From f03b18b99b683c25a584344f73cdf9704d77b719 Mon Sep 17 00:00:00 2001
From: oli <github35764891676564198441@oli-obk.de>
Date: Sun, 1 Nov 2020 17:17:04 +0000
Subject: [PATCH] Add `is_null` helper

This is cheaper than creating a null-`ScalarInt` and comparing
and then just throwing it away.
---
 compiler/rustc_middle/src/ty/consts/int.rs   | 5 +++++
 compiler/rustc_mir/src/const_eval/machine.rs | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_middle/src/ty/consts/int.rs b/compiler/rustc_middle/src/ty/consts/int.rs
index 838e9819b0fcd..89d9ba2c0c34b 100644
--- a/compiler/rustc_middle/src/ty/consts/int.rs
+++ b/compiler/rustc_middle/src/ty/consts/int.rs
@@ -188,6 +188,11 @@ impl ScalarInt {
         Self { data: 0, size: size.bytes() as u8 }
     }
 
+    #[inline]
+    pub fn is_null(self) -> bool {
+        self.data == 0
+    }
+
     pub(crate) fn ptr_sized_op<'tcx>(
         self,
         dl: &TargetDataLayout,
diff --git a/compiler/rustc_mir/src/const_eval/machine.rs b/compiler/rustc_mir/src/const_eval/machine.rs
index 5fe393bf43235..c72089ec55a99 100644
--- a/compiler/rustc_mir/src/const_eval/machine.rs
+++ b/compiler/rustc_mir/src/const_eval/machine.rs
@@ -1,6 +1,6 @@
 use rustc_middle::mir;
 use rustc_middle::ty::layout::HasTyCtxt;
-use rustc_middle::ty::{self, ScalarInt, Ty};
+use rustc_middle::ty::{self, Ty};
 use std::borrow::Borrow;
 use std::collections::hash_map::Entry;
 use std::hash::Hash;
@@ -199,7 +199,7 @@ impl<'mir, 'tcx: 'mir> CompileTimeEvalContext<'mir, 'tcx> {
             // is in bounds, because if they are in bounds, the pointer can't be null.
             // Inequality with integers other than null can never be known for sure.
             (Scalar::Int(int), Scalar::Ptr(ptr)) | (Scalar::Ptr(ptr), Scalar::Int(int)) => {
-                int == ScalarInt::null(int.size()) && !self.memory.ptr_may_be_null(ptr)
+                int.is_null() && !self.memory.ptr_may_be_null(ptr)
             }
             // FIXME: return `true` for at least some comparisons where we can reliably
             // determine the result of runtime inequality tests at compile-time.