perf: add a perfignore command

The command is meant to benchmark operations related to hgignore. Right now the
command is benchmarking the loading time of the hgignore rules.

contrib/perf.py

@@ -975,6 +975,23 b' def perfchangeset(ui, repo, rev, **opts)'
     timer(d)
     fm.end()
 
+@command(b'perfignore', formatteropts)
+def perfignore(ui, repo, **opts):
+    """benchmark operation related to computing ignore"""
+    opts = _byteskwargs(opts)
+    timer, fm = gettimer(ui, opts)
+    dirstate = repo.dirstate
+
+    def setupone():
+        dirstate.invalidate()
+        clearfilecache(dirstate, b'_ignore')
+
+    def runone():
+        dirstate._ignore
+
+    timer(runone, setup=setupone, title=b"load")
+    fm.end()
+
 @command(b'perfindex', formatteropts)
 def perfindex(ui, repo, **opts):
     import mercurial.revlog

tests/test-contrib-perf.t

@@ -86,6 +86,7 b' perfstatus'
    perfhelper-pathcopies
                  find statistic about potential parameters for the
                  'perftracecopies'
+   perfignore    benchmark operation related to computing ignore
    perfindex     (no help text available)
    perflinelogedits
                  (no help text available)
@@ -166,6 +167,7 b' perfstatus'
   fncache already up to date
 #endif
   $ hg perfheads
+  $ hg perfignore
   $ hg perfindex
   $ hg perflinelogedits -n 1
   $ hg perfloadmarkers