GH-93516: Speedup line number checks when tracing. (GH-93763)

* Use a lookup table to reduce overhead of getting line numbers during tracing.

Author: markshannon

Include/cpython/code.h

@@ -62,7 +62,8 @@ typedef uint16_t _Py_CODEUNIT;
     PyObject *co_exceptiontable;   /* Byte string encoding exception handling  \
                                       table */                                 \
     int co_flags;                  /* CO_..., see below */                     \
-    int co_warmup;                 /* Warmup counter for quickening */         \
+    short co_warmup;                 /* Warmup counter for quickening */       \
+    short _co_linearray_entry_size;  /* Size of each entry in _co_linearray */ \
                                                                                \
     /* The rest are not so impactful on performance. */                        \
     int co_argcount;              /* #arguments, except *args */               \
@@ -90,6 +91,7 @@ typedef uint16_t _Py_CODEUNIT;
     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 */   \
+    char *_co_linearray;          /* array of line offsets */                  \
     /* 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. */                                \

Include/internal/pycore_code.h

@@ -461,6 +461,35 @@ adaptive_counter_backoff(uint16_t counter) {
 }
 
 
+/* Line array cache for tracing */
+
+extern int _PyCode_CreateLineArray(PyCodeObject *co);
+
+static inline int
+_PyCode_InitLineArray(PyCodeObject *co)
+{
+    if (co->_co_linearray) {
+        return 0;
+    }
+    return _PyCode_CreateLineArray(co);
+}
+
+static inline int
+_PyCode_LineNumberFromArray(PyCodeObject *co, int index)
+{
+    assert(co->_co_linearray != NULL);
+    assert(index >= 0);
+    assert(index < Py_SIZE(co));
+    if (co->_co_linearray_entry_size == 2) {
+        return ((int16_t *)co->_co_linearray)[index];
+    }
+    else {
+        assert(co->_co_linearray_entry_size == 4);
+        return ((int32_t *)co->_co_linearray)[index];
+    }
+}
+
+
 #ifdef __cplusplus
 }
 #endif

Misc/NEWS.d/next/Core and Builtins/2022-06-13-10-48-09.gh-issue-93516.yJSait.rst

@@ -0,0 +1,2 @@
+Lazily create a table mapping bytecode offsets to line numbers to speed up
+calculation of line numbers when tracing.

Objects/codeobject.c

@@ -339,6 +339,8 @@ init_code(PyCodeObject *co, struct _PyCodeConstructor *con)
     co->_co_code = NULL;
 
     co->co_warmup = QUICKENING_INITIAL_WARMUP_VALUE;
+    co->_co_linearray_entry_size = 0;
+    co->_co_linearray = NULL;
     memcpy(_PyCode_CODE(co), PyBytes_AS_STRING(con->code),
            PyBytes_GET_SIZE(con->code));
     int entry_point = 0;
@@ -703,13 +705,60 @@ PyCode_NewEmpty(const char *filename, const char *funcname, int firstlineno)
    lnotab_notes.txt for the details of the lnotab representation.
 */
 
+int
+_PyCode_CreateLineArray(PyCodeObject *co)
+{
+    assert(co->_co_linearray == NULL);
+    PyCodeAddressRange bounds;
+    int size;
+    int max_line = 0;
+    _PyCode_InitAddressRange(co, &bounds);
+    while(_PyLineTable_NextAddressRange(&bounds)) {
+        if (bounds.ar_line > max_line) {
+            max_line = bounds.ar_line;
+        }
+    }
+    if (max_line < (1 << 15)) {
+        size = 2;
+    }
+    else {
+        size = 4;
+    }
+    co->_co_linearray = PyMem_Malloc(Py_SIZE(co)*size);
+    if (co->_co_linearray == NULL) {
+        PyErr_NoMemory();
+        return -1;
+    }
+    co->_co_linearray_entry_size = size;
+    _PyCode_InitAddressRange(co, &bounds);
+    while(_PyLineTable_NextAddressRange(&bounds)) {
+        int start = bounds.ar_start / sizeof(_Py_CODEUNIT);
+        int end = bounds.ar_end / sizeof(_Py_CODEUNIT);
+        for (int index = start; index < end; index++) {
+            assert(index < (int)Py_SIZE(co));
+            if (size == 2) {
+                assert(((int16_t)bounds.ar_line) == bounds.ar_line);
+                ((int16_t *)co->_co_linearray)[index] = bounds.ar_line;
+            }
+            else {
+                assert(size == 4);
+                ((int32_t *)co->_co_linearray)[index] = bounds.ar_line;
+            }
+        }
+    }
+    return 0;
+}
+
 int
 PyCode_Addr2Line(PyCodeObject *co, int addrq)
 {
     if (addrq < 0) {
         return co->co_firstlineno;
     }
     assert(addrq >= 0 && addrq < _PyCode_NBYTES(co));
+    if (co->_co_linearray) {
+        return _PyCode_LineNumberFromArray(co, addrq / sizeof(_Py_CODEUNIT));
+    }
     PyCodeAddressRange bounds;
     _PyCode_InitAddressRange(co, &bounds);
     return _PyCode_CheckLineNumber(addrq, &bounds);
@@ -1549,6 +1598,9 @@ code_dealloc(PyCodeObject *co)
     if (co->co_weakreflist != NULL) {
         PyObject_ClearWeakRefs((PyObject*)co);
     }
+    if (co->_co_linearray) {
+        PyMem_Free(co->_co_linearray);
+    }
     if (co->co_warmup == 0) {
         _Py_QuickenedCount--;
     }
@@ -2106,6 +2158,10 @@ _PyStaticCode_Dealloc(PyCodeObject *co)
         PyObject_ClearWeakRefs((PyObject *)co);
         co->co_weakreflist = NULL;
     }
+    if (co->_co_linearray) {
+        PyMem_Free(co->_co_linearray);
+        co->_co_linearray = NULL;
+    }
 }
 
 int

Python/ceval.c

@@ -6799,9 +6799,10 @@ call_trace(Py_tracefunc func, PyObject *obj,
     tstate->tracing_what = what;
     PyThreadState_EnterTracing(tstate);
     assert(_PyInterpreterFrame_LASTI(frame) >= 0);
-    initialize_trace_info(&tstate->trace_info, frame);
-    int addr = _PyInterpreterFrame_LASTI(frame) * sizeof(_Py_CODEUNIT);
-    f->f_lineno = _PyCode_CheckLineNumber(addr, &tstate->trace_info.bounds);
+    if (_PyCode_InitLineArray(frame->f_code)) {
+        return -1;
+    }
+    f->f_lineno = _PyCode_LineNumberFromArray(frame->f_code, _PyInterpreterFrame_LASTI(frame));
     result = func(obj, f, what, arg);
     f->f_lineno = 0;
     PyThreadState_LeaveTracing(tstate);
@@ -6838,16 +6839,17 @@ maybe_call_line_trace(Py_tracefunc func, PyObject *obj,
        represents a jump backwards, update the frame's line number and
        then call the trace function if we're tracing source lines.
     */
-    initialize_trace_info(&tstate->trace_info, frame);
+    if (_PyCode_InitLineArray(frame->f_code)) {
+        return -1;
+    }
     int lastline;
     if (instr_prev <= frame->f_code->_co_firsttraceable) {
         lastline = -1;
     }
     else {
-        lastline = _PyCode_CheckLineNumber(instr_prev*sizeof(_Py_CODEUNIT), &tstate->trace_info.bounds);
+        lastline = _PyCode_LineNumberFromArray(frame->f_code, instr_prev);
     }
-    int addr = _PyInterpreterFrame_LASTI(frame) * sizeof(_Py_CODEUNIT);
-    int line = _PyCode_CheckLineNumber(addr, &tstate->trace_info.bounds);
+    int line = _PyCode_LineNumberFromArray(frame->f_code, _PyInterpreterFrame_LASTI(frame));
     PyFrameObject *f = _PyFrame_GetFrameObject(frame);
     if (f == NULL) {
         return -1;

Tools/scripts/deepfreeze.py

@@ -254,6 +254,7 @@ def generate_code(self, name: str, code: types.CodeType) -> str:
             self.write(f".co_exceptiontable = {co_exceptiontable},")
             self.field(code, "co_flags")
             self.write(".co_warmup = QUICKENING_INITIAL_WARMUP_VALUE,")
+            self.write("._co_linearray_entry_size = 0,")
             self.field(code, "co_argcount")
             self.field(code, "co_posonlyargcount")
             self.field(code, "co_kwonlyargcount")
@@ -271,6 +272,7 @@ def generate_code(self, name: str, code: types.CodeType) -> str:
             self.write(f".co_name = {co_name},")
             self.write(f".co_qualname = {co_qualname},")
             self.write(f".co_linetable = {co_linetable},")
+            self.write("._co_linearray = NULL,")
             self.write(f".co_code_adaptive = {co_code_adaptive},")
             for i, op in enumerate(code.co_code[::2]):
                 if op == RESUME: