[InlineSpiller] Don't spill fully undef values

Althought it is not wrong to spill undef values, it is useless and harms
both code size and runtime. Before spilling a value, check that its
content actually matters.

http://www.llvm.org/PR33311

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304752 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed