[PATCH] Speed up modules compilation.

[Manuel Klimek]

In http://reviews.llvm.org/D9498#167143, @silvas wrote:

> Numbers on the speedup?


On my tests this is a 40% speedup for a TU using ~1000 transitive modules. I didn't include the number in the description because it is misleading; we are still merging too much, and we have merging-heavy TUs.


http://reviews.llvm.org/D9498

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