gh-106529: Support JUMP_BACKWARD in Tier 2 (uops) (#106543)

During superblock generation, a JUMP_BACKWARD instruction is translated to either a JUMP_TO_TOP micro-op (when the target of the jump is exactly the beginning of the superblock, closing the loop), or a SAVE_IP + EXIT_TRACE pair, when the jump goes elsewhere.

The new JUMP_TO_TOP instruction includes a CHECK_EVAL_BREAKER() call, so a closed loop can still be interrupted.

1 files changed, 13 insertions, 2 deletions

diff --git a/Python/optimizer.c b/Python/optimizer.c
index 08073193c02..8d4162b44c2 100644
--- a/Python/optimizer.c
+++ b/Python/optimizer.c
@@ -372,9 +372,7 @@ translate_bytecode_to_trace(
     _PyUOpInstruction *trace,
     int buffer_size)
 {
-#ifdef Py_DEBUG
     _Py_CODEUNIT *initial_instr = instr;
-#endif
     int trace_length = 0;
     int max_length = buffer_size;
 
@@ -456,6 +454,19 @@ translate_bytecode_to_trace(
                 break;
             }
 
+            case JUMP_BACKWARD:
+            {
+                if (instr + 2 - oparg == initial_instr
+                    && trace_length + 3 <= max_length)
+                {
+                    ADD_TO_TRACE(JUMP_TO_TOP, 0);
+                }
+                else {
+                    DPRINTF(2, "JUMP_BACKWARD not to top ends trace\n");
+                }
+                goto done;
+            }
+
             default:
             {
                 const struct opcode_macro_expansion *expansion = &_PyOpcode_macro_expansion[opcode];