[PATCH] [Instcombine] Recognize test for overflow in integer multiplication.

[Erik Verbruggen]

  Could you rename the method to ProcessUMulZExtIdiom? The ProcessUAddIdiom handles a different case, and I have a patch that does the same for UMul.

  Otherwise, LGTM, but bkramer has the final say.

  As a follow-up, are you interested in doing the same for a signed sub and mul? (Add is already handled.) If not, I can do that.

http://reviews.llvm.org/D2814