Remove asymmetry in JUMP_BACKWARD specialization

Author: brandtbucher

Python/bytecodes.c

@@ -2805,20 +2805,18 @@ dummy_func(
         tier1 op(_SPECIALIZE_JUMP_BACKWARD, (--)) {
         #if ENABLE_SPECIALIZATION
             if (this_instr->op.code == JUMP_BACKWARD) {
-                if (tstate->interp->jit) {
-                    this_instr->op.code = JUMP_BACKWARD_JIT;
-                    next_instr = this_instr;
-                    DISPATCH_SAME_OPARG();
-                }
-                this_instr->op.code = JUMP_BACKWARD_NO_JIT;
+                this_instr->op.code = tstate->interp->jit ? JUMP_BACKWARD_JIT : JUMP_BACKWARD_NO_JIT;
+                // Need to re-dispatch so the warmup counter isn't off by one:
+                next_instr = this_instr;
+                DISPATCH_SAME_OPARG();
             }
         #endif
         }
 
         tier1 op(_JIT, (--)) {
         #ifdef _Py_TIER2
             _Py_BackoffCounter counter = this_instr[1].counter;
-            if (backoff_counter_triggers(counter)) {
+            if (backoff_counter_triggers(counter) && this_instr->op.code == JUMP_BACKWARD_JIT) {
                 _Py_CODEUNIT *start = this_instr;
                 /* Back up over EXTENDED_ARGs so optimizer sees the whole instruction */
                 while (oparg > 255) {