tree 718e6980b758443e0fa81a4823bdb94cdad966e1
parent b0eb744604391c94ec505f846604df1a07a166b1
author Shawn Pearce <spearce@spearce.org> 1448731439 -0800
committer Shawn Pearce <spearce@spearce.org> 1448927200 -0800

DirCacheBuilder: Speed up reading from trees

Recursively copying a tree into a DirCache is a bottleneck for some
algorithms like the in memory merge code in Gerrit Code Review.  Drop
a layer down in the stack and use CanonicalTreeParser directly as the
addition logic only processes 1 tree at a time and does not need the
merge sorting feature (or overhead) of TreeWalk.

Combined with 761814fe9c ("DirCacheEntry: Speed up creation by
avoiding string cast") tree loading 38,900 entries nearly halves
in running time from 70ms to 36ms on some platforms.

Change-Id: If1490ca25de0679a71cf508f59b486f9cc816165