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Commit 10a9e781 authored by Jeremy Hylton's avatar Jeremy Hylton
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Refactor: Move code that uses co_lnotab from ceval to codeobject

parent 9c31ff03
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Showing with 162 additions and 117 deletions
Include/code.h
View file @ 10a9e781
......@@ -72,6 +72,21 @@ PyAPI_FUNC(int) PyCode_Addr2Line(PyCodeObject *, int);
((*(co)->co_code->ob_type->tp_as_buffer->bf_getreadbuffer) \
((co)->co_code, 0, (void **)(pp)))
typedef struct _addr_pair {
int ap_lower;
int ap_upper;
} PyAddrPair;
/* Check whether lasti (an instruction offset) falls outside bounds
and whether it is a line number that should be traced. Returns
a line number if it should be traced or -1 if the line should not.
If lasti is not within bounds, updates bounds.
*/
PyAPI_FUNC(int) PyCode_CheckLineNumber(PyCodeObject* co,
int lasti, PyAddrPair *bounds);
#ifdef __cplusplus
}
#endif
......
Objects/codeobject.c
View file @ 10a9e781
......@@ -451,3 +451,136 @@ PyCode_Addr2Line(PyCodeObject *co, int addrq)
}
return line;
}
/*
Check whether the current instruction is at the start of a line.
*/
/* The theory of SET_LINENO-less tracing.
In a nutshell, we use the co_lnotab field of the code object
to tell when execution has moved onto a different line.
As mentioned above, the basic idea is so set things up so
that
*instr_lb <= frame->f_lasti < *instr_ub
is true so long as execution does not change lines.
This is all fairly simple. Digging the information out of
co_lnotab takes some work, but is conceptually clear.
Somewhat harder to explain is why we don't *always* call the
line trace function when the above test fails.
Consider this code:
1: def f(a):
2: if a:
3: print 1
4: else:
5: print 2
which compiles to this:
2 0 LOAD_FAST 0 (a)
3 JUMP_IF_FALSE 9 (to 15)
6 POP_TOP
3 7 LOAD_CONST 1 (1)
10 PRINT_ITEM
11 PRINT_NEWLINE
12 JUMP_FORWARD 6 (to 21)
>> 15 POP_TOP
5 16 LOAD_CONST 2 (2)
19 PRINT_ITEM
20 PRINT_NEWLINE
>> 21 LOAD_CONST 0 (None)
24 RETURN_VALUE
If 'a' is false, execution will jump to instruction at offset
15 and the co_lnotab will claim that execution has moved to
line 3. This is at best misleading. In this case we could
associate the POP_TOP with line 4, but that doesn't make
sense in all cases (I think).
What we do is only call the line trace function if the co_lnotab
indicates we have jumped to the *start* of a line, i.e. if the
current instruction offset matches the offset given for the
start of a line by the co_lnotab.
This also takes care of the situation where 'a' is true.
Execution will jump from instruction offset 12 to offset 21.
Then the co_lnotab would imply that execution has moved to line
5, which is again misleading.
Why do we set f_lineno when tracing? Well, consider the code
above when 'a' is true. If stepping through this with 'n' in
pdb, you would stop at line 1 with a "call" type event, then
line events on lines 2 and 3, then a "return" type event -- but
you would be shown line 5 during this event. This is a change
from the behaviour in 2.2 and before, and I've found it
confusing in practice. By setting and using f_lineno when
tracing, one can report a line number different from that
suggested by f_lasti on this one occasion where it's desirable.
*/
int
PyCode_CheckLineNumber(PyCodeObject* co, int lasti, PyAddrPair *bounds)
{
int size, addr, line;
unsigned char* p;
p = (unsigned char*)PyString_AS_STRING(co->co_lnotab);
size = PyString_GET_SIZE(co->co_lnotab) / 2;
addr = 0;
line = co->co_firstlineno;
assert(line > 0);
/* possible optimization: if f->f_lasti == instr_ub
(likely to be a common case) then we already know
instr_lb -- if we stored the matching value of p
somwhere we could skip the first while loop. */
/* see comments in compile.c for the description of
co_lnotab. A point to remember: increments to p
should come in pairs -- although we don't care about
the line increments here, treating them as byte
increments gets confusing, to say the least. */
while (size > 0) {
if (addr + *p > lasti)
break;
addr += *p++;
if (*p)
bounds->ap_lower = addr;
line += *p++;
--size;
}
/* If lasti and addr don't match exactly, we don't want to
change the lineno slot on the frame or execute a trace
function. Return -1 instead.
*/
if (addr != lasti)
line = -1;
if (size > 0) {
while (--size >= 0) {
addr += *p++;
if (*p++)
break;
}
bounds->ap_upper = addr;
}
else {
bounds->ap_upper = INT_MAX;
}
return line;
}
Python/ceval.c
View file @ 10a9e781
......@@ -3219,132 +3219,29 @@ maybe_call_line_trace(Py_tracefunc func, PyObject *obj,
PyFrameObject *frame, int *instr_lb, int *instr_ub,
int *instr_prev)
{
/* The theory of SET_LINENO-less tracing.
In a nutshell, we use the co_lnotab field of the code object
to tell when execution has moved onto a different line.
As mentioned above, the basic idea is so set things up so
that
*instr_lb <= frame->f_lasti < *instr_ub
is true so long as execution does not change lines.
This is all fairly simple. Digging the information out of
co_lnotab takes some work, but is conceptually clear.
Somewhat harder to explain is why we don't *always* call the
line trace function when the above test fails.
Consider this code:
1: def f(a):
2: if a:
3: print 1
4: else:
5: print 2
which compiles to this:
2 0 LOAD_FAST 0 (a)
3 JUMP_IF_FALSE 9 (to 15)
6 POP_TOP
3 7 LOAD_CONST 1 (1)
10 PRINT_ITEM
11 PRINT_NEWLINE
12 JUMP_FORWARD 6 (to 21)
>> 15 POP_TOP
5 16 LOAD_CONST 2 (2)
19 PRINT_ITEM
20 PRINT_NEWLINE
>> 21 LOAD_CONST 0 (None)
24 RETURN_VALUE
If 'a' is false, execution will jump to instruction at offset
15 and the co_lnotab will claim that execution has moved to
line 3. This is at best misleading. In this case we could
associate the POP_TOP with line 4, but that doesn't make
sense in all cases (I think).
What we do is only call the line trace function if the co_lnotab
indicates we have jumped to the *start* of a line, i.e. if the
current instruction offset matches the offset given for the
start of a line by the co_lnotab.
This also takes care of the situation where 'a' is true.
Execution will jump from instruction offset 12 to offset 21.
Then the co_lnotab would imply that execution has moved to line
5, which is again misleading.
Why do we set f_lineno when tracing? Well, consider the code
above when 'a' is true. If stepping through this with 'n' in
pdb, you would stop at line 1 with a "call" type event, then
line events on lines 2 and 3, then a "return" type event -- but
you would be shown line 5 during this event. This is a change
from the behaviour in 2.2 and before, and I've found it
confusing in practice. By setting and using f_lineno when
tracing, one can report a line number different from that
suggested by f_lasti on this one occasion where it's desirable.
*/
int result = 0;
/* If the last instruction executed isn't in the current
instruction window, reset the window. If the last
instruction happens to fall at the start of a line or if it
represents a jump backwards, call the trace function.
*/
if ((frame->f_lasti < *instr_lb || frame->f_lasti >= *instr_ub)) {
PyCodeObject* co = frame->f_code;
int size, addr, line;
unsigned char* p;
size = PyString_GET_SIZE(co->co_lnotab) / 2;
p = (unsigned char*)PyString_AS_STRING(co->co_lnotab);
addr = 0;
line = co->co_firstlineno;
/* possible optimization: if f->f_lasti == instr_ub
(likely to be a common case) then we already know
instr_lb -- if we stored the matching value of p
somwhere we could skip the first while loop. */
/* see comments in compile.c for the description of
co_lnotab. A point to remember: increments to p
should come in pairs -- although we don't care about
the line increments here, treating them as byte
increments gets confusing, to say the least. */
while (size > 0) {
if (addr + *p > frame->f_lasti)
break;
addr += *p++;
if (*p) *instr_lb = addr;
line += *p++;
--size;
}
int line;
PyAddrPair bounds;
if (addr == frame->f_lasti) {
line = PyCode_CheckLineNumber(frame->f_code, frame->f_lasti,
&bounds);
if (line >= 0) {
frame->f_lineno = line;
result = call_trace(func, obj, frame,
PyTrace_LINE, Py_None);
}
if (size > 0) {
while (--size >= 0) {
addr += *p++;
if (*p++)
break;
}
*instr_ub = addr;
}
else {
*instr_ub = INT_MAX;
}
}
*instr_lb = bounds.ap_lower;
*instr_ub = bounds.ap_upper;
}
else if (frame->f_lasti <= *instr_prev) {
/* jumping back in the same line forces a trace event */
result = call_trace(func, obj, frame,
PyTrace_LINE, Py_None);
result = call_trace(func, obj, frame, PyTrace_LINE, Py_None);
}
*instr_prev = frame->f_lasti;
return result;
......
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