Auto merge of #32285 - oli-obk:fix/const_bitshift, r=eddyb

const eval: don't assume the rhs of a bitshift is of any particular type

[regression found](https://internals.rust-lang.org/t/regression-report-stable-2016-03-03-vs-nightly-2016-03-15/3250) in jpeg-decoder

src/librustc/middle/const_eval.rs

@@ -671,7 +671,7 @@ pub fn eval_const_expr_partial<'tcx>(tcx: &TyCtxt<'tcx>,
       }
       hir::ExprBinary(op, ref a, ref b) => {
         let b_ty = match op.node {
-            hir::BiShl | hir::BiShr => ty_hint.checked_or(tcx.types.usize),
+            hir::BiShl | hir::BiShr => ty_hint.erase_hint(),
             _ => ty_hint
         };
         // technically, if we don't have type hints, but integral eval

src/test/run-pass/const-bitshift-rhs-inference.rs

+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+const RHS: u8 = 8;
+const IRHS: i8 = 8;
+const RHS16: u16 = 8;
+const IRHS16: i16 = 8;
+const RHS32: u32 = 8;
+const IRHS32: i32 = 8;
+const RHS64: u64 = 8;
+const IRHS64: i64 = 8;
+const RHSUS: usize = 8;
+const IRHSIS: isize = 8;
+
+fn main() {
+    let _: [&'static str; 1 << RHS] = [""; 256];
+    let _: [&'static str; 1 << IRHS] = [""; 256];
+    let _: [&'static str; 1 << RHS16] = [""; 256];
+    let _: [&'static str; 1 << IRHS16] = [""; 256];
+    let _: [&'static str; 1 << RHS32] = [""; 256];
+    let _: [&'static str; 1 << IRHS32] = [""; 256];
+    let _: [&'static str; 1 << RHS64] = [""; 256];
+    let _: [&'static str; 1 << IRHS64] = [""; 256];
+    let _: [&'static str; 1 << RHSUS] = [""; 256];
+    let _: [&'static str; 1 << IRHSIS] = [""; 256];
+}