PeepholeOptimizer: Fix for vregs without defs

The PeepholeOptimizer would fail for vregs without a definition. If this
was caused by an undef operand abort to keep the code simple (so we
don't need to add logic everywhere to replicate the undef flag).

Differential Revision: https://reviews.llvm.org/D40763

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322319 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed