Unrolled build for #151628

Rollup merge of #151628 - enthropy7:fix-simd-const-eval-ice, r=RalfJung

Fix ICE in const eval of packed SIMD types with non-power-of-two element counts

fixes #151537

const evaluation of packed SIMD types with non-power-of-two element counts (like `Simd<_, 3>`) was hitting an ICE. the issue was in `check_simd_ptr_alignment` - it asserted that `backend_repr` must be `BackendRepr::SimdVector`, but for packed SIMD types with non-power-of-two counts the compiler uses `BackendRepr::Memory` instead (as mentioned in `rustc_abi/src/layout.rs:1511`).

was fixed by making `check_simd_ptr_alignment` accept both `BackendRepr::SimdVector` and `BackendRepr::Memory` for SIMD types. added a check to ensure we're dealing with a SIMD type, and the alignment logic works the same for both representations.

also i added a test that reproduces the original ICE.

Author: rust-timer

compiler/rustc_const_eval/src/interpret/intrinsics/simd.rs

@@ -2,7 +2,6 @@ use either::Either;
 use rustc_abi::{BackendRepr, Endian};
 use rustc_apfloat::ieee::{Double, Half, Quad, Single};
 use rustc_apfloat::{Float, Round};
-use rustc_data_structures::assert_matches;
 use rustc_middle::mir::interpret::{InterpErrorKind, Pointer, UndefinedBehaviorInfo};
 use rustc_middle::ty::{FloatTy, ScalarInt, SimdAlign};
 use rustc_middle::{bug, err_ub_format, mir, span_bug, throw_unsup_format, ty};
@@ -838,7 +837,20 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         vector_layout: TyAndLayout<'tcx>,
         alignment: SimdAlign,
     ) -> InterpResult<'tcx> {
-        assert_matches!(vector_layout.backend_repr, BackendRepr::SimdVector { .. });
+        // Packed SIMD types with non-power-of-two element counts use BackendRepr::Memory
+        // instead of BackendRepr::SimdVector. We need to handle both cases.
+        // FIXME: remove the BackendRepr::Memory case when SIMD vectors are always passed as BackendRepr::SimdVector.
+        assert!(vector_layout.ty.is_simd(), "check_simd_ptr_alignment called on non-SIMD type");
+        match vector_layout.backend_repr {
+            BackendRepr::SimdVector { .. } | BackendRepr::Memory { .. } => {}
+            _ => {
+                span_bug!(
+                    self.cur_span(),
+                    "SIMD type has unexpected backend_repr: {:?}",
+                    vector_layout.backend_repr
+                );
+            }
+        }
 
         let align = match alignment {
             ty::SimdAlign::Unaligned => {

tests/ui/consts/const-eval/simd/simd-packed-non-pow2.rs

@@ -0,0 +1,18 @@
+//@ check-pass
+// Fixes #151537
+#![feature(portable_simd, core_intrinsics)]
+use std::intrinsics::simd::SimdAlign;
+use std::{ptr::null, simd::prelude::*};
+
+const _: () = {
+    let c = Simd::from_array([0; 3]);
+    unsafe {
+        core::intrinsics::simd::simd_masked_store::<_, _, _, { SimdAlign::Element }>(
+            c,
+            null::<i32>(),
+            c,
+        )
+    };
+};
+
+fn main() {}