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bpo-43760: Streamline dispatch sequence for machines without computed gotos. #25244

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Merged
merged 3 commits into from
Apr 8, 2021
Merged

bpo-43760: Streamline dispatch sequence for machines without computed gotos. #25244

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82d2cd0
Streamline dispatch sequence for machines without computed gotos.
markshannon Mar 26, 2021
860ca09
Restore stack_pointer before jumping to error handling, in case trace…
markshannon Apr 7, 2021
99a0871
Clarifications suggested by GvR and R Hettinger.
markshannon Apr 8, 2021
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113 changes: 52 additions & 61 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1264,6 +1264,23 @@ eval_frame_handle_pending(PyThreadState *tstate)
-fno-crossjumping).
*/

/* Use macros rather than inline functions, to make it as clear as possible
* to the C compiler that the tracing check is a simple test then branch.
* We want to be sure that the compiler knows this before it generates
* the CFG.
*/
#ifdef LLTRACE
#define OR_LLTRACE || lltrace
#else
#define OR_LLTRACE
#endif

#ifdef WITH_DTRACE
#define OR_DTRACE_LINE || PyDTrace_LINE_ENABLED()
#else
#define OR_DTRACE_LINE
#endif

#ifdef DYNAMIC_EXECUTION_PROFILE
#undef USE_COMPUTED_GOTOS
#define USE_COMPUTED_GOTOS 0
Expand All @@ -1282,37 +1299,22 @@ eval_frame_handle_pending(PyThreadState *tstate)
#endif

#if USE_COMPUTED_GOTOS
#define TARGET(op) \
op: \
TARGET_##op

#ifdef LLTRACE
#define DISPATCH() \
{ \
if (!lltrace && !_Py_TracingPossible(ceval2) && !PyDTrace_LINE_ENABLED()) { \
f->f_lasti = INSTR_OFFSET(); \
NEXTOPARG(); \
goto *opcode_targets[opcode]; \
} \
goto fast_next_opcode; \
}
#define TARGET(op) op: TARGET_##op
#define DISPATCH_GOTO() goto *opcode_targets[opcode]
#else
#define TARGET(op) op
#define DISPATCH_GOTO() goto dispatch_opcode
#endif

#define DISPATCH() \
{ \
if (!_Py_TracingPossible(ceval2) && !PyDTrace_LINE_ENABLED()) { \
f->f_lasti = INSTR_OFFSET(); \
NEXTOPARG(); \
goto *opcode_targets[opcode]; \
if (_Py_TracingPossible(ceval2) OR_DTRACE_LINE OR_LLTRACE) { \
goto tracing_dispatch; \
} \
goto fast_next_opcode; \
f->f_lasti = INSTR_OFFSET(); \
NEXTOPARG(); \
DISPATCH_GOTO(); \
}
#endif

#else
#define TARGET(op) op
#define DISPATCH() goto fast_next_opcode

#endif

#define CHECK_EVAL_BREAKER() \
if (_Py_atomic_load_relaxed(eval_breaker)) { \
Expand Down Expand Up @@ -1598,14 +1600,6 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
_Py_atomic_int * const eval_breaker = &ceval2->eval_breaker;
PyCodeObject *co;

/* when tracing we set things up so that

not (instr_lb <= current_bytecode_offset < instr_ub)

is true when the line being executed has changed. The
initial values are such as to make this false the first
time it is tested. */

const _Py_CODEUNIT *first_instr;
PyObject *names;
PyObject *consts;
Expand All @@ -1620,7 +1614,7 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
}

PyTraceInfo trace_info;
/* Mark trace_info as initialized */
/* Mark trace_info as uninitialized */
trace_info.code = NULL;

/* push frame */
Expand Down Expand Up @@ -1754,10 +1748,10 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)

if (_Py_atomic_load_relaxed(eval_breaker)) {
opcode = _Py_OPCODE(*next_instr);
if (opcode == SETUP_FINALLY ||
opcode == SETUP_WITH ||
opcode == BEFORE_ASYNC_WITH ||
opcode == YIELD_FROM) {
if (opcode != SETUP_FINALLY &&
opcode != SETUP_WITH &&
opcode != BEFORE_ASYNC_WITH &&
opcode != YIELD_FROM) {
/* Few cases where we skip running signal handlers and other
pending calls:
- If we're about to enter the 'with:'. It will prevent
Expand All @@ -1774,16 +1768,15 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
running the signal handler and raising KeyboardInterrupt
(see bpo-30039).
*/
goto fast_next_opcode;
}

if (eval_frame_handle_pending(tstate) != 0) {
goto error;
}
if (eval_frame_handle_pending(tstate) != 0) {
goto error;
}
}
}

fast_next_opcode:
tracing_dispatch:
f->f_lasti = INSTR_OFFSET();
NEXTOPARG();

if (PyDTrace_LINE_ENABLED())
maybe_dtrace_line(f, &trace_info);
Expand All @@ -1805,23 +1798,13 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
JUMPTO(f->f_lasti);
stack_pointer = f->f_valuestack+f->f_stackdepth;
f->f_stackdepth = -1;
if (err)
if (err) {
/* trace function raised an exception */
goto error;
}
NEXTOPARG();
}

/* Extract opcode and argument */

NEXTOPARG();
dispatch_opcode:
#ifdef DYNAMIC_EXECUTION_PROFILE
#ifdef DXPAIRS
dxpairs[lastopcode][opcode]++;
lastopcode = opcode;
#endif
dxp[opcode]++;
#endif

#ifdef LLTRACE
/* Instruction tracing */

Expand All @@ -1837,11 +1820,20 @@ _PyEval_EvalFrameDefault(PyThreadState *tstate, PyFrameObject *f, int throwflag)
}
#endif

dispatch_opcode:
#ifdef DYNAMIC_EXECUTION_PROFILE
#ifdef DXPAIRS
dxpairs[lastopcode][opcode]++;
lastopcode = opcode;
#endif
dxp[opcode]++;
#endif

switch (opcode) {

/* BEWARE!
It is essential that any operation that fails must goto error
and that all operation that succeed call [FAST_]DISPATCH() ! */
and that all operation that succeed call DISPATCH() ! */

case TARGET(NOP): {
DISPATCH();
Expand Down Expand Up @@ -5427,7 +5419,6 @@ unpack_iterable(PyThreadState *tstate, PyObject *v,
return 0;
}


#ifdef LLTRACE
static int
prtrace(PyThreadState *tstate, PyObject *v, const char *str)
Expand Down