What os.path.normcase does is just to lowercase everything. This means that dependencies generated by cl.py, while they work to know if $file needs to be rebuilt if $header changed, doesn't make things chain up such that $header is rebuilt if $xpidl or whatever else changed. While this is not an immediate problem, it is a problem for future improvements such as bug 905973.

I'm not 100% sure about the caching thing. I've had different results with and without caching, sometimes with non-cached being faster. But that's in a VM with weird performance, so I can't tell for sure.

Comment on attachment 793847 [details] [diff] [review] Use GetShortPathName/GetLongPathName to canonicalize paths for dependency files generated by cl.py Review of attachment 793847 [details] [diff] [review]: ----------------------------------------------------------------- Were you able to isolate the overhead of this? But if it makes dependencies proper, then I suppose it's a cost we need to pay.