From a3cd293148e0678074cbbec06e5d3e9159a14ea0 Mon Sep 17 00:00:00 2001
From: bjorn3 <bjorn3@users.noreply.github.com>
Date: Wed, 24 Jun 2020 12:10:20 +0200
Subject: [PATCH] Don't perform a double substitution in some cases

---
 src/common.rs | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/common.rs b/src/common.rs
index ec58a7d3d29..1d69018be50 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -305,13 +305,17 @@ fn target_spec(&self) -> &Target {
 impl<'tcx, B: Backend + 'static> FunctionCx<'_, 'tcx, B> {
     pub(crate) fn monomorphize<T>(&self, value: &T) -> T
     where
-        T: TypeFoldable<'tcx>,
+        T: TypeFoldable<'tcx> + Copy,
     {
-        self.tcx.subst_and_normalize_erasing_regions(
-            self.instance.substs,
-            ty::ParamEnv::reveal_all(),
-            value,
-        )
+        if let Some(substs) = self.instance.substs_for_mir_body() {
+            self.tcx.subst_and_normalize_erasing_regions(
+                substs,
+                ty::ParamEnv::reveal_all(),
+                value,
+            )
+        } else {
+            self.tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), *value)
+        }
     }
 
     pub(crate) fn clif_type(&self, ty: Ty<'tcx>) -> Option<Type> {
-- 
2.44.0