Changed the checked unsinged add to use a simpler, but slighly slower implementation in debug mode.

Author: FractalFir

compiler/rustc_codegen_llvm/src/builder.rs

@@ -550,13 +550,17 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
                 Int(I32) => "llvm.sadd.with.overflow.i32",
                 Int(I64) => "llvm.sadd.with.overflow.i64",
                 Int(I128) => "llvm.sadd.with.overflow.i128",
-
+                Uint(_) if self.cx.sess().opts.optimize == OptLevel::No => {
+                    let sum = self.add(lhs, rhs);
+                    let ord = self.or(lhs, rhs);
+                    let cmp = self.icmp(IntPredicate::IntULT, sum, ord);
+                    return (sum, cmp);
+                }
                 Uint(U8) => "llvm.uadd.with.overflow.i8",
                 Uint(U16) => "llvm.uadd.with.overflow.i16",
                 Uint(U32) => "llvm.uadd.with.overflow.i32",
                 Uint(U64) => "llvm.uadd.with.overflow.i64",
                 Uint(U128) => "llvm.uadd.with.overflow.i128",
-
                 _ => unreachable!(),
             },
             OverflowOp::Sub => match new_kind {