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gh-106581: Split CALL_BOUND_METHOD_EXACT_ARGS into uops#108462

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Merged
gvanrossum merged 1 commit into from
Aug 25, 2023
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gh-106581: Split CALL_BOUND_METHOD_EXACT_ARGS into uops #108462

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41 changes: 27 additions & 14 deletions Include/internal/pycore_opcode_metadata.h
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10 changes: 10 additions & 0 deletions Python/abstract_interp_cases.c.h
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29 changes: 20 additions & 9 deletions Python/bytecodes.c
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Original file line numberDiff line numberDiff line change
Expand Up@@ -2940,19 +2940,18 @@ dummy_func(
CHECK_EVAL_BREAKER();
}

// Start out with [NULL, bound_method, arg1, arg2, ...]
// Transform to [callable, self, arg1, arg2, ...]
// Then fall through to CALL_PY_EXACT_ARGS
inst(CALL_BOUND_METHOD_EXACT_ARGS, (unused/1, unused/2, callable, null, unused[oparg] -- unused)) {
op(_CHECK_CALL_BOUND_METHOD_EXACT_ARGS, (callable, null, unused[oparg] -- callable, null, unused[oparg])) {
DEOPT_IF(null != NULL, CALL);
DEOPT_IF(Py_TYPE(callable) != &PyMethod_Type, CALL);
}

op(_INIT_CALL_BOUND_METHOD_EXACT_ARGS, (callable, unused, unused[oparg] -- func, self, unused[oparg])) {
STAT_INC(CALL, hit);
PyObject *self = ((PyMethodObject *)callable)->im_self;
PEEK(oparg + 1) = Py_NewRef(self); // self_or_null
PyObject *meth = ((PyMethodObject *)callable)->im_func;
PEEK(oparg + 2) = Py_NewRef(meth); // callable
self = Py_NewRef(((PyMethodObject *)callable)->im_self);
stack_pointer[-1 - oparg] = self; // Patch stack as it is used by _INIT_CALL_PY_EXACT_ARGS
func = Py_NewRef(((PyMethodObject *)callable)->im_func);
stack_pointer[-2 - oparg] = func; // This is used by CALL, upon deoptimization
Comment on lines +2951 to +2953

@carljmcarljmAug 24, 2023

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Hmm, so these lines appear to be entirely redundant for the uops executor, as the stack-effect output of func, self, ... causes the exact same assignments to be emitted automatically right after these lines.

But this is needed for the bytecode interpreter. Since in that case all the uops are squashed together and their inputs and outputs are chained together as local variables, but we really need to update the actual stack here, for the reasons mentioned in the comments.

I don't know how often such uop stack-patching cases will occur (from what I can find, this is the first one?). If there will be more, it might be nice to have syntax to mark an output in the stack-effects definition of the uop as "must actually modify the stack", and then have the cases generator automatically emit this (and the executor cases wouldn't have the duplicate assignments.)

@gvanrossumgvanrossumAug 25, 2023

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Thanks for the review!

It looks to be pretty uncommon -- calls are special in many ways. Agreed that if this proliferates we should teach the code generator to do this. It also looks like a C compiler would have a hard time optimizing the duplication in Tier 2 away, because there's an intervening Py_DECREF(). If that becomes an issue but it remains limited to just this case we could surround the flushes with #ifdef TIER_ONE / #endif.

I'll merge this and see what's next on the agenda. (I suspect either KW_NAMES or splitting LOAD_ATTR specializations.)

Py_DECREF(callable);
GO_TO_INSTRUCTION(CALL_PY_EXACT_ARGS);
}

op(_CHECK_PEP_523, (--)) {
Expand DownExpand Up@@ -3010,6 +3009,18 @@ dummy_func(
#endif
}

macro(CALL_BOUND_METHOD_EXACT_ARGS) =
unused/1 + // Skip over the counter
_CHECK_PEP_523 +
_CHECK_CALL_BOUND_METHOD_EXACT_ARGS +
_INIT_CALL_BOUND_METHOD_EXACT_ARGS +
_CHECK_FUNCTION_EXACT_ARGS +
_CHECK_STACK_SPACE +
_INIT_CALL_PY_EXACT_ARGS +
SAVE_IP + // Tier 2 only; special-cased oparg
SAVE_CURRENT_IP + // Sets frame->prev_instr
_PUSH_FRAME;

macro(CALL_PY_EXACT_ARGS) =
unused/1 + // Skip over the counter
_CHECK_PEP_523 +
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26 changes: 26 additions & 0 deletions Python/executor_cases.c.h
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98 changes: 87 additions & 11 deletions Python/generated_cases.c.h
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2 changes: 1 addition & 1 deletion Tools/cases_generator/generate_cases.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -444,7 +444,7 @@ def write_metadata(self, metadata_filename: str, pymetadata_filename: str) -> No
with self.out.block("struct opcode_macro_expansion", ";"):
self.out.emit("int nuops;")
self.out.emit(
"struct { int16_t uop; int8_t size; int8_t offset; } uops[8];"
"struct { int16_t uop; int8_t size; int8_t offset; } uops[12];"
)
self.out.emit("")

Expand Down