[BypassSlowDivision] Refactor fast division insertion logic (NFC)

The most important goal of the patch is to break large insertFastDiv function
into separate pieces, so that later a different fast insertion logic can be
implemented using some of these pieces.

Differential Revision: https://reviews.llvm.org/D29896


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296828 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed