[globalisel][tablegen] Support zero-instruction emission.
Summary:
Support the case where an operand of a pattern is also the whole of the
result pattern. In this case the original result and all its uses must be
replaced by the operand. However, register class restrictions can require
a COPY. This patch handles both cases by always emitting the copy and
leaving it for the register allocator to optimize.
Depends on D35833
Reviewers: ab, t.p.northover, qcolombet, rovka, aditya_nandakumar
Subscribers: javed.absar, kristof.beyls, igorb, llvm-commits
Differential Revision: https://reviews.llvm.org/D36084
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310716
91177308-0d34-0410-b5e6-
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