Auto merge of rust-lang#69509 - RalfJung:debug-assert-write, r=eddyb

debug-assert ptr sanity in ptr::write

This is a re-submission of the parts that we removed from rust-lang#69208 due to ["interesting" test failures](rust-lang#69208 (comment)).

Fixes rust-lang#53871
r? @Mark-Simulacrum @eddyb

src/libcore/ptr/mod.rs

@@ -810,9 +810,7 @@ pub unsafe fn read_unaligned<T>(src: *const T) -> T {
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub unsafe fn write<T>(dst: *mut T, src: T) {
-    // FIXME: the debug assertion here causes codegen test failures on some architectures.
-    // See <https://github.com/rust-lang/rust/pull/69208#issuecomment-591326757>.
-    // debug_assert!(is_aligned_and_not_null(dst), "attempt to write to unaligned or null pointer");
+    debug_assert!(is_aligned_and_not_null(dst), "attempt to write to unaligned or null pointer");
     intrinsics::move_val_init(&mut *dst, src)
 }
 

src/test/codegen/repeat-trusted-len.rs

@@ -5,14 +5,9 @@
 
 use std::iter;
 
-// CHECK: @helper([[USIZE:i[0-9]+]] %_1)
-#[no_mangle]
-pub fn helper(_: usize) {
-}
-
 // CHECK-LABEL: @repeat_take_collect
 #[no_mangle]
 pub fn repeat_take_collect() -> Vec<u8> {
-// CHECK: call void @llvm.memset.p0i8.[[USIZE]](i8* {{(nonnull )?}}align 1{{.*}} %{{[0-9]+}}, i8 42, [[USIZE]] 100000, i1 false)
+// CHECK: call void @llvm.memset.p0i8.i{{[0-9]+}}(i8* {{(nonnull )?}}align 1{{.*}} %{{[0-9]+}}, i8 42, i{{[0-9]+}} 100000, i1 false)
     iter::repeat(42).take(100000).collect()
 }

src/test/ui/issues/issue-40883.rs

@@ -71,15 +71,16 @@ pub fn supersize_me(out: &mut Vec<Big>) {
 
 #[inline(never)]
 fn verify_stack_usage(before_ptr: *mut Vec<Big>) {
-    // to check stack usage, create locals before and after
+    // To check stack usage, create locals before and after
     // and check the difference in addresses between them.
     let mut stack_var: Vec<Big> = vec![];
     test::black_box(&mut stack_var);
     let stack_usage = isize::abs(
         (&mut stack_var as *mut _ as isize) -
             (before_ptr as isize)) as usize;
-    // give space for 2 copies of `Big` + 128 "misc" bytes.
-    if stack_usage > mem::size_of::<Big>() * 2 + 128 {
+    // Give space for 2 copies of `Big` + 272 "misc" bytes
+    // (value observed on x86_64-pc-windows-gnu).
+    if stack_usage > mem::size_of::<Big>() * 2 + 272 {
         panic!("used {} bytes of stack, but `struct Big` is only {} bytes",
                stack_usage, mem::size_of::<Big>());
     }