GH-93516: Store offset of first traceable instruction in code object (GH-93769)

Author: markshannon

Include/cpython/code.h

@@ -89,6 +89,7 @@ typedef uint16_t _Py_CODEUNIT;
     PyObject *co_linetable;       /* bytes object that holds location info */  \
     PyObject *co_weakreflist;     /* to support weakrefs to code objects */    \
     void *_co_code;               /* cached co_code object/attribute */        \
+    int _co_firsttraceable;       /* index of first traceable instruction */   \
     /* Scratch space for extra data relating to the code object.               \
        Type is a void* to keep the format private in codeobject.c to force     \
        people to go through the proper APIs. */                                \

Lib/opcode.py

@@ -177,7 +177,7 @@ def jabs_op(name, op):
 hasfree.append(148)
 def_op('COPY_FREE_VARS', 149)
 def_op('YIELD_VALUE', 150)
-def_op('RESUME', 151)
+def_op('RESUME', 151)   # This must be kept in sync with deepfreeze.py
 def_op('MATCH_CLASS', 152)
 
 def_op('FORMAT_VALUE', 155)

Misc/NEWS.d/next/Core and Builtins/2022-06-13-13-55-34.gh-issue-93516.HILrDl.rst

@@ -0,0 +1,2 @@
+Store offset of first traceable instruction in code object to avoid having
+to recompute it for each instruction when tracing.

Objects/codeobject.c

@@ -339,6 +339,12 @@ init_code(PyCodeObject *co, struct _PyCodeConstructor *con)
     co->co_warmup = QUICKENING_INITIAL_WARMUP_VALUE;
     memcpy(_PyCode_CODE(co), PyBytes_AS_STRING(con->code),
            PyBytes_GET_SIZE(con->code));
+    int entry_point = 0;
+    while (entry_point < Py_SIZE(co) &&
+        _Py_OPCODE(_PyCode_CODE(co)[entry_point]) != RESUME) {
+        entry_point++;
+    }
+    co->_co_firsttraceable = entry_point;
 }
 
 static int

Python/ceval.c

@@ -5568,57 +5568,47 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, _PyInterpreterFrame *frame, int
         case DO_TRACING:
 #endif
     {
-        if (tstate->tracing == 0) {
+        if (tstate->tracing == 0 &&
+            INSTR_OFFSET() >= frame->f_code->_co_firsttraceable
+        ) {
             int instr_prev = _PyInterpreterFrame_LASTI(frame);
             frame->prev_instr = next_instr;
             TRACING_NEXTOPARG();
-            switch(opcode) {
-                case COPY_FREE_VARS:
-                case MAKE_CELL:
-                case RETURN_GENERATOR:
-                    /* Frame not fully initialized */
-                    break;
-                case RESUME:
-                    if (oparg < 2) {
-                        CHECK_EVAL_BREAKER();
-                    }
-                    /* Call tracing */
-                    TRACE_FUNCTION_ENTRY();
-                    DTRACE_FUNCTION_ENTRY();
-                    break;
-                case POP_TOP:
-                    if (_Py_OPCODE(next_instr[-1]) == RETURN_GENERATOR) {
-                        /* Frame not fully initialized */
-                        break;
-                    }
-                    /* fall through */
-                default:
-                    /* line-by-line tracing support */
-                    if (PyDTrace_LINE_ENABLED()) {
-                        maybe_dtrace_line(frame, &tstate->trace_info, instr_prev);
-                    }
-
-                    if (cframe.use_tracing &&
-                        tstate->c_tracefunc != NULL && !tstate->tracing) {
-                        int err;
-                        /* see maybe_call_line_trace()
-                        for expository comments */
-                        _PyFrame_SetStackPointer(frame, stack_pointer);
-
-                        err = maybe_call_line_trace(tstate->c_tracefunc,
-                                                    tstate->c_traceobj,
-                                                    tstate, frame, instr_prev);
-                        if (err) {
-                            /* trace function raised an exception */
-                            next_instr++;
-                            goto error;
-                        }
-                        /* Reload possibly changed frame fields */
-                        next_instr = frame->prev_instr;
+            if (opcode == RESUME) {
+                if (oparg < 2) {
+                    CHECK_EVAL_BREAKER();
+                }
+                /* Call tracing */
+                TRACE_FUNCTION_ENTRY();
+                DTRACE_FUNCTION_ENTRY();
+            }
+            else {
+                /* line-by-line tracing support */
+                if (PyDTrace_LINE_ENABLED()) {
+                    maybe_dtrace_line(frame, &tstate->trace_info, instr_prev);
+                }
 
-                        stack_pointer = _PyFrame_GetStackPointer(frame);
-                        frame->stacktop = -1;
+                if (cframe.use_tracing &&
+                    tstate->c_tracefunc != NULL && !tstate->tracing) {
+                    int err;
+                    /* see maybe_call_line_trace()
+                    for expository comments */
+                    _PyFrame_SetStackPointer(frame, stack_pointer);
+
+                    err = maybe_call_line_trace(tstate->c_tracefunc,
+                                                tstate->c_traceobj,
+                                                tstate, frame, instr_prev);
+                    if (err) {
+                        /* trace function raised an exception */
+                        next_instr++;
+                        goto error;
                     }
+                    /* Reload possibly changed frame fields */
+                    next_instr = frame->prev_instr;
+
+                    stack_pointer = _PyFrame_GetStackPointer(frame);
+                    frame->stacktop = -1;
+                }
             }
         }
         TRACING_NEXTOPARG();
@@ -6855,13 +6845,8 @@ maybe_call_line_trace(Py_tracefunc func, PyObject *obj,
        then call the trace function if we're tracing source lines.
     */
     initialize_trace_info(&tstate->trace_info, frame);
-    int entry_point = 0;
-    _Py_CODEUNIT *code = _PyCode_CODE(frame->f_code);
-    while (_PyOpcode_Deopt[_Py_OPCODE(code[entry_point])] != RESUME) {
-        entry_point++;
-    }
     int lastline;
-    if (instr_prev <= entry_point) {
+    if (instr_prev <= frame->f_code->_co_firsttraceable) {
         lastline = -1;
     }
     else {

Tools/scripts/deepfreeze.py

@@ -20,6 +20,9 @@
 verbose = False
 identifiers, strings = get_identifiers_and_strings()
 
+# This must be kept in sync with opcode.py
+RESUME = 151
+
 def isprintable(b: bytes) -> bool:
     return all(0x20 <= c < 0x7f for c in b)
 
@@ -267,6 +270,10 @@ def generate_code(self, name: str, code: types.CodeType) -> str:
             self.write(f".co_qualname = {co_qualname},")
             self.write(f".co_linetable = {co_linetable},")
             self.write(f".co_code_adaptive = {co_code_adaptive},")
+            for i, op in enumerate(code.co_code[::2]):
+                if op == RESUME:
+                    self.write(f"._co_firsttraceable = {i},")
+                    break
         name_as_code = f"(PyCodeObject *)&{name}"
         self.deallocs.append(f"_PyStaticCode_Dealloc({name_as_code});")
         self.interns.append(f"_PyStaticCode_InternStrings({name_as_code})")