Add comparison operators to boolean const eval.

Author: Mark-Simulacrum

src/librustc_const_eval/eval.rs

@@ -732,6 +732,10 @@ pub fn eval_const_expr_partial<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
               hir::BiBitOr => a | b,
               hir::BiEq => a == b,
               hir::BiNe => a != b,
+              hir::BiLt => a < b,
+              hir::BiLe => a <= b,
+              hir::BiGe => a >= b,
+              hir::BiGt => a > b,
               _ => signal!(e, InvalidOpForBools(op.node)),
              })
           }

src/test/run-pass/const-err.rs

@@ -17,4 +17,8 @@ const X: *const u8 = b"" as _;
 fn main() {
     let _ = ((-1 as i8) << 8 - 1) as f32;
     let _ = 0u8 as char;
+    let _ = true > false;
+    let _ = true >= false;
+    let _ = true < false;
+    let _ = true >= false;
 }