combine: Fix ICE in try_combine on pr112494.c [PR112560]

combine: Fix ICE in try_combine on pr112494.c [PR112560]

The compiler, configured with --enable-checking=yes,rtl,extra ICEs with:

internal compiler error: RTL check: expected elt 0 type 'e' or 'u', have 'E' (rtx unspec) in try_combine, at combine.cc:3237

This is

3236			  /* Just replace the CC reg with a new mode.  */
3237			  SUBST (XEXP (*cc_use_loc, 0), newpat_dest);
3238			  undobuf.other_insn = cc_use_insn;

in combine.cc, where *cc_use_loc is

(unspec:DI [
        (reg:CC 17 flags)
    ] UNSPEC_PUSHFL)

combine assumes CC must be used inside of a comparison and uses XEXP (..., 0)
without checking on the RTX type of the argument.

Replace cc_use_loc with the entire new RTX only in case cc_use_loc satisfies
COMPARISON_P predicate.  Otherwise scan the entire cc_use_loc RTX for CC reg
to be updated with a new mode.

	PR rtl-optimization/112560

gcc/ChangeLog:

	* combine.cc (try_combine): Replace cc_use_loc with the entire
	new RTX only in case cc_use_loc satisfies COMPARISON_P predicate.
	Otherwise scan the entire cc_use_loc RTX for CC reg to be updated
	with a new mode.
	* config/i386/i386.md (@pushf<mode>2): Allow all CC modes for
	operand 1.