add misalignment const-eval test

and some other raw pointer shenanigans while we are at it

Author: RalfJung

tests/ui/consts/const-eval/raw-pointer-ub.rs

@@ -0,0 +1,36 @@
+// normalize-stderr-test "alloc\d+" -> "allocN"
+#![feature(const_pointer_byte_offsets)]
+#![feature(pointer_byte_offsets)]
+#![feature(const_mut_refs)]
+
+const MISALIGNED_LOAD: () = unsafe {
+    let mem = [0u32; 8];
+    let ptr = mem.as_ptr().byte_add(1);
+    let _val = *ptr; //~ERROR: evaluation of constant value failed
+    //~^NOTE: accessing memory with alignment 1, but alignment 4 is required
+};
+
+const MISALIGNED_STORE: () = unsafe {
+    let mut mem = [0u32; 8];
+    let ptr = mem.as_mut_ptr().byte_add(1);
+    *ptr = 0; //~ERROR: evaluation of constant value failed
+    //~^NOTE: accessing memory with alignment 1, but alignment 4 is required
+};
+
+const MISALIGNED_COPY: () = unsafe {
+    let x = &[0_u8; 4];
+    let y = x.as_ptr().cast::<u32>();
+    let mut z = 123;
+    y.copy_to_nonoverlapping(&mut z, 1);
+    //~^NOTE
+    // The actual error points into the implementation of `copy_to_nonoverlapping`.
+};
+
+const OOB: () = unsafe {
+    let mem = [0u32; 1];
+    let ptr = mem.as_ptr().cast::<u64>();
+    let _val = *ptr; //~ERROR: evaluation of constant value failed
+    //~^NOTE: size 4, so pointer to 8 bytes starting at offset 0 is out-of-bounds
+};
+
+fn main() {}

tests/ui/consts/const-eval/raw-pointer-ub.stderr

@@ -0,0 +1,36 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/raw-pointer-ub.rs:9:16
+   |
+LL |     let _val = *ptr;
+   |                ^^^^ accessing memory with alignment 1, but alignment 4 is required
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/raw-pointer-ub.rs:16:5
+   |
+LL |     *ptr = 0;
+   |     ^^^^^^^^ accessing memory with alignment 1, but alignment 4 is required
+
+error[E0080]: evaluation of constant value failed
+  --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
+   |
+   = note: accessing memory with alignment 1, but alignment 4 is required
+   |
+note: inside `copy_nonoverlapping::<u32>`
+  --> $SRC_DIR/core/src/intrinsics.rs:LL:COL
+note: inside `ptr::const_ptr::<impl *const u32>::copy_to_nonoverlapping`
+  --> $SRC_DIR/core/src/ptr/const_ptr.rs:LL:COL
+note: inside `MISALIGNED_COPY`
+  --> $DIR/raw-pointer-ub.rs:24:5
+   |
+LL |     y.copy_to_nonoverlapping(&mut z, 1);
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0080]: evaluation of constant value failed
+  --> $DIR/raw-pointer-ub.rs:32:16
+   |
+LL |     let _val = *ptr;
+   |                ^^^^ dereferencing pointer failed: allocN has size 4, so pointer to 8 bytes starting at offset 0 is out-of-bounds
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0080`.