From 4cbe13adabc172f2f4bc40ca7590804d1378a22d Mon Sep 17 00:00:00 2001
From: Jakob Degen <jakob.e.degen@gmail.com>
Date: Tue, 5 Apr 2022 17:22:31 -0400
Subject: [PATCH] Document semantics of `Deinit` and `SetDiscriminant` MIR
 statements

---
 compiler/rustc_middle/src/mir/mod.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index 3832025f0385..578fcd82ad61 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -1588,8 +1588,15 @@ pub enum StatementKind<'tcx> {
     FakeRead(Box<(FakeReadCause, Place<'tcx>)>),
 
     /// Write the discriminant for a variant to the enum Place.
+    ///
+    /// This is permitted for both generators and ADTs. This does not necessarily write to the
+    /// entire place; instead, it writes to the minimum set of bytes as required by the layout for
+    /// the type.
     SetDiscriminant { place: Box<Place<'tcx>>, variant_index: VariantIdx },
 
+    /// Deinitializes the place.
+    ///
+    /// This writes `uninit` bytes to the entire place.
     Deinit(Box<Place<'tcx>>),
 
     /// Start a live range for the storage of the local.