),
-    rustc_attr!(rustc_args_required_const, AssumedUsed, template!(List: "N"), INTERNAL_UNSTABLE),
     rustc_attr!(rustc_legacy_const_generics, AssumedUsed, template!(List: "N"), INTERNAL_UNSTABLE),
 
     // ==========================================================================

compiler/rustc_mir/src/interpret/cast.rs

@@ -7,7 +7,6 @@ use rustc_middle::mir::CastKind;
 use rustc_middle::ty::adjustment::PointerCast;
 use rustc_middle::ty::layout::{IntegerExt, TyAndLayout};
 use rustc_middle::ty::{self, FloatTy, Ty, TypeAndMut};
-use rustc_span::symbol::sym;
 use rustc_target::abi::{Integer, LayoutOf, Variants};
 
 use super::{
@@ -49,13 +48,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                         // All reifications must be monomorphic, bail out otherwise.
                         ensure_monomorphic_enough(*self.tcx, src.layout.ty)?;
 
-                        if self.tcx.has_attr(def_id, sym::rustc_args_required_const) {
-                            span_bug!(
-                                self.cur_span(),
-                                "reifying a fn ptr that requires const arguments"
-                            );
-                        }
-
                         let instance = ty::Instance::resolve_for_fn_ptr(
                             *self.tcx,
                             self.param_env,

compiler/rustc_mir/src/interpret/intern.rs

@@ -305,7 +305,6 @@ where
     let base_intern_mode = match intern_kind {
         InternKind::Static(mutbl) => InternMode::Static(mutbl),
         // `Constant` includes array lengths.
-        // `Promoted` includes non-`Copy` array initializers and `rustc_args_required_const` arguments.
         InternKind::Constant | InternKind::Promoted => InternMode::Const,
     };
 

compiler/rustc_mir/src/transform/lower_intrinsics.rs

@@ -5,6 +5,7 @@ use rustc_middle::mir::*;
 use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_span::symbol::{sym, Symbol};
+use rustc_span::Span;
 use rustc_target::spec::abi::Abi;
 
 pub struct LowerIntrinsics;
@@ -119,6 +120,9 @@ impl<'tcx> MirPass<'tcx> for LowerIntrinsics {
                             terminator.kind = TerminatorKind::Goto { target };
                         }
                     }
+                    _ if intrinsic_name.as_str().starts_with("simd_shuffle") => {
+                        validate_simd_shuffle(tcx, args, terminator.source_info.span);
+                    }
                     _ => {}
                 }
             }
@@ -132,9 +136,19 @@ fn resolve_rust_intrinsic(
 ) -> Option<(Symbol, SubstsRef<'tcx>)> {
     if let ty::FnDef(def_id, substs) = *func_ty.kind() {
         let fn_sig = func_ty.fn_sig(tcx);
-        if fn_sig.abi() == Abi::RustIntrinsic {
+        if let Abi::RustIntrinsic | Abi::PlatformIntrinsic = fn_sig.abi() {
             return Some((tcx.item_name(def_id), substs));
         }
     }
     None
 }
+
+fn validate_simd_shuffle(tcx: TyCtxt<'tcx>, args: &[Operand<'tcx>], span: Span) {
+    match &args[2] {
+        Operand::Constant(_) => {} // all good
+        _ => {
+            let msg = format!("last argument of `simd_shuffle` is required to be a `const` item");
+            tcx.sess.span_err(span, &msg);
+        }
+    }
+}