GH-118095: Allow a variant of RESUME_CHECK in tier 2 (GH-118286)

4 files changed, 77 insertions, 1 deletions

diff --git a/Python/bytecodes.c b/Python/bytecodes.c
index fe3d613..f688856 100644
--- a/Python/bytecodes.c
+++ b/Python/bytecodes.c
@@ -4258,6 +4258,29 @@ dummy_func(
         }
 
 
+        /* Special version of RESUME_CHECK that (when paired with _EVAL_BREAKER_EXIT)
+         * is safe for tier 2. Progress is guaranteed because _EVAL_BREAKER_EXIT calls
+         * _Py_HandlePending which clears the eval_breaker so that _TIER2_RESUME_CHECK
+         * will not exit if it is immediately executed again. */
+        tier2 op(_TIER2_RESUME_CHECK, (--)) {
+#if defined(__EMSCRIPTEN__)
+            EXIT_IF(_Py_emscripten_signal_clock == 0);
+            _Py_emscripten_signal_clock -= Py_EMSCRIPTEN_SIGNAL_HANDLING;
+#endif
+            uintptr_t eval_breaker = _Py_atomic_load_uintptr_relaxed(&tstate->eval_breaker);
+            EXIT_IF(eval_breaker & _PY_EVAL_EVENTS_MASK);
+            assert(eval_breaker == FT_ATOMIC_LOAD_UINTPTR_ACQUIRE(_PyFrame_GetCode(frame)->_co_instrumentation_version));
+        }
+
+        tier2 op(_EVAL_BREAKER_EXIT, (--)) {
+            _Py_CHECK_EMSCRIPTEN_SIGNALS_PERIODICALLY();
+            QSBR_QUIESCENT_STATE(tstate);
+            if (_Py_HandlePending(tstate) != 0) {
+                GOTO_UNWIND();
+            }
+            EXIT_TO_TRACE();
+        }
+
 // END BYTECODES //
 
     }
diff --git a/Python/executor_cases.c.h b/Python/executor_cases.c.h
index 280cca1..2d9acfe 100644
--- a/Python/executor_cases.c.h
+++ b/Python/executor_cases.c.h
@@ -4295,4 +4295,31 @@
             break;
         }
 
+        case _TIER2_RESUME_CHECK: {
+            #if defined(__EMSCRIPTEN__)
+            if (_Py_emscripten_signal_clock == 0) {
+                UOP_STAT_INC(uopcode, miss);
+                JUMP_TO_JUMP_TARGET();
+            }
+            _Py_emscripten_signal_clock -= Py_EMSCRIPTEN_SIGNAL_HANDLING;
+            #endif
+            uintptr_t eval_breaker = _Py_atomic_load_uintptr_relaxed(&tstate->eval_breaker);
+            if (eval_breaker & _PY_EVAL_EVENTS_MASK) {
+                UOP_STAT_INC(uopcode, miss);
+                JUMP_TO_JUMP_TARGET();
+            }
+            assert(eval_breaker == FT_ATOMIC_LOAD_UINTPTR_ACQUIRE(_PyFrame_GetCode(frame)->_co_instrumentation_version));
+            break;
+        }
+
+        case _EVAL_BREAKER_EXIT: {
+            _Py_CHECK_EMSCRIPTEN_SIGNALS_PERIODICALLY();
+            QSBR_QUIESCENT_STATE(tstate);
+            if (_Py_HandlePending(tstate) != 0) {
+                GOTO_UNWIND();
+            }
+            EXIT_TO_TRACE();
+            break;
+        }
+
 #undef TIER_TWO
diff --git a/Python/optimizer.c b/Python/optimizer.c
index 02c9b39..fcd7d18 100644
--- a/Python/optimizer.c
+++ b/Python/optimizer.c
@@ -690,6 +690,12 @@ top:  // Jump here after _PUSH_FRAME or likely branches
                 break;
             }
 
+            case RESUME:
+                /* Use a special tier 2 version of RESUME_CHECK to allow traces to
+                 *  start with RESUME_CHECK */
+                ADD_TO_TRACE(_TIER2_RESUME_CHECK, 0, 0, target);
+                break;
+
             default:
             {
                 const struct opcode_macro_expansion *expansion = &_PyOpcode_macro_expansion[opcode];
@@ -967,7 +973,18 @@ prepare_for_execution(_PyUOpInstruction *buffer, int length)
         int32_t target = (int32_t)uop_get_target(inst);
         if (_PyUop_Flags[opcode] & (HAS_EXIT_FLAG | HAS_DEOPT_FLAG)) {
             if (target != current_jump_target) {
-                uint16_t exit_op = (_PyUop_Flags[opcode] & HAS_EXIT_FLAG) ? _SIDE_EXIT : _DEOPT;
+                uint16_t exit_op;
+                if (_PyUop_Flags[opcode] & HAS_EXIT_FLAG) {
+                    if (opcode == _TIER2_RESUME_CHECK) {
+                        exit_op = _EVAL_BREAKER_EXIT;
+                    }
+                    else {
+                        exit_op = _SIDE_EXIT;
+                    }
+                }
+                else {
+                    exit_op = _DEOPT;
+                }
                 make_exit(&buffer[next_spare], exit_op, target);
                 current_jump_target = target;
                 current_jump = next_spare;
@@ -1075,6 +1092,7 @@ sanity_check(_PyExecutorObject *executor)
         CHECK(
             opcode == _DEOPT ||
             opcode == _SIDE_EXIT ||
+            opcode == _EVAL_BREAKER_EXIT ||
             opcode == _ERROR_POP_N);
         if (opcode == _SIDE_EXIT) {
             CHECK(inst->format == UOP_FORMAT_EXIT);
diff --git a/Python/optimizer_cases.c.h b/Python/optimizer_cases.c.h
index b196568..4102d00 100644
--- a/Python/optimizer_cases.c.h
+++ b/Python/optimizer_cases.c.h
@@ -2145,3 +2145,11 @@
             break;
         }
 
+        case _TIER2_RESUME_CHECK: {
+            break;
+        }
+
+        case _EVAL_BREAKER_EXIT: {
+            break;
+        }
+