From d189cab027bee94f4a4ef09484e30354c9843764 Mon Sep 17 00:00:00 2001
From: gnzlbg <gonzalobg88@gmail.com>
Date: Tue, 26 Mar 2019 09:12:06 +0100
Subject: [PATCH] Use fallback on emscripten targets

---
 src/libcore/hint.rs | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/src/libcore/hint.rs b/src/libcore/hint.rs
index e73a1a2879347..856720bd55427 100644
--- a/src/libcore/hint.rs
+++ b/src/libcore/hint.rs
@@ -99,13 +99,29 @@ pub fn spin_loop() {
 /// This function is a no-op, and does not even read from `dummy`.
 #[unstable(feature = "test", issue = "27812")]
 pub fn black_box<T>(dummy: T) -> T {
-    #[cfg(not(target_arch = "asmjs"))] {
+    #[cfg(not(
+        any(
+            target_arch = "asmjs",
+            all(
+                target_arch = "wasm32",
+                target_os = "emscripten"
+            )
+        )
+    ))] {
         // we need to "use" the argument in some way LLVM can't
         // introspect.
         unsafe { asm!("" : : "r"(&dummy)) }
         dummy
     }
-    #[cfg(target_arch = "asmjs")] {
+    #[cfg(
+        any(
+            target_arch = "asmjs",
+            all(
+                target_arch = "wasm32",
+                target_os = "emscripten"
+            )
+        )
+    )] {
         unsafe {
             let ret = crate::ptr::read_volatile(&dummy);
             crate::mem::forget(dummy);