[InstCombine] don't propagate wider shufflevector arguments to predecessors

[InstCombine] don't propagate wider shufflevector arguments to predecessors

InstCombine would propagate shufflevector insts that had wider output vectors onto
predecessors, which would sometimes push undef's onto the divisor of a div/rem and
result in bad codegen.

I've fixed this by just banning propagating shufflevector back if the result of
the shufflevector is wider than the input vectors.

Patch by: @sheredom (Neil Henning)

Differential Revision: https://reviews.llvm.org/D52548

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343329 91177308-0d34-0410-b5e6-96231b3b80d8