do not claim that transmute is like memcpy

1 files changed, 3 insertions, 2 deletions

diff --git a/library/core/src/intrinsics.rs b/library/core/src/intrinsics.rs
index dc82b32214c..6bf95a1b008 100644
--- a/library/core/src/intrinsics.rs
+++ b/library/core/src/intrinsics.rs
@@ -1212,8 +1212,9 @@ extern "rust-intrinsic" {
     ///
     /// `transmute` is semantically equivalent to a bitwise move of one type
     /// into another. It copies the bits from the source value into the
-    /// destination value, then forgets the original. It's equivalent to C's
-    /// `memcpy` under the hood, just like `transmute_copy`.
+    /// destination value, then forgets the original. Note that source and destination
+    /// are passed by-value, which means if `T` or `U` contains padding, that padding
+    /// might *not* be preserved by `transmute`.
     ///
     /// Because `transmute` is a by-value operation, alignment of the *transmuted values
     /// themselves* is not a concern. As with any other function, the compiler already ensures