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Re: Speedup CSE by 5%
> There are two possible reasons for the copy_rtx I can think of: either
> fold_rtx destructively modifies its input (which I shouldn't happen from
> what I can see), or we have RTL sharing issues. In the latter case, we
> can postpone the copy until after we found that fold_rtx has made a change.
But if X points to a part of INSN, we may be indirectly modifying X
through modifications to INSN.