[InstCombine] Speculatively implement a fix for what might be the root cause of PR337...

[InstCombine] Speculatively implement a fix for what might be the root cause of PR33721 by making sure that we have integer types before doing select C, -1, 0 -> sext C to int

I recently changed m_One and m_AllOnes to use Constant::isOneValue/isAllOnesValue which work on floating point values too. The original implementation looked specifically for ConstantInt scalars and splats. So I'm guessing we are accidentally trying to issue sext/zexts on floating point types now.

Hopefully I figure out how to reproduce the failure from the PR soon.

llvm-svn: 307486