From bbf175df3cd17763ff601151eed6f84d0cabda13 Mon Sep 17 00:00:00 2001
From: Camelid <camelidcamel@gmail.com>
Date: Mon, 4 Jan 2021 18:34:31 -0800
Subject: [PATCH] Make `size_of_val` and `min_align_of_val` intrinsics unsafe

---
 compiler/rustc_typeck/src/check/intrinsic.rs |  2 --
 library/core/src/mem/mod.rs                  | 16 +++++++++++-----
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/compiler/rustc_typeck/src/check/intrinsic.rs b/compiler/rustc_typeck/src/check/intrinsic.rs
index 673dec6c7f9a7..e4e6cf73c7e23 100644
--- a/compiler/rustc_typeck/src/check/intrinsic.rs
+++ b/compiler/rustc_typeck/src/check/intrinsic.rs
@@ -63,8 +63,6 @@ pub fn intrinsic_operation_unsafety(intrinsic: Symbol) -> hir::Unsafety {
         | sym::min_align_of
         | sym::needs_drop
         | sym::caller_location
-        | sym::size_of_val
-        | sym::min_align_of_val
         | sym::add_with_overflow
         | sym::sub_with_overflow
         | sym::mul_with_overflow
diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index 971ec5d9c8d64..64cf5286eb14a 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -4,6 +4,7 @@
 //! types, initializing and manipulating memory.
 
 #![stable(feature = "rust1", since = "1.0.0")]
+#![cfg_attr(bootstrap, allow(unused_unsafe))]
 
 use crate::clone;
 use crate::cmp;
@@ -333,7 +334,8 @@ pub const fn size_of<T>() -> usize {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_size_of_val", issue = "46571")]
 pub const fn size_of_val<T: ?Sized>(val: &T) -> usize {
-    intrinsics::size_of_val(val)
+    // SAFETY: `val` is a reference, so it's a valid raw pointer
+    unsafe { intrinsics::size_of_val(val) }
 }
 
 /// Returns the size of the pointed-to value in bytes.
@@ -381,7 +383,8 @@ pub const fn size_of_val<T: ?Sized>(val: &T) -> usize {
 #[unstable(feature = "layout_for_ptr", issue = "69835")]
 #[rustc_const_unstable(feature = "const_size_of_val_raw", issue = "46571")]
 pub const unsafe fn size_of_val_raw<T: ?Sized>(val: *const T) -> usize {
-    intrinsics::size_of_val(val)
+    // SAFETY: the caller must provide a valid raw pointer
+    unsafe { intrinsics::size_of_val(val) }
 }
 
 /// Returns the [ABI]-required minimum alignment of a type.
@@ -425,7 +428,8 @@ pub fn min_align_of<T>() -> usize {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_deprecated(reason = "use `align_of_val` instead", since = "1.2.0")]
 pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
-    intrinsics::min_align_of_val(val)
+    // SAFETY: val is a reference, so it's a valid raw pointer
+    unsafe { intrinsics::min_align_of_val(val) }
 }
 
 /// Returns the [ABI]-required minimum alignment of a type.
@@ -469,7 +473,8 @@ pub const fn align_of<T>() -> usize {
 #[rustc_const_unstable(feature = "const_align_of_val", issue = "46571")]
 #[allow(deprecated)]
 pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
-    intrinsics::min_align_of_val(val)
+    // SAFETY: val is a reference, so it's a valid raw pointer
+    unsafe { intrinsics::min_align_of_val(val) }
 }
 
 /// Returns the [ABI]-required minimum alignment of the type of the value that `val` points to.
@@ -513,7 +518,8 @@ pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
 #[unstable(feature = "layout_for_ptr", issue = "69835")]
 #[rustc_const_unstable(feature = "const_align_of_val_raw", issue = "46571")]
 pub const unsafe fn align_of_val_raw<T: ?Sized>(val: *const T) -> usize {
-    intrinsics::min_align_of_val(val)
+    // SAFETY: the caller must provide a valid raw pointer
+    unsafe { intrinsics::min_align_of_val(val) }
 }
 
 /// Returns `true` if dropping values of type `T` matters.