Add IEEE 128-bit fp conditional move on PowerPC.

Add IEEE 128-bit fp conditional move on PowerPC.

This patch adds the support for power10 IEEE 128-bit floating point conditional
move and for automatically generating min/max.

In this patch, I simplified things compared to previous patches.  Instead of
allowing any four of the modes to be used for the conditional move comparison
and the move itself could use different modes, I restricted the conditional
move to just the same mode.  I.e. you can do:

    _Float128 a, b, c, d, e, r;

    r = (a == b) ? c : d;

But you can't do:

    _Float128 c, d, r;
    double a, b;

    r = (a == b) ? c : d;

or:

    _Float128 a, b;
    double c, d, r;

    r = (a == b) ? c : d;

This eliminates a lot of the complexity of the code, because you don't have to
worry about the sizes being different, and the IEEE 128-bit types being
restricted to Altivec registers, while the SF/DF modes can use any VSX
register.

I did not modify the existing support that allowed conditional moves where
SFmode operands are compared and DFmode operands are moved (and vice versa).

I modified the test cases that I added to reflect this change.  I have also
fixed the test for not equal to use '!=' instead of '=='.

2021-07-01 Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/rs6000.c (rs6000_maybe_emit_fp_cmove): Add IEEE
	128-bit floating point conditional move support.
	(have_compare_and_set_mask): Add IEEE 128-bit floating point
	types.
	* config/rs6000/rs6000.md (mov<mode>cc, IEEE128 iterator): New insn.
	(mov<mode>cc_p10, IEEE128 iterator): New insn.
	(mov<mode>cc_invert_p10, IEEE128 iterator): New insn.
	(fpmask<mode>, IEEE128 iterator): New insn.
	(xxsel<mode>, IEEE128 iterator): New insn.

gcc/testsuite/

	* gcc.target/powerpc/float128-cmove.c: New test.
	* gcc.target/powerpc/float128-minmax-3.c: New test.