Rollup merge of #51839 - oli-obk:const_shift_overflow, r=nikomatsakis

Detect overflows of non u32 shifts

src/librustc_mir/interpret/operator.rs

@@ -95,9 +95,10 @@ impl<'a, 'mir, 'tcx, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M> {
         // These ops can have an RHS with a different numeric type.
         if right_kind.is_int() && (bin_op == Shl || bin_op == Shr) {
             let signed = left_layout.abi.is_signed();
+            let mut oflo = (r as u32 as u128) != r;
             let mut r = r as u32;
             let size = left_layout.size.bits() as u32;
-            let oflo = r >= size;
+            oflo |= r >= size;
             if oflo {
                 r %= size;
             }

src/test/ui/const-eval/shift_overflow.rs

@@ -0,0 +1,19 @@
+// Copyright 2018 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.
+
+enum Foo {
+    // test that we detect overflows for non-u32 discriminants
+    X = 1 << ((u32::max_value() as u64) + 1), //~ ERROR E0080
+    Y = 42,
+}
+
+
+fn main() {
+}

src/test/ui/const-eval/shift_overflow.stderr

@@ -0,0 +1,9 @@
+error[E0080]: could not evaluate enum discriminant
+  --> $DIR/shift_overflow.rs:13:9
+   |
+LL |     X = 1 << ((u32::max_value() as u64) + 1), //~ ERROR E0080
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ attempt to shift left with overflow
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.