From 67faea970857c292ae35dadd103287d4f4449a58 Mon Sep 17 00:00:00 2001
From: Aaron Patterson <tenderlove@ruby-lang.org>
Date: Mon, 7 Mar 2022 11:08:15 -0800
Subject: [PATCH] Small optimization for the opt_and instruction

This change eagerly performs a bitwise and on the parameters.  If both
parameters are fixnums, then the result value should also be a fixnum.
We can just test the bit on the result and return if it's a fixnum.
Otherwise return Qundef.
---
 vm_insnhelper.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 27d9d13aac..f6d9c2c634 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -5335,9 +5335,15 @@ vm_opt_ltlt(VALUE recv, VALUE obj)
 static VALUE
 vm_opt_and(VALUE recv, VALUE obj)
 {
-    if (FIXNUM_2_P(recv, obj) &&
+    // If recv and obj are both fixnums, then the bottom tag bit
+    // will be 1 on both.  1 & 1 == 1, so the result value will also
+    // be a fixnum.  If either side is *not* a fixnum, then the tag bit
+    // will be 0, and we return Qundef.
+    VALUE ret = ((SIGNED_VALUE) recv) & ((SIGNED_VALUE) obj);
+
+    if (FIXNUM_P(ret) &&
         BASIC_OP_UNREDEFINED_P(BOP_AND, INTEGER_REDEFINED_OP_FLAG)) {
-        return (recv & obj) | 1;
+        return ret;
     }
     else {
         return Qundef;