What if we don't do this in debug?

Author: scottmcm

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -403,30 +403,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 let cmp = bx.icmp(IntPredicate::IntEQ, discr_value, llval);
                 bx.cond_br_with_expect(cmp, lltarget, llotherwise, expect);
             }
-        } else if target_iter.len() == 2
-            && self.mir[targets.otherwise()].is_empty_unreachable()
-            && targets.all_values().contains(&Pu128(0))
-            && targets.all_values().contains(&Pu128(1))
-        {
-            // This is the really common case for `bool`, `Option`, etc.
-            // By using `trunc nuw` we communicate that other values are
-            // impossible without needing `switch` or `assume`s.
-            let true_bb = targets.target_for_value(1);
-            let false_bb = targets.target_for_value(0);
-            let true_ll = helper.llbb_with_cleanup(self, true_bb);
-            let false_ll = helper.llbb_with_cleanup(self, false_bb);
-            let true_cold = self.cold_blocks[true_bb];
-            let false_cold = self.cold_blocks[false_bb];
-            let expect = (true_cold != false_cold).then_some(!true_cold);
-
-            let bool_ty = bx.tcx().types.bool;
-            let cond = if switch_ty == bool_ty {
-                discr_value
-            } else {
-                let bool_llty = bx.immediate_backend_type(bx.layout_of(bool_ty));
-                bx.unchecked_utrunc(discr_value, bool_llty)
-            };
-            bx.cond_br_with_expect(cond, true_ll, false_ll, expect);
         } else if self.cx.sess().opts.optimize == OptLevel::No
             && target_iter.len() == 2
             && self.mir[targets.otherwise()].is_empty_unreachable()
@@ -451,6 +427,30 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             let llval = bx.const_uint_big(switch_llty, test_value1);
             let cmp = bx.icmp(IntPredicate::IntEQ, discr_value, llval);
             bx.cond_br(cmp, ll1, ll2);
+        } else if target_iter.len() == 2
+            && self.mir[targets.otherwise()].is_empty_unreachable()
+            && targets.all_values().contains(&Pu128(0))
+            && targets.all_values().contains(&Pu128(1))
+        {
+            // This is the really common case for `bool`, `Option`, etc.
+            // By using `trunc nuw` we communicate that other values are
+            // impossible without needing `switch` or `assume`s.
+            let true_bb = targets.target_for_value(1);
+            let false_bb = targets.target_for_value(0);
+            let true_ll = helper.llbb_with_cleanup(self, true_bb);
+            let false_ll = helper.llbb_with_cleanup(self, false_bb);
+            let true_cold = self.cold_blocks[true_bb];
+            let false_cold = self.cold_blocks[false_bb];
+            let expect = (true_cold != false_cold).then_some(!true_cold);
+
+            let bool_ty = bx.tcx().types.bool;
+            let cond = if switch_ty == bool_ty {
+                discr_value
+            } else {
+                let bool_llty = bx.immediate_backend_type(bx.layout_of(bool_ty));
+                bx.unchecked_utrunc(discr_value, bool_llty)
+            };
+            bx.cond_br_with_expect(cond, true_ll, false_ll, expect);
         } else {
             let otherwise = targets.otherwise();
             let otherwise_cold = self.cold_blocks[otherwise];