Fix ICE when using zero-length SIMD type in extern static

Previously, using a zero-length SIMD type in an extern static would
cause an internal compiler error. Now it properly emits a diagnostic
error instead of panicking.

Author: enthropy7

compiler/rustc_hir_analysis/src/check/check.rs

@@ -24,6 +24,7 @@ use rustc_middle::ty::{
     TypeVisitable, TypeVisitableExt, fold_regions,
 };
 use rustc_session::lint::builtin::UNINHABITED_STATIC;
+use rustc_span::source_map::Spanned;
 use rustc_target::spec::{AbiMap, AbiMapping};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::error_reporting::traits::on_unimplemented::OnUnimplementedDirective;
@@ -192,6 +193,12 @@ fn check_static_inhabited(tcx: TyCtxt<'_>, def_id: LocalDefId) {
             tcx.dcx().emit_err(errors::TooLargeStatic { span });
             return;
         }
+        // SIMD types with invalid layout (e.g., zero-length) should emit an error
+        Err(e @ LayoutError::InvalidSimd { .. }) => {
+            let ty_span = tcx.ty_span(def_id);
+            tcx.dcx().emit_err(Spanned { span: ty_span, node: e.into_diagnostic() });
+            return;
+        }
         // Generic statics are rejected, but we still reach this case.
         Err(e) => {
             tcx.dcx().span_delayed_bug(span, format!("{e:?}"));

tests/ui/simd/extern-static-zero-length.rs

@@ -0,0 +1,13 @@
+#![feature(repr_simd)]
+
+#[repr(simd)]
+struct Simd<T, const N: usize>([T; N]);
+
+unsafe extern "C" {
+    static VAR: Simd<u8, 0>;
+    //~^ ERROR the SIMD type `Simd<u8, 0>` has zero elements
+    static VAR2: Simd<u8, 1_000_000>;
+    //~^ ERROR the SIMD type `Simd<u8, 1000000>` has more elements than the limit 32768
+}
+
+fn main() {}

tests/ui/simd/extern-static-zero-length.stderr

@@ -0,0 +1,14 @@
+error: the SIMD type `Simd<u8, 0>` has zero elements
+  --> $DIR/extern-static-zero-length.rs:7:17
+   |
+LL |     static VAR: Simd<u8, 0>;
+   |                 ^^^^^^^^^^^
+
+error: the SIMD type `Simd<u8, 1000000>` has more elements than the limit 32768
+  --> $DIR/extern-static-zero-length.rs:9:18
+   |
+LL |     static VAR2: Simd<u8, 1_000_000>;
+   |                  ^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+