ifcvt: Avoid ICEs trying to force_operand random RTL [PR97487]

ifcvt: Avoid ICEs trying to force_operand random RTL [PR97487]

As the testcase shows, RTL ifcvt can throw random RTL (whatever it found in
some insns) at expand_binop or expand_unop and expects it to do something
(and then will check if it created valid insns and punts if not).
These functions in the end if the operands don't match try to
copy_to_mode_reg the operands, which does
if (!general_operand (x, VOIDmode))
  x = force_operand (x, temp);
but, force_operand is far from handling all possible RTLs, it will ICE for
all more unusual RTL codes.  Basically handles just simple arithmetic and
unary RTL operations if they have an optab and
expand_simple_binop/expand_simple_unop ICE on others.

The following patch fixes it by adding some operand verification (whether
there is a hope that copy_to_mode_reg will succeed on those).  It is added
both to noce_emit_move_insn (not needed for this exact testcase,
that function simply tries to recog the insn as is and if it fails,
handles some simple binop/unop cases; the patch performs the verification
of their operands) and noce_try_sign_mask.

2021-02-03  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/97487
	* ifcvt.c (noce_can_force_operand): New function.
	(noce_emit_move_insn): Use it.
	(noce_try_sign_mask): Likewise.  Formatting fix.

	* gcc.dg/pr97487-1.c: New test.
	* gcc.dg/pr97487-2.c: New test.