From 74b17685fe6d73189dcaf105bc2f4405f6719e7b Mon Sep 17 00:00:00 2001
From: Gary Guo <gary@garyguo.net>
Date: Tue, 10 Aug 2021 11:50:33 +0100
Subject: [PATCH] Implement `black_box` using intrinsic

The new implementation allows some `memcpy`s to be optimized away,
so the uninit value in ui/sanitize/memory.rs is constructed directly
onto the return place. Therefore the sanitizer now says that the
value is allocated by `main` rather than `random`.
---
 src/intrinsics/mod.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/intrinsics/mod.rs b/src/intrinsics/mod.rs
index 86698460747..1c4d307fc50 100644
--- a/src/intrinsics/mod.rs
+++ b/src/intrinsics/mod.rs
@@ -1136,6 +1136,11 @@ pub(crate) fn codegen_intrinsic_call<'tcx>(
                 };
             ret.write_cvalue(fx, CValue::by_val(is_eq_value, ret.layout()));
         };
+
+        black_box, (c a) {
+            // FIXME implement black_box semantics
+            ret.write_cvalue(fx, a);
+        };
     }
 
     if let Some((_, dest)) = destination {