gh-106529: Implement JUMP_FORWARD in uops (with test) (#106651)

Note that this may generate two SAVE_IP uops in a row.
Removing unneeded SAVE_IP uops is the optimizer's job.

Author: gvanrossum

Lib/test/test_capi/test_misc.py

@@ -2553,6 +2553,7 @@ def testfunc(n):
             i = 0
             while i < n:
                 i += 1
+
         opt = _testinternalcapi.get_uop_optimizer()
         with temporary_optimizer(opt):
             testfunc(10)
@@ -2562,6 +2563,30 @@ def testfunc(n):
         uops = {opname for opname, _ in ex}
         self.assertIn("JUMP_TO_TOP", uops)
 
+    def test_jump_forward(self):
+        def testfunc(n):
+            a = 0
+            while a < n:
+                if a < 0:
+                    a = -a
+                else:
+                    a = +a
+                a += 1
+            return a
+
+        opt = _testinternalcapi.get_uop_optimizer()
+        with temporary_optimizer(opt):
+            testfunc(10)
+
+        ex = get_first_executor(testfunc)
+        self.assertIsNotNone(ex)
+        # for i, (opname, oparg) in enumerate(ex):
+        #     print(f"{i:4d}: {opname:<20s} {oparg:4d}")
+        uops = {opname for opname, _ in ex}
+        # Since there is no JUMP_FORWARD instruction,
+        # look for indirect evidence: the += operator
+        self.assertIn("_BINARY_OP_ADD_INT", uops)
+
 
 if __name__ == "__main__":
     unittest.main()

Python/optimizer.c

@@ -472,6 +472,13 @@ translate_bytecode_to_trace(
                 goto done;
             }
 
+            case JUMP_FORWARD:
+            {
+                // This will emit two SAVE_IP instructions; leave it to the optimizer
+                instr += oparg;
+                break;
+            }
+
             default:
             {
                 const struct opcode_macro_expansion *expansion = &_PyOpcode_macro_expansion[opcode];