Two changes:

  1. Don't scan to the end of alloca instructions in the caller function to
     insert inlined allocas, just insert at the top.  This saves a lot of
     time inlining into functions with a lot of allocas.
  2. Use splice to move the alloca instructions over, instead of remove/insert.
     This allows us to transfer a block at a time, and eliminates a bunch of
     silly symbol table manipulations.

This speeds up the inliner on the testcase in PR209 from 1.73s -> 1.04s (67%)

llvm-svn: 11118