Power10: Add options to disable load and store vector pair.

Power10: Add options to disable load and store vector pair.

In working on some future patches that involve utilizing vector pair
instructions, I wanted to be able to tune my program to enable or disable using
the vector pair load or store operations while still keeping the other
operations on the vector pair.

This patch adds two undocumented tuning options.  The -mno-load-vector-pair
option would tell GCC to generate two load vector instructions instead of a
single load vector pair.  The -mno-store-vector-pair option would tell GCC to
generate two store vector instructions instead of a single store vector pair.

If either -mno-load-vector-pair is used, GCC will not generate the indexed
stxvpx instruction.  Similarly if -mno-store-vector-pair is used, GCC will not
generate the indexed lxvpx instruction.  The reason for this is to enable
splitting the {,p}lxvp or {,p}stxvp instructions after reload without needing a
scratch GPR register.

The current default for -mcpu=power10 is that both load vector pair and store
vector pair are enabled.

I decided that if the user explicitly used the __builtin_vsx_lxvp or the
__builtin_vsx_stxvp built-in functions to load or store a vector pair, that
those functions would always generate a vector pair instruction.

I added code so that the user code modify these settings using either a
'#pragma GCC target' directive or used __attribute__((__target__(...))) in the
function declaration.

I added tests for the switches, #pragma, and attribute options.

I have built this on both little endian power10 systems and big endian power9
systems doing the normal bootstrap and test.  There were no regressions in any
of the tests, and the new tests passed.  Can I check this patch into the master
branch?

2023-10-12  Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/mma.md (movoo): Add support for -mload-vector-pair and
	-mstore-vector-pair.
	* config/rs6000/rs6000-cpus.def (OTHER_POWER10_MASKS): Likewise.
	(POWERPC_MASKS): Likewise.
	* config/rs6000/rs6000.md (rs6000_setup_reg_addr_masks): If either load
	vector pair or store vector pair instructions are not being generated,
	don't allow lxvpx or stxvpx to be generated.
	(rs6000_option_override_internal): Add warnings if either
	-mload-vector-pair or -mstore-vector-pair is used without having MMA
	instructions.
	(rs6000_opt_masks): Allow user to override -mload-vector-pair or
	-mstore-vector-pair via #pragma or attribute.
	* config/rs6000/rs6000.opt (-mload-vector-pair): New option.
	(-mstore-vector-pair): Likewise.

gcc/testsuite/

	* gcc.target/powerpc/vector-pair-attribute.c: New test.
	* gcc.target/powerpc/vector-pair-pragma.c: New test.
	* gcc.target/powerpc/vector-pair-switch1.c: New test.
	* gcc.target/powerpc/vector-pair-switch2.c: New test.
	* gcc.target/powerpc/vector-pair-switch3.c: New test.
	* gcc.target/powerpc/vector-pair-switch4.c: New test.