From 1a7b00d5fd28edc3ea236bbe8e5fe0b5d81b4c8c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20K=C3=A5re=20Alsaker?= <john.kare.alsaker@gmail.com>
Date: Mon, 8 Jan 2018 13:18:50 +0100
Subject: [PATCH] Don't look for niches inside generator types. Fixes #47253

---
 src/librustc/ty/layout.rs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/librustc/ty/layout.rs b/src/librustc/ty/layout.rs
index 34a7d4ad7cf..50efb730037 100644
--- a/src/librustc/ty/layout.rs
+++ b/src/librustc/ty/layout.rs
@@ -2295,6 +2295,13 @@ impl<'a, 'tcx> TyLayout<'tcx> {
             }, niche_start))
         };
 
+        // Locals variables which live across yields are stored
+        // in the generator type as fields. These may be uninitialized
+        // so we don't look for niches there.
+        if let ty::TyGenerator(..) = self.ty.sty {
+            return Ok(None);
+        }
+
         match self.abi {
             Abi::Scalar(ref scalar) => {
                 return Ok(scalar_component(scalar, Size::from_bytes(0)));