Fix ICE for repr simd on non struct

compiler/rustc_hir_typeck/src/inline_asm.rs

@@ -7,7 +7,7 @@ use rustc_middle::bug;
 use rustc_middle::ty::{self, Article, FloatTy, IntTy, Ty, TyCtxt, TypeVisitableExt, UintTy};
 use rustc_session::lint;
 use rustc_span::def_id::LocalDefId;
-use rustc_span::{Span, Symbol, sym};
+use rustc_span::{ErrorGuaranteed, Span, Symbol, sym};
 use rustc_target::asm::{
     InlineAsmReg, InlineAsmRegClass, InlineAsmRegOrRegClass, InlineAsmType, ModifierInfo,
 };
@@ -27,6 +27,7 @@ enum NonAsmTypeReason<'tcx> {
     InvalidElement(DefId, Ty<'tcx>),
     NotSizedPtr(Ty<'tcx>),
     EmptySIMDArray(Ty<'tcx>),
+    Tainted(ErrorGuaranteed),
 }
 
 impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
@@ -93,6 +94,14 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
                 }
             }
             ty::Adt(adt, args) if adt.repr().simd() => {
+                if !adt.is_struct() {
+                    let guar = self.fcx.dcx().span_delayed_bug(
+                        span,
+                        format!("repr(simd) should only be used on structs, got {}", adt.descr()),
+                    );
+                    return Err(NonAsmTypeReason::Tainted(guar));
+                }
+
                 let fields = &adt.non_enum_variant().fields;
                 if fields.is_empty() {
                     return Err(NonAsmTypeReason::EmptySIMDArray(ty));
@@ -234,6 +243,9 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
                         let msg = format!("use of empty SIMD vector `{ty}`");
                         self.fcx.dcx().struct_span_err(expr.span, msg).emit();
                     }
+                    NonAsmTypeReason::Tainted(_error_guard) => {
+                        // An error has already been reported.
+                    }
                 }
                 return None;
             }

tests/ui/asm/invalid-repr-simd-on-enum-148634.rs

@@ -0,0 +1,16 @@
+//@ needs-asm-support
+#![feature(repr_simd)]
+
+use std::arch::asm;
+
+#[repr(simd)]
+//~^ ERROR attribute should be applied to a struct
+//~| ERROR unsupported representation for zero-variant enum
+enum Es {}
+
+fn main() {
+    unsafe {
+        let mut x: Es;
+        asm!("{}", out(reg) x);
+    }
+}

tests/ui/asm/invalid-repr-simd-on-enum-148634.stderr

@@ -0,0 +1,22 @@
+error[E0517]: attribute should be applied to a struct
+  --> $DIR/invalid-repr-simd-on-enum-148634.rs:6:8
+   |
+LL | #[repr(simd)]
+   |        ^^^^
+...
+LL | enum Es {}
+   | ---------- not a struct
+
+error[E0084]: unsupported representation for zero-variant enum
+  --> $DIR/invalid-repr-simd-on-enum-148634.rs:6:8
+   |
+LL | #[repr(simd)]
+   |        ^^^^
+...
+LL | enum Es {}
+   | ------- zero-variant enum
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0084, E0517.
+For more information about an error, try `rustc --explain E0084`.