Re: [PATCH] Don't update unchanged merge entries

On Sun, 16 Mar 2008, Linus Torvalds wrote:

In commit 34110cd4e394e3f92c01a4709689b384c34645d8 ("Make 'unpack_trees()' 
have a separate source and destination index") I introduced a really 
stupid bug in that it would always add merged entries with the CE_UPDATE 
flag set. That caused us to always re-write the file, even when it was 
already up-to-date in the source index.

Not only is that really stupid from a performance angle, but more 
importantly it's actively wrong: if we have dirty state in the tree when 
we merge, overwriting it with the result of the merge will incorrectly 
overwrite that dirty state.

This trivially fixes the problem - simply don't set the CE_UPDATE flag 
when the merge result matches the old state.

While you're at it, you should at least fix the comment. I actually think 
it would be better to have update start out 0 and be set to CE_UPDATE 
after verify_uptodate() and verify_absent(), since those checks are what 
verifies that using CE_UPDATE is okay.

	-Daniel
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