GH-128685: Specialize (rather than quicken) LOAD_CONST into LOAD_CONST_[IM]MORTAL - #128708
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brandtbucher
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Looks good, just a couple of thoughts.
Also, any perf numbers? I doubt it would be too significant, but this is a very perf-sensitive instruction/optimization.
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| Python 3.14a4 3610 (Add VALUE_WITH_FAKE_GLOBALS format to annotationlib) | ||
| Python 3.14a4 3611 (Add NOT_TAKEN instruction) | ||
| Python 3.14a4 3612 (Add POP_ITER and INSTRUMENTED_POP_ITER) | ||
| Python 3.14a4 3613 (Add LOAD_CONST_MORTAL instruction) |
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This is a specialization, right? So we shouldn't need a magic bump (since the specialized variants don't occur in marshalled data).
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Adding the extra instruction changes the allocated numbers for other instructions.
Even if it isn't absolutely necessary, it is harmless.
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| inst(LOAD_CONST, (-- value)) { | ||
| /* We can't do this in the bytecode compiler as | ||
| * marshalling can intern strings and make them immortal. */ | ||
| PyObject *obj = GETITEM(FRAME_CO_CONSTS, oparg); | ||
| value = PyStackRef_FromPyObjectNew(obj); | ||
| #if ENABLE_SPECIALIZATION | ||
| if (this_instr->op.code == LOAD_CONST) { | ||
| this_instr->op.code = _Py_IsImmortal(obj) ? LOAD_CONST_IMMORTAL : LOAD_CONST_MORTAL; | ||
| } | ||
| #endif | ||
| } |
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Why the check for this_instr->op.code == LOAD_CONST?
Also, minor, but maybe a bit more idiomatic with the rest of the bytecode definitions to split the specializing part out and reuse the code for loading the const? I think this would also make LOAD_CONST a viable tier two instruction (which it currently isn't). Though actually tracing through one should be rare, I can think of cases where it might happen.
| inst(LOAD_CONST, (-- value)) { | |
| /* We can't do this in the bytecode compiler as | |
| * marshalling can intern strings and make them immortal. */ | |
| PyObject *obj = GETITEM(FRAME_CO_CONSTS, oparg); | |
| value = PyStackRef_FromPyObjectNew(obj); | |
| #if ENABLE_SPECIALIZATION | |
| if (this_instr->op.code == LOAD_CONST) { | |
| this_instr->op.code = _Py_IsImmortal(obj) ? LOAD_CONST_IMMORTAL : LOAD_CONST_MORTAL; | |
| } | |
| #endif | |
| } | |
| specializing op(_SPECIALIZE_LOAD_CONST, (--)) { | |
| /* We can't do this in the bytecode compiler as | |
| * marshalling can intern strings and make them immortal. */ | |
| #if ENABLE_SPECIALIZATION | |
| this_instr->op.code = _Py_IsImmortal(obj) ? LOAD_CONST_IMMORTAL : LOAD_CONST_MORTAL; | |
| #endif | |
| } | |
| macro(LOAD_CONST) = _SPECIALIZE_LOAD_CONST + LOAD_CONST_MORTAL; |
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Why the check for this_instr->op.code == LOAD_CONST?
Instrumentation. The opcode might be INSTRUMENTED_LINE for example.
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split the specializing part out
The specializing part needs to load the value to test it, so separating out the specialization just duplicates that.
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This was previously handled by `_PyCode_Quicken`, but moved to specialization in pythongh-128708. Enable it for the free-threaded build.
This was previously handled by `_PyCode_Quicken`, but moved to specialization in pythongh-128708. Enable it for the free-threaded build.
This PR changes LOAD_CONST to specialize into either LOAD_CONST or LOAD_CONST_IMMORTAL.
This ensures that LOAD_CONST for immortals returns to LOAD_CONST_IMMORTAL after instrumentation.
This is unlikely to make any observable difference, but we generally expect instructions to return to their specialized forms after instrumentation is removed and LOAD_CONST is a very common instruction, so is likely to get instrumented.
Skipping news as this should have no observable effect.