Fix invalid_upcast_comparisons lint for same size sign casts

clippy_lints/src/utils/mod.rs

@@ -9,6 +9,7 @@ use rustc::traits::Reveal;
 use rustc::traits;
 use rustc::ty::subst::Subst;
 use rustc::ty;
+use rustc::ty::layout::TargetDataLayout;
 use rustc_errors;
 use std::borrow::Cow;
 use std::env;
@@ -972,3 +973,9 @@ pub fn is_try(expr: &Expr) -> Option<&Expr> {
 
     None
 }
+
+pub fn type_size<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, ty: ty::Ty<'tcx>) -> Option<u64> {
+    cx.tcx.infer_ctxt((), Reveal::All).enter(|infcx|
+        ty.layout(&infcx).ok().map(|lay| lay.size(&TargetDataLayout::parse(cx.sess())).bytes())
+    )
+}