[PATCH 08 of 10 V4] context: floor adjustlinkrev graph walk during copy tracing

[Boris Feld]

# HG changeset patch
# User Boris Feld <boris.feld at octobus.net>
# Date 1536255188 14400
#      Thu Sep 06 13:33:08 2018 -0400
# Node ID 53c0bf99c013909bd628aa5254c26d301236ba26
# Parent  462edcfdf6346b522eee9a64c5c1ca9ff566d7b8
# EXP-Topic copy-perf
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 53c0bf99c013
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.

diff --git a/mercurial/context.py b/mercurial/context.py
--- a/mercurial/context.py
+++ b/mercurial/context.py
@@ -719,7 +719,7 @@ class basefilectx(object):
 
         return True
 
-    def _adjustlinkrev(self, srcrev, inclusive=False):
+    def _adjustlinkrev(self, srcrev, inclusive=False, stoprev=None):
         """return the first ancestor of <srcrev> introducing <fnode>
 
         If the linkrev of the file revision does not point to an ancestor of
@@ -728,6 +728,10 @@ class basefilectx(object):
 
         :srcrev: the changeset revision we search ancestors from
         :inclusive: if true, the src revision will also be checked
+        :stoprev: an optional revision to stop the walk at. If no introduction
+                  of this file content could be found before this floor
+                  revision, the function will returns "None" and stops its
+                  iteration.
         """
         repo = self._repo
         cl = repo.unfiltered().changelog
@@ -755,6 +759,8 @@ class basefilectx(object):
             fnode = self._filenode
             path = self._path
             for a in iteranc:
+                if stoprev is not None and a < stoprev:
+                    return None
                 ac = cl.read(a) # get changeset data (we avoid object creation)
                 if path in ac[3]: # checking the 'files' field.
                     # The file has been touched, check if the content is
@@ -770,8 +776,12 @@ class basefilectx(object):
     def isintroducedafter(self, changelogrev):
         """True if a filectx have been introduced after a given floor revision
         """
-        return (self.linkrev() > changelogrev
-                or self._introrev() > changelogrev)
+        if self.linkrev() > changelogrev:
+            return True
+        introrev = self._introrev(stoprev=changelogrev)
+        if introrev is None:
+            return False
+        return introrev > changelogrev
 
     def introrev(self):
         """return the rev of the changeset which introduced this file revision
@@ -784,7 +794,15 @@ class basefilectx(object):
         """
         return self._introrev()
 
-    def _introrev(self):
+    def _introrev(self, stoprev=None):
+        """
+        Same as `introrev` but, with an extra argument to limit changelog
+        iteration range in some internal usecase.
+
+        If `stoprev` is set, the `introrev` will not be searched past that
+        `stoprev` revision and "None" might be returned. This is useful to
+        limit the iteration range.
+        """
         toprev = None
         attrs = vars(self)
         if r'_changeid' in attrs:
@@ -795,11 +813,12 @@ class basefilectx(object):
             toprev = self._changectx.rev()
 
         if toprev is not None:
-            return self._adjustlinkrev(toprev, inclusive=True)
+            return self._adjustlinkrev(toprev, inclusive=True, stoprev=stoprev)
         elif r'_descendantrev' in attrs:
-            introrev = self._adjustlinkrev(self._descendantrev)
+            introrev = self._adjustlinkrev(self._descendantrev, stoprev=stoprev)
             # be nice and cache the result of the computation
-            self._changeid = introrev
+            if introrev is not None:
+                self._changeid = introrev
             return introrev
         else:
             return self.linkrev()