sparse-revlog: add a `index_get_start` function in C We are about to implement a native version of `slicechunktodensity`. For clarity, we introduce the helper functions first. This new function provides an efficient way to retrieve some of the information needed by `slicechunktodensity`.

perf: add --clear-revlog flag to branchmapload Having the changelog index already loaded when loading the branchmap can have a large impact on performance. Example runs (large private repository): hg perfbranchmapload -f base ! wall 0.116722 comb 0.120000 user 0.110000 sys 0.010000 (best of 59) hg perfbranchmapload -f base --clear-revlogs ! wall 0.258246 comb 0.230000 user 0.220000 sys 0.010000 (best of 31)

perf: introduce a function to fully "unload" a changelog The function remove various attributes and caches related to changelog. This is getting a common requirement.

perf: use an explicit function in perfbranchmapload This make things clearer.

perf: update function name to match `perfbranchmapload` command Having function with the same name as the command is simpler.

perf: fix a minor typo in perfbranchmapload

context: floor adjustlinkrev graph walk during copy tracing The `_adjustlinkrev` method gains an optional "stoprev" argument. The linkrev adjustment will give up once this floor is reached. The relevant functions using `_adjustlinkrev` are updated to pass an appropriate value in the copy tracing code. In some private repository, about 10% of the status call triggered the pathological case addressed by this change. The speedup varies from one call to another, the best-observed win is moving from 170s to 11s. The effect of this change can be seen in the public pypy repository, running the following command: hg perftracecopies --source 83c9ff0c0206 --destination 59c79103d5b0 before: 3.401753 seconds after: 2.634897 seconds (-23%)