gh-104584: Baby steps towards generating and executing traces (#105924)

Added a new, experimental, tracing optimizer and interpreter (a.k.a. "tier 2"). This currently pessimizes, so don't use yet -- this is infrastructure so we can experiment with optimizing passes. To enable it, pass ``-Xuops`` or set ``PYTHONUOPS=1``. To get debug output, set ``PYTHONUOPSDEBUG=N`` where ``N`` is a debug level (0-4, where 0 is no debug output and 4 is excessively verbose).

All of this code is likely to change dramatically before the 3.13 feature freeze. But this is a first step.

Author: gvanrossum

.gitattributes

@@ -86,6 +86,7 @@ Parser/token.c                                      generated
 Programs/test_frozenmain.h                          generated
 Python/Python-ast.c                                 generated
 Python/generated_cases.c.h                          generated
+Python/executor_cases.c.h                           generated
 Python/opcode_targets.h                             generated
 Python/stdlib_module_names.h                        generated
 Tools/peg_generator/pegen/grammar_parser.py         generated

Include/cpython/optimizer.h

@@ -45,6 +45,7 @@ extern _PyOptimizerObject _PyOptimizer_Default;
 
 /* For testing */
 PyAPI_FUNC(PyObject *)PyUnstable_Optimizer_NewCounter(void);
+PyAPI_FUNC(PyObject *)PyUnstable_Optimizer_NewUOpOptimizer(void);
 
 #define OPTIMIZER_BITS_IN_COUNTER 4
 

Include/internal/pycore_uops.h

@@ -0,0 +1,31 @@
+#ifndef Py_INTERNAL_UOPS_H
+#define Py_INTERNAL_UOPS_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+#define _Py_UOP_MAX_TRACE_LENGTH 16
+
+typedef struct {
+    int opcode;
+    uint64_t operand;  // Sometimes oparg, sometimes a cache entry
+} _PyUOpInstruction;
+
+typedef struct {
+    _PyExecutorObject base;
+    _PyUOpInstruction trace[_Py_UOP_MAX_TRACE_LENGTH];  // TODO: variable length
+} _PyUOpExecutorObject;
+
+_PyInterpreterFrame *_PyUopExecute(
+    _PyExecutorObject *executor,
+    _PyInterpreterFrame *frame,
+    PyObject **stack_pointer);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_UOPS_H */

Include/pystats.h

@@ -71,6 +71,9 @@ typedef struct _object_stats {
     uint64_t type_cache_dunder_misses;
     uint64_t type_cache_collisions;
     uint64_t optimization_attempts;
+    uint64_t optimization_traces_created;
+    uint64_t optimization_traces_executed;
+    uint64_t optimization_uops_executed;
 } ObjectStats;
 
 typedef struct _stats {

Makefile.pre.in

@@ -1542,19 +1542,9 @@ regen-opcode-targets:
 
 .PHONY: regen-cases
 regen-cases:
-	# Regenerate Python/generated_cases.c.h
-	# and Python/opcode_metadata.h
-	# from Python/bytecodes.c
-	# using Tools/cases_generator/generate_cases.py
+	# Regenerate various files from Python/bytecodes.c
 	PYTHONPATH=$(srcdir)/Tools/cases_generator \
-	$(PYTHON_FOR_REGEN) \
-	    $(srcdir)/Tools/cases_generator/generate_cases.py \
-		--emit-line-directives \
-		-o $(srcdir)/Python/generated_cases.c.h.new \
-		-m $(srcdir)/Python/opcode_metadata.h.new \
-		$(srcdir)/Python/bytecodes.c
-	$(UPDATE_FILE) $(srcdir)/Python/generated_cases.c.h $(srcdir)/Python/generated_cases.c.h.new
-	$(UPDATE_FILE) $(srcdir)/Python/opcode_metadata.h $(srcdir)/Python/opcode_metadata.h.new
+	$(PYTHON_FOR_REGEN) $(srcdir)/Tools/cases_generator/generate_cases.py -l
 
 Python/compile.o: $(srcdir)/Python/opcode_metadata.h
 
@@ -1565,6 +1555,13 @@ Python/ceval.o: \
 		$(srcdir)/Python/opcode_metadata.h \
 		$(srcdir)/Python/opcode_targets.h
 
+Python/flowgraph.o: \
+		$(srcdir)/Python/opcode_metadata.h
+
+Python/optimizer.o: \
+		$(srcdir)/Python/executor_cases.c.h \
+		$(srcdir)/Python/opcode_metadata.h
+
 Python/frozen.o: $(FROZEN_FILES_OUT)
 
 # Generate DTrace probe macros, then rename them (PYTHON_ -> PyDTrace_) to

Misc/NEWS.d/next/Core and Builtins/2023-06-27-00-58-26.gh-issue-104584.Wu-uXy.rst

@@ -0,0 +1 @@
+Added a new, experimental, tracing optimizer and interpreter (a.k.a. "tier 2"). This currently pessimizes, so don't use yet -- this is infrastructure so we can experiment with optimizing passes. To enable it, pass ``-Xuops`` or set ``PYTHONUOPS=1``. To get debug output, set ``PYTHONUOPSDEBUG=N`` where ``N`` is a debug level (0-4, where 0 is no debug output and 4 is excessively verbose).

Modules/_testinternalcapi.c

@@ -830,6 +830,12 @@ get_counter_optimizer(PyObject *self, PyObject *arg)
     return PyUnstable_Optimizer_NewCounter();
 }
 
+static PyObject *
+get_uop_optimizer(PyObject *self, PyObject *arg)
+{
+    return PyUnstable_Optimizer_NewUOpOptimizer();
+}
+
 static PyObject *
 set_optimizer(PyObject *self, PyObject *opt)
 {
@@ -994,6 +1000,7 @@ static PyMethodDef module_functions[] = {
     {"get_optimizer", get_optimizer,  METH_NOARGS, NULL},
     {"set_optimizer", set_optimizer,  METH_O, NULL},
     {"get_counter_optimizer", get_counter_optimizer, METH_NOARGS, NULL},
+    {"get_uop_optimizer", get_uop_optimizer, METH_NOARGS, NULL},
     {"pending_threadfunc", _PyCFunction_CAST(pending_threadfunc),
      METH_VARARGS | METH_KEYWORDS},
 //    {"pending_fd_identify", pending_fd_identify, METH_VARARGS, NULL},

Python/bytecodes.c

@@ -52,8 +52,6 @@
 #define family(name, ...) static int family_##name
 #define pseudo(name) static int pseudo_##name
 
-typedef PyObject *(*convertion_func_ptr)(PyObject *);
-
 // Dummy variables for stack effects.
 static PyObject *value, *value1, *value2, *left, *right, *res, *sum, *prod, *sub;
 static PyObject *container, *start, *stop, *v, *lhs, *rhs, *res2;
@@ -2182,7 +2180,7 @@ dummy_func(
             frame = executor->execute(executor, frame, stack_pointer);
             if (frame == NULL) {
                 frame = cframe.current_frame;
-                goto error;
+                goto resume_with_error;
             }
             goto resume_frame;
         }

Python/ceval.c

@@ -22,6 +22,7 @@
 #include "pycore_sysmodule.h"     // _PySys_Audit()
 #include "pycore_tuple.h"         // _PyTuple_ITEMS()
 #include "pycore_typeobject.h"    // _PySuper_Lookup()
+#include "pycore_uops.h"          // _PyUOpExecutorObject
 #include "pycore_emscripten_signal.h"  // _Py_CHECK_EMSCRIPTEN_SIGNALS
 
 #include "pycore_dict.h"
@@ -223,14 +224,6 @@ _PyEvalFramePushAndInit_Ex(PyThreadState *tstate, PyFunctionObject *func,
 static void
 _PyEvalFrameClearAndPop(PyThreadState *tstate, _PyInterpreterFrame *frame);
 
-typedef PyObject *(*convertion_func_ptr)(PyObject *);
-
-static const convertion_func_ptr CONVERSION_FUNCTIONS[4] = {
-    [FVC_STR] = PyObject_Str,
-    [FVC_REPR] = PyObject_Repr,
-    [FVC_ASCII] = PyObject_ASCII
-};
-
 #define UNBOUNDLOCAL_ERROR_MSG \
     "cannot access local variable '%s' where it is not associated with a value"
 #define UNBOUNDFREE_ERROR_MSG \
@@ -2771,3 +2764,131 @@ void Py_LeaveRecursiveCall(void)
 {
     _Py_LeaveRecursiveCall();
 }
+
+///////////////////// Experimental UOp Interpreter /////////////////////
+
+// UPDATE_MISS_STATS (called by DEOPT_IF) uses next_instr
+// TODO: Make it do something useful
+#undef UPDATE_MISS_STATS
+#define UPDATE_MISS_STATS(INSTNAME) ((void)0)
+
+_PyInterpreterFrame *
+_PyUopExecute(_PyExecutorObject *executor, _PyInterpreterFrame *frame, PyObject **stack_pointer)
+{
+#ifdef LLTRACE
+    char *uop_debug = Py_GETENV("PYTHONUOPSDEBUG");
+    int lltrace = 0;
+    if (uop_debug != NULL && *uop_debug >= '0') {
+        lltrace = *uop_debug - '0';  // TODO: Parse an int and all that
+    }
+    if (lltrace >= 2) {
+        PyCodeObject *code = _PyFrame_GetCode(frame);
+        _Py_CODEUNIT *instr = frame->prev_instr + 1;
+        fprintf(stderr,
+                "Entering _PyUopExecute for %s (%s:%d) at offset %ld\n",
+                PyUnicode_AsUTF8(code->co_qualname),
+                PyUnicode_AsUTF8(code->co_filename),
+                code->co_firstlineno,
+                (long)(instr - (_Py_CODEUNIT *)code->co_code_adaptive));
+    }
+#endif
+
+    PyThreadState *tstate = _PyThreadState_GET();
+    _PyUOpExecutorObject *self = (_PyUOpExecutorObject *)executor;
+
+    // Equivalent to CHECK_EVAL_BREAKER()
+    _Py_CHECK_EMSCRIPTEN_SIGNALS_PERIODICALLY();
+    if (_Py_atomic_load_relaxed_int32(&tstate->interp->ceval.eval_breaker)) {
+        if (_Py_HandlePending(tstate) != 0) {
+            goto error;
+        }
+    }
+
+    OBJECT_STAT_INC(optimization_traces_executed);
+    _Py_CODEUNIT *ip_offset = (_Py_CODEUNIT *)_PyFrame_GetCode(frame)->co_code_adaptive - 1;
+    int pc = 0;
+    int opcode;
+    uint64_t operand;
+    int oparg;
+    for (;;) {
+        opcode = self->trace[pc].opcode;
+        operand = self->trace[pc].operand;
+        oparg = (int)operand;
+#ifdef LLTRACE
+        if (lltrace >= 3) {
+            const char *opname = opcode < 256 ? _PyOpcode_OpName[opcode] : "";
+            int stack_level = (int)(stack_pointer - _PyFrame_Stackbase(frame));
+            fprintf(stderr, "  uop %s %d, operand %" PRIu64 ", stack_level %d\n",
+                    opname, opcode, operand, stack_level);
+        }
+#endif
+        pc++;
+        OBJECT_STAT_INC(optimization_uops_executed);
+        switch (opcode) {
+
+#undef ENABLE_SPECIALIZATION
+#define ENABLE_SPECIALIZATION 0
+#include "executor_cases.c.h"
+
+            case SET_IP:
+            {
+                frame->prev_instr = ip_offset + oparg;
+                break;
+            }
+
+            case EXIT_TRACE:
+            {
+                _PyFrame_SetStackPointer(frame, stack_pointer);
+                Py_DECREF(self);
+                return frame;
+            }
+
+            default:
+            {
+                fprintf(stderr, "Unknown uop %d, operand %" PRIu64 "\n", opcode, operand);
+                Py_FatalError("Unknown uop");
+                abort();  // Unreachable
+                for (;;) {}
+                // Really unreachable
+            }
+
+        }
+    }
+
+pop_4_error:
+    STACK_SHRINK(1);
+pop_3_error:
+    STACK_SHRINK(1);
+pop_2_error:
+    STACK_SHRINK(1);
+pop_1_error:
+    STACK_SHRINK(1);
+error:
+    // On ERROR_IF we return NULL as the frame.
+    // The caller recovers the frame from cframe.current_frame.
+#ifdef LLTRACE
+    if (lltrace >= 2) {
+        fprintf(stderr, "Error: [Opcode %d, operand %" PRIu64 "]\n", opcode, operand);
+    }
+#endif
+    _PyFrame_SetStackPointer(frame, stack_pointer);
+    Py_DECREF(self);
+    return NULL;
+
+PREDICTED(UNPACK_SEQUENCE)
+PREDICTED(COMPARE_OP)
+PREDICTED(LOAD_SUPER_ATTR)
+PREDICTED(STORE_SUBSCR)
+PREDICTED(BINARY_SUBSCR)
+PREDICTED(BINARY_OP)
+    // On DEOPT_IF we just repeat the last instruction.
+    // This presumes nothing was popped from the stack (nor pushed).
+#ifdef LLTRACE
+    if (lltrace >= 2) {
+        fprintf(stderr, "DEOPT: [Opcode %d, operand %" PRIu64 "]\n", opcode, operand);
+    }
+#endif
+    _PyFrame_SetStackPointer(frame, stack_pointer);
+    Py_DECREF(self);
+    return frame;
+}

Python/ceval_macros.h

@@ -1,4 +1,4 @@
-// Macros needed by ceval.c and bytecodes.c
+// Macros and other things needed by ceval.c and bytecodes.c
 
 /* Computed GOTOs, or
        the-optimization-commonly-but-improperly-known-as-"threaded code"
@@ -339,3 +339,11 @@ do { \
         goto error; \
     } \
 } while (0);
+
+typedef PyObject *(*convertion_func_ptr)(PyObject *);
+
+static const convertion_func_ptr CONVERSION_FUNCTIONS[4] = {
+    [FVC_STR] = PyObject_Str,
+    [FVC_REPR] = PyObject_Repr,
+    [FVC_ASCII] = PyObject_ASCII
+};