From 41ce1ed252f194756fb2f3e3e92bbdfb3940088d Mon Sep 17 00:00:00 2001
From: Scott McMurray <scottmcm@users.noreply.github.com>
Date: Thu, 6 Mar 2025 19:13:46 -0800
Subject: Ban projecting into SIMD types [MCP838]

---
 compiler/rustc_mir_transform/src/validate.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'compiler/rustc_mir_transform/src')

diff --git a/compiler/rustc_mir_transform/src/validate.rs b/compiler/rustc_mir_transform/src/validate.rs
index 659ca4df159..5860072d541 100644
--- a/compiler/rustc_mir_transform/src/validate.rs
+++ b/compiler/rustc_mir_transform/src/validate.rs
@@ -721,6 +721,15 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                             );
                         }
 
+                        if adt_def.repr().simd() {
+                            self.fail(
+                                location,
+                                format!(
+                                    "Projecting into SIMD type {adt_def:?} is banned by MCP#838"
+                                ),
+                            );
+                        }
+
                         let var = parent_ty.variant_index.unwrap_or(FIRST_VARIANT);
                         let Some(field) = adt_def.variant(var).fields.get(f) else {
                             fail_out_of_bounds(self, location);
-- 
cgit 1.4.1-3-g733a5