localrepo: also fastpath access to working copy parents when possible
If the filter level guarantee that the working copy parents will be visible, we
allow fast path access to them. With this change multiple commands can now run
without triggering filtering.
After using the quick access mechanism introduced, the whole series results in
pretty good performance gain:
```
All benchmarks:
before after ratio
[8e095512] [36b2f659]
- 711±0.8ms 60.7±0.2ms 0.09 simple_command.read.diff.empty.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 1) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 712±0.8ms 61.6±0.2ms 0.09 simple_command.read.diff.empty.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 1) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 690±1ms 93.5±0.3ms 0.14 simple_command.read.diff.empty.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 1) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 688±1ms 93.8±0.3ms 0.14 simple_command.read.diff.empty.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 1) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 714±1ms 60.7±0.8ms 0.09 simple_command.read.diff.empty.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 2) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 713±1ms 60.9±0.3ms 0.09 simple_command.read.diff.empty.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 2) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 689±1ms 93.7±0.2ms 0.14 simple_command.read.diff.empty.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 2) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 687±2ms 92.8±0.2ms 0.14 simple_command.read.diff.empty.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 2) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 799±2ms 98.1±0.6ms 0.12 simple_command.read.export.bare.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 800±0.8ms 100.0±0.4ms 0.12 simple_command.read.export.bare.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 711±0.9ms 111±0.2ms 0.16 simple_command.read.export.bare.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 711±1ms 112±0.3ms 0.16 simple_command.read.export.bare.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 760±1ms 59.8±0.1ms 0.08 simple_command.read.status.wc_clean.default.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 1) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 763±2ms 62.2±0.3ms 0.08 simple_command.read.status.wc_clean.default.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 1) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 689±1ms 93.1±0.3ms 0.14 simple_command.read.status.wc_clean.default.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 1) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 688±1ms 94.3±0.3ms 0.14 simple_command.read.status.wc_clean.default.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 1) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 763±1ms 60.1±0.2ms 0.08 simple_command.read.status.wc_clean.default.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 2) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 763±1ms 62.1±0.4ms 0.08 simple_command.read.status.wc_clean.default.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 2) [citrea/virtualenv-py2.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
- 689±0.8ms 93.2±0.2ms 0.14 simple_command.read.status.wc_clean.default.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 2) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYc-HGWITHRUSTEXTcpython]
- 687±0.9ms 94.1±0.3ms 0.14 simple_command.read.status.wc_clean.default.time_bench('mercurial-filtered-2019-11-22', 'zstd', 'default', True, True, True, True, True, 2) [citrea/virtualenv-py3.7-pyyaml-HGMODULEPOLICYrust+c-HGWITHRUSTEXTcpython]
```
Differential Revision:
https://phab.mercurial-scm.org/D7492
