Don't write to locals if they are never read

[tekknolagi]

This is common in code like:

for _ in range(10):
    pass

[github-actions]

{
  "django_minimal_requests": {
    "benchmark": "django_minimal_requests",
    "cg_instructions before": 682020,
    "cg_instructions now": 681925,
    "cg_instructions ∆": "-0.0%",
    "interpreter_args": [],
    "interpreter_name": "pyro",
    "version before": "08f3f441eef002602de86641c443287e0b994711",
    "version now": "258d2f440c6c58686b305463a70a0c9b625ee286"
  }
}

[github-actions]

Summary

Metric	Average	Best	Worst	Notes
cg_instructions	0.1%	bench_pickle -0.0%	bench_compile 0.8%	typically < 0.2% noise

Benchmark details

Base vs. New

benchmark	cg_instructions
2to3	0.0%
bench_base64	0.0%
bench_compile	0.8%
bench_pickle	-0.0%
deltablue	0.0%
fannkuch	0.0%
go	0.0%
loadproperty	0.0%
nbody	0.0%
nqueens	0.0%
pyflate	0.0%
pystone	0.0%
richards	-0.0%

CPython vs New

benchmark	cg_instructions
2to3	-10.8%
bench_base64	-40.2%
bench_compile	1084.5%
bench_pickle	-27.9%
deltablue	-65.2%
fannkuch	-3.5%
go	-64.6%
loadproperty	-75.6%
nbody	20.7%
nqueens	25.5%
pyflate	-33.8%
pystone	-73.9%
richards	-80.1%

Base

benchmark	cg_instructions
2to3	2,287,410,091
bench_base64	2,882,265,264
bench_compile	2,905,298,742
bench_pickle	2,985,921,079
deltablue	1,430,181,702
fannkuch	5,397,319,728
go	1,864,219,894
loadproperty	427,273,989
nbody	9,408,436,235
nqueens	2,776,551,355
pyflate	9,583,535,272
pystone	1,038,534,388
richards	957,217,422

New

benchmark	cg_instructions
2to3	2,287,440,943
bench_base64	2,882,292,665
bench_compile	2,929,013,664
bench_pickle	2,985,799,872
deltablue	1,430,193,210
fannkuch	5,397,331,793
go	1,864,257,697
loadproperty	427,281,972
nbody	9,408,441,785
nqueens	2,776,557,678
pyflate	9,583,538,906
pystone	1,038,538,054
richards	957,217,161

CPython

benchmark	cg_instructions
2to3	2,563,596,659
bench_base64	4,820,239,484
bench_compile	247,275,016
bench_pickle	4,143,888,325
deltablue	4,109,337,945
fannkuch	5,594,144,646
go	5,267,461,726
loadproperty	1,747,769,948
nbody	7,793,857,367
nqueens	2,213,172,338
pyflate	14,468,018,995
pystone	3,981,578,803
richards	4,821,556,013