copies: do full filtering at end of _changesetforwardcopies() As mentioned earlier, pathcopies() is very slow when copies are stored in the changeset. Most of the cost comes from calling _chain() for every changeset, which is slow because it needs to read manifests. It needs to read manifests to be able to filter out copies that are were created in one commit and then deleted. (It also filters out copies that were created from a file that didn't exist in the starting revision, but that's a fixed revision across calls to _chain(), so it's much cheaper.) This patch changes from _chainandfilter() to just _chain() in the main loop in _changesetforwardcopies(). It instead removes copies that have subsequently been removed by using ctx.filesremoved(). We thus rely on that to be fast. It timed this command in mozilla-unified: hg debugpathcopies FIREFOX_59_0b3_BUILD2 FIREFOX_BETA_59_END It took 18s before and 1.1s after. It's still faster when copy information is stored in filelogs: 0.70s. It also still gets slow when there are merge commits involved, because we read manifests there too. We'll deal with that later. Differential Revision: https://phab.mercurial-scm.org/D6419

--- a/mercurial/copies.py	Sat Jun 15 10:58:53 2019 +0900
+++ b/mercurial/copies.py	Thu Apr 18 00:40:53 2019 -0700
@@ -300,6 +300,7 @@
         else:
             copies = copies1
         if r == b.rev():
+            _filter(a, b, copies)
             return copies
         for c in children[r]:
             childctx = repo[c]
@@ -313,7 +314,10 @@
             if not match.always():
                 childcopies = {dst: src for dst, src in childcopies.items()
                                if match(dst)}
-            childcopies = _chainandfilter(a, childctx, copies, childcopies)
+            childcopies = _chain(copies, childcopies)
+            for f in childctx.filesremoved():
+                if f in childcopies:
+                    del childcopies[f]
             heapq.heappush(work, (c, parent, childcopies))
     assert False