Use-and-clobber insns and some ancient combine.c code

[Richard Kenner]

    If (reg X) is not a fixed register, the pattern usually can be written
    using a match_operand and a sufficiently restrictive constraint.
    So in this case, we can either use a pseudo, or make combine
    verify that there is a constraint which has no earlyclobber modifier.

You mean verify there is no constraint with a earlyclobber marker.
Yes, that's safe.