Rollup merge of #114296 - RalfJung:interpret-repeat-align, r=oli-obk

interpret: fix alignment handling for Repeat expressions

Author: matthiaskrgr

tests/pass/align_repeat_into_packed_field.rs

@@ -0,0 +1,22 @@
+#![feature(custom_mir, core_intrinsics)]
+use std::intrinsics::mir::*;
+
+#[repr(packed)]
+struct S { field: [u32; 2] }
+
+#[custom_mir(dialect = "runtime", phase = "optimized")]
+fn test() { mir! {
+    let s: S;
+    {
+        // Store a repeat expression directly into a field of a packed struct.
+        s.field = [0; 2];
+        Return()
+    }
+} }
+
+fn main() {
+    // Run this a bunch of time to make sure it doesn't pass by chance.
+    for _ in 0..20 {
+        test();
+    }
+}

tests/pass/issues/issue-miri-1925.rs renamed to tests/pass/align_repeat_into_well_aligned_array.rs

@@ -4,6 +4,8 @@ use std::mem::size_of;
 
 fn main() {
     let mut a = Params::new();
+    // The array itself here happens to be quite well-aligned, but not all its elements have that
+    // large alignment and we better make sure that is still accepted by Miri.
     a.key_block = [0; BLOCKBYTES];
 }