TargetOpcodes: Rewrite the documentation for SUBREG_TO_REG

Differential Revision: https://reviews.llvm.org/D22708

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278258 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed