Regalloc creates COPY instructions which do not formally use VALU.
That results in v_mov instructions displaced after exec mask modification.
One pass which do it is SIOptimizeExecMasking, but potentially it can be
done by other passes too.
This patch adds a pass immediately after regalloc to add implicit exec
use operand to all VGPR copy instructions.
Differential Revision: https://reviews.llvm.org/D28874
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@292956 91177308-0d34-0410-b5e6-96231b3b80d8