Under certain conditions register_operand predicate also allows
subregs of memory operands.  When RTL checking is enabled, these
will fail with REGNO (op).

Allow subregs of memory operands, these are guaranteed
to be reloaded to a register.

2022-06-13  Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog:

    PR target/105927
    * config/i386/predicates.md (register_no_elim_operand):
    Return true for subreg of a memory operand.

gcc/testsuite/ChangeLog:

    PR target/105927
    * gcc.target/i386/pr105927.c: New test.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Pushed to master.

Uros.