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gh-104635: Eliminate redundant STORE_FAST instructions in the compiler #105040

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gh-104635: Eliminate redundant STORE_FAST instructions in the compiler #105040

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7b5afb0
Implement simple dead store elimination in cfg opt
corona10 May 28, 2023
2a886ba
Implement POP_TOP__STORE_FAST super instruction
corona10 May 28, 2023
553b361
Only when same line number
corona10 May 28, 2023
0b601dc
remove white space
corona10 May 28, 2023
9039dfe
Implement POP_TOP__POP_TOP
corona10 May 28, 2023
067fc53
Address code review
corona10 May 31, 2023
827fd69
Add NEWS.d
corona10 May 31, 2023
99a2cea
Add test code
corona10 May 31, 2023
69c1aae
fix
corona10 May 31, 2023
c119a6f
Update Misc/NEWS.d/next/Core and Builtins/2023-05-31-16-53-17.gh-issu…
corona10 Jun 1, 2023
6d159bb
Address code review
corona10 Jun 1, 2023
ba46ff3
Address code review
corona10 Jun 1, 2023
b0e0a06
Move apply_static_swap to the last phase of bb optimization
corona10 Jun 1, 2023
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8 changes: 4 additions & 4 deletions Include/internal/pycore_opcode.h
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4 changes: 3 additions & 1 deletion Include/internal/pycore_opcode_utils.h
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,9 @@ extern "C" {
(opcode) == LOAD_FAST__LOAD_CONST || \
(opcode) == LOAD_CONST__LOAD_FAST || \
(opcode) == STORE_FAST__LOAD_FAST || \
(opcode) == STORE_FAST__STORE_FAST)
(opcode) == STORE_FAST__STORE_FAST) || \
(opcode) == POP_TOP__POP_TOP || \
(opcode) == POP_TOP__STORE_FAST


#define LOG_BITS_PER_INT 5
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2 changes: 2 additions & 0 deletions Include/opcode.h
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4 changes: 4 additions & 0 deletions Lib/opcode.py
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Expand Up @@ -435,6 +435,10 @@ def pseudo_op(name, op, real_ops):
"SEND": [
"SEND_GEN",
],
"POP_TOP": [
"POP_TOP__POP_TOP",
"POP_TOP__STORE_FAST"
]
}
_specialized_instructions = [
opcode for family in _specializations.values() for opcode in family
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2 changes: 1 addition & 1 deletion Lib/test/test_dis.py
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Expand Up @@ -811,7 +811,7 @@ def extended_arg_quick():
%3d 2 LOAD_CONST 1 (Ellipsis)
4 EXTENDED_ARG 1
6 UNPACK_EX 256
8 STORE_FAST 0 (_)
8 POP_TOP
10 STORE_FAST 0 (_)
12 RETURN_CONST 0 (None)
"""% (extended_arg_quick.__code__.co_firstlineno,
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52 changes: 51 additions & 1 deletion Lib/test/test_peepholer.py
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Expand Up @@ -1071,7 +1071,57 @@ def test_no_unsafe_static_swap(self):
('POP_TOP', 0, 4),
('RETURN_VALUE', 5)
]
self.cfg_optimization_test(insts, insts, consts=list(range(3)), nlocals=1)
expected_insts = [
('LOAD_CONST', 0, 1),
('LOAD_CONST', 1, 2),
('NOP', 0, 3),
('STORE_FAST', 1, 4),
('POP_TOP', 0, 4),
('RETURN_VALUE', 5)
]
self.cfg_optimization_test(insts, expected_insts, consts=list(range(3)), nlocals=1)

def test_dead_store_elimination_in_same_lineno(self):
insts = [
('LOAD_CONST', 0, 1),
('LOAD_CONST', 1, 2),
('LOAD_CONST', 2, 3),
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 4),
('RETURN_VALUE', 5)
]
expected_insts = [
('LOAD_CONST', 0, 1),
('LOAD_CONST', 1, 2),
('NOP', 0, 3),
('POP_TOP', 0, 4),
Comment on lines +1097 to +1098
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This is a cool benefit I didn't realize we'd also get! LOAD_*/POP_TOP pairs can be eliminated entirely.

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Ideally this would just become LOAD_CONST NOP NOP STORE_FAST though, right?

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@carljm carljm Jun 2, 2023 •
edited
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Yes; I think that's an orthogonal improvement to the LOAD/POP elimination optimization, allowing it to ignore intervening NOP. Or maybe it has to do rather with making it multi-pass? Or both? I haven't checked.

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@corona10 corona10 Jun 3, 2023 •
edited
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Maybe we can run the loop of optimization until there are no opcode changes.
(I didn't test yet)

('STORE_FAST', 1, 4),
('RETURN_VALUE', 5)
]
self.cfg_optimization_test(insts, expected_insts, consts=list(range(3)), nlocals=1)

def test_no_dead_store_elimination_in_different_lineno(self):
insts = [
('LOAD_CONST', 0, 1),
('LOAD_CONST', 1, 2),
('LOAD_CONST', 2, 3),
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 5),
('STORE_FAST', 1, 6),
('RETURN_VALUE', 5)
]
expected_insts = [
('LOAD_CONST', 0, 1),
('LOAD_CONST', 1, 2),
('LOAD_CONST', 2, 3),
('STORE_FAST', 1, 4),
('STORE_FAST', 1, 5),
('STORE_FAST', 1, 6),
('RETURN_VALUE', 5)
]
self.cfg_optimization_test(insts, expected_insts, consts=list(range(3)), nlocals=1)


if __name__ == "__main__":
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2023-05-31-16-53-17.gh-issue-104635.iwf0d8.rst
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@@ -0,0 +1,2 @@
Eliminate redundant :opcode:`STORE_FAST` instructions in the compiler.
Patch by Dong-hee Na and Carl Meyer.
2 changes: 2 additions & 0 deletions Python/bytecodes.c
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Original file line number Diff line number Diff line change
Expand Up @@ -213,6 +213,8 @@ dummy_func(
super(STORE_FAST__LOAD_FAST) = STORE_FAST + LOAD_FAST;
super(STORE_FAST__STORE_FAST) = STORE_FAST + STORE_FAST;
super(LOAD_CONST__LOAD_FAST) = LOAD_CONST + LOAD_FAST;
super(POP_TOP__POP_TOP) = POP_TOP + POP_TOP;
super(POP_TOP__STORE_FAST) = POP_TOP + STORE_FAST;

inst(POP_TOP, (value --)) {
DECREF_INPUTS();
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22 changes: 17 additions & 5 deletions Python/flowgraph.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1515,15 +1515,18 @@ optimize_basic_block(PyObject *const_cache, basicblock *bb, PyObject *consts)
*/
}
break;
case STORE_FAST:
if (opcode == nextop &&
oparg == bb->b_instr[i+1].i_oparg &&
bb->b_instr[i].i_loc.lineno == bb->b_instr[i+1].i_loc.lineno) {
bb->b_instr[i].i_opcode = POP_TOP;
bb->b_instr[i].i_oparg = 0;
}
break;
case SWAP:
if (oparg == 1) {
INSTR_SET_OP0(inst, NOP);
break;
}
if (swaptimize(bb, &i) < 0) {
goto error;
}
apply_static_swaps(bb, i);
break;
case KW_NAMES:
break;
Expand All @@ -1538,6 +1541,15 @@ optimize_basic_block(PyObject *const_cache, basicblock *bb, PyObject *consts)
assert (!HAS_CONST(inst->i_opcode));
}
}
for (int i = 0; i < bb->b_iused; i++) {
cfg_instr *inst = &bb->b_instr[i];
if (inst->i_opcode == SWAP) {
if (swaptimize(bb, &i) < 0) {
goto error;
}
apply_static_swaps(bb, i);
}
}
return SUCCESS;
error:
return ERROR;
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