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

4 files changed, 30 insertions, 23 deletions

diff --git a/compiler/rustc_codegen_cranelift/example/float-minmax-pass.rs b/compiler/rustc_codegen_cranelift/example/float-minmax-pass.rs
index ad46e18c11c..b7491b7e522 100644
--- a/compiler/rustc_codegen_cranelift/example/float-minmax-pass.rs
+++ b/compiler/rustc_codegen_cranelift/example/float-minmax-pass.rs
@@ -11,6 +11,12 @@
 #[derive(Copy, Clone, PartialEq, Debug)]
 struct f32x4(pub [f32; 4]);
 
+impl f32x4 {
+    fn into_array(self) -> [f32; 4] {
+        unsafe { std::mem::transmute(self) }
+    }
+}
+
 use std::intrinsics::simd::*;
 
 fn main() {
@@ -29,22 +35,22 @@ fn main() {
     unsafe {
         let min0 = simd_fmin(x, y);
         let min1 = simd_fmin(y, x);
-        assert_eq!(min0, min1);
+        assert_eq!(min0.into_array(), min1.into_array());
         let e = f32x4([1.0, 1.0, 3.0, 3.0]);
-        assert_eq!(min0, e);
+        assert_eq!(min0.into_array(), e.into_array());
         let minn = simd_fmin(x, n);
-        assert_eq!(minn, x);
+        assert_eq!(minn.into_array(), x.into_array());
         let minn = simd_fmin(y, n);
-        assert_eq!(minn, y);
+        assert_eq!(minn.into_array(), y.into_array());
 
         let max0 = simd_fmax(x, y);
         let max1 = simd_fmax(y, x);
-        assert_eq!(max0, max1);
+        assert_eq!(max0.into_array(), max1.into_array());
         let e = f32x4([2.0, 2.0, 4.0, 4.0]);
-        assert_eq!(max0, e);
+        assert_eq!(max0.into_array(), e.into_array());
         let maxn = simd_fmax(x, n);
-        assert_eq!(maxn, x);
+        assert_eq!(maxn.into_array(), x.into_array());
         let maxn = simd_fmax(y, n);
-        assert_eq!(maxn, y);
+        assert_eq!(maxn.into_array(), y.into_array());
     }
 }
diff --git a/compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs b/compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs
index 246bd3104ec..86602c6b2a3 100644
--- a/compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs
+++ b/compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs
@@ -348,7 +348,8 @@ fn main() {
     struct V([f64; 2]);
 
     let f = V([0.0, 1.0]);
-    let _a = f.0[0];
+    let fp = (&raw const f) as *const [f64; 2];
+    let _a = (unsafe { &*fp })[0];
 
     stack_val_align();
 }
diff --git a/compiler/rustc_codegen_ssa/src/mir/operand.rs b/compiler/rustc_codegen_ssa/src/mir/operand.rs
index 6a3fdb6ede1..06bedaaa4a2 100644
--- a/compiler/rustc_codegen_ssa/src/mir/operand.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/operand.rs
@@ -329,20 +329,11 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
         let offset = self.layout.fields.offset(i);
 
         if !bx.is_backend_ref(self.layout) && bx.is_backend_ref(field) {
-            if let BackendRepr::SimdVector { count, .. } = self.layout.backend_repr
-                && let BackendRepr::Memory { sized: true } = field.backend_repr
-                && count.is_power_of_two()
-            {
-                assert_eq!(field.size, self.layout.size);
-                // This is being deprecated, but for now stdarch still needs it for
-                // Newtype vector of array, e.g. #[repr(simd)] struct S([i32; 4]);
-                let place = PlaceRef::alloca(bx, field);
-                self.val.store(bx, place.val.with_type(self.layout));
-                return bx.load_operand(place);
-            } else {
-                // Part of https://github.com/rust-lang/compiler-team/issues/838
-                bug!("Non-ref type {self:?} cannot project to ref field type {field:?}");
-            }
+            // Part of https://github.com/rust-lang/compiler-team/issues/838
+            span_bug!(
+                fx.mir.span,
+                "Non-ref type {self:?} cannot project to ref field type {field:?}",
+            );
         }
 
         let val = if field.is_zst() {
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);