Added quick fix to prevent zero-width constant expressions from being translated.

Author: sdleffler

src/librustc_trans/trans/expr.rs

@@ -151,9 +151,9 @@ pub fn trans_into<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
             }
 
             // If we see a const here, that's because it evaluates to a type with zero size. We
-            // should be able to just discard it.
-            // FIXME: Check the type of the expression and see if it's a zero-size type instead of
-            // this hack.
+            // should be able to just discard it, since const expressions are guaranteed not to
+            // have side effects. This seems to be reached through tuple struct constructors being
+            // passed zero-size constants.
             if let hir::ExprPath(..) = expr.node {
                 match bcx.def(expr.id) {
                     Def::Const(_) | Def::AssociatedConst(_) => {