Auto merge of #143833 - scottmcm:final-mcp-838, r=compiler-errors

Ban projecting into SIMD types [MCP838]

Closes https://github.com/rust-lang/compiler-team/issues/838

The actual compiler change here is tiny; there's just a bazillion tests to update.

~~Since I'm sure I've missed some, for now~~
~~r ghost~~

try-job: test-various
try-job: x86_64-gnu-nopt

1 files changed, 9 insertions, 0 deletions

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);