https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87678
--- Comment #4 from Segher Boessenkool <segher at gcc dot gnu.org> --- It tries twice, first just the substitution, and then that modified with the REG_EQUAL. You know a mem is not often valid in the resulting insn, but combine doesn't, and that is not the same thing as not having a mem in the inputs anyway!
