Rollup merge of #66059 - RalfJung:panic-on-non-zero, r=eddyb

mem::zeroed/uninit: panic on types that do not permit zero-initialization

r? @eddyb @oli-obk

Cc https://github.com/rust-lang/rust/issues/62825

Also see [this summary comment](https://github.com/rust-lang/rust/pull/66059#issuecomment-586734747)

2 files changed, 16 insertions, 0 deletions

diff --git a/src/libcore/intrinsics.rs b/src/libcore/intrinsics.rs
index a889eff75c0..721a2d26a71 100644
--- a/src/libcore/intrinsics.rs
+++ b/src/libcore/intrinsics.rs
@@ -1007,6 +1007,16 @@ extern "rust-intrinsic" {
     /// This will statically either panic, or do nothing.
     pub fn panic_if_uninhabited<T>();
 
+    /// A guard for unsafe functions that cannot ever be executed if `T` does not permit
+    /// zero-initialization: This will statically either panic, or do nothing.
+    #[cfg(not(bootstrap))]
+    pub fn panic_if_zero_invalid<T>();
+
+    /// A guard for unsafe functions that cannot ever be executed if `T` has invalid
+    /// bit patterns: This will statically either panic, or do nothing.
+    #[cfg(not(bootstrap))]
+    pub fn panic_if_any_invalid<T>();
+
     /// Gets a reference to a static `Location` indicating where it was called.
     #[rustc_const_unstable(feature = "const_caller_location", issue = "47809")]
     pub fn caller_location() -> &'static crate::panic::Location<'static>;
diff --git a/src/libcore/mem/mod.rs b/src/libcore/mem/mod.rs
index 90144d11dc9..8add875dcbe 100644
--- a/src/libcore/mem/mod.rs
+++ b/src/libcore/mem/mod.rs
@@ -496,6 +496,9 @@ pub const fn needs_drop<T>() -> bool {
 #[allow(deprecated)]
 #[rustc_diagnostic_item = "mem_zeroed"]
 pub unsafe fn zeroed<T>() -> T {
+    #[cfg(not(bootstrap))]
+    intrinsics::panic_if_zero_invalid::<T>();
+    #[cfg(bootstrap)]
     intrinsics::panic_if_uninhabited::<T>();
     intrinsics::init()
 }
@@ -529,6 +532,9 @@ pub unsafe fn zeroed<T>() -> T {
 #[allow(deprecated)]
 #[rustc_diagnostic_item = "mem_uninitialized"]
 pub unsafe fn uninitialized<T>() -> T {
+    #[cfg(not(bootstrap))]
+    intrinsics::panic_if_any_invalid::<T>();
+    #[cfg(bootstrap)]
     intrinsics::panic_if_uninhabited::<T>();
     intrinsics::uninit()
 }