1 files changed, 65 insertions, 0 deletions
diff --git a/compiler/rustc_serialize/src/int_overflow.rs b/compiler/rustc_serialize/src/int_overflow.rs
new file mode 100644
index 00000000000..f2aac2ef711
--- /dev/null
+++ b/compiler/rustc_serialize/src/int_overflow.rs
@@ -0,0 +1,65 @@
+// This would belong to `rustc_data_structures`, but `rustc_serialize` needs it too.
+
+/// Addition, but only overflow checked when `cfg(debug_assertions)` is set
+/// instead of respecting `-Coverflow-checks`.
+///
+/// This exists for performance reasons, as we ship rustc with overflow checks.
+/// While overflow checks are perf neutral in almost all of the compiler, there
+/// are a few particularly hot areas where we don't want overflow checks in our
+/// dist builds. Overflow is still a bug there, so we want overflow check for
+/// builds with debug assertions.
+///
+/// That's a long way to say that this should be used in areas where overflow
+/// is a bug but overflow checking is too slow.
+pub trait DebugStrictAdd {
+    /// See [`DebugStrictAdd`].
+    fn debug_strict_add(self, other: Self) -> Self;
+}
+
+macro_rules! impl_debug_strict_add {
+    ($( $ty:ty )*) => {
+        $(
+            impl DebugStrictAdd for $ty {
+                fn debug_strict_add(self, other: Self) -> Self {
+                    if cfg!(debug_assertions) {
+                        self + other
+                    } else {
+                        self.wrapping_add(other)
+                    }
+                }
+            }
+        )*
+    };
+}
+
+/// See [`DebugStrictAdd`].
+pub trait DebugStrictSub {
+    /// See [`DebugStrictAdd`].
+    fn debug_strict_sub(self, other: Self) -> Self;
+}
+
+macro_rules! impl_debug_strict_sub {
+    ($( $ty:ty )*) => {
+        $(
+            impl DebugStrictSub for $ty {
+                fn debug_strict_sub(self, other: Self) -> Self {
+                    if cfg!(debug_assertions) {
+                        self - other
+                    } else {
+                        self.wrapping_sub(other)
+                    }
+                }
+            }
+        )*
+    };
+}
+
+impl_debug_strict_add! {
+    u8 u16 u32 u64 u128 usize
+    i8 i16 i32 i64 i128 isize
+}
+
+impl_debug_strict_sub! {
+    u8 u16 u32 u64 u128 usize
+    i8 i16 i32 i64 i128 isize
+}