PowerPC: Add support for 1,024 bit DMR registers.

PowerPC: Add support for 1,024 bit DMR registers.

This patch is a prelimianry patch to add the full 1,024 bit dense math register
(DMRs) for -mcpu=future.  The MMA 512-bit accumulators map onto the top of the
DMR register.

This patch only adds the new 1,024 bit register support.  It does not add
support for any instructions that need 1,024 bit registers instead of 512 bit
registers.

I used the new mode 'TDOmode' to be the opaque mode used for 1,204 bit
registers.  The 'wD' constraint added in previous patches is used for these
registers.  I added support to do load and store of DMRs via the VSX registers,
since there are no load/store dense math instructions.  I added the new keyword
'__dmr' to create 1,024 bit types that can be loaded into DMRs.  At present, I
don't have aliases for __dmr512 and __dmr1024 that we've discussed internally.

The patches have been tested on the following platforms.  I added the patches
for PR target/107299 that I submitted on November 2nd before doing the builds so
that GCC would build on systems using IEEE 128-bit long double.
    *	https://gcc.gnu.org/pipermail/gcc-patches/2022-November/604834.html

The new __dmr type that is being added as a possible future PowerPC instruction
set bumps into a structure field size issue.  The size of the __dmr type is 1024 bits.
The precision field in tree_type_common is currently 10 bits, so if you store
1,024 into field, you get a 0 back.  When you get 0 in the precision field, the
ccp pass passes this 0 to sext_hwi in hwint.h.  That function in turn generates
a shift that is equal to the host wide int bit size, which is undefined as
machine dependent for shifting in C/C++.

      int shift = HOST_BITS_PER_WIDE_INT - prec;
      return ((HOST_WIDE_INT) ((unsigned HOST_WIDE_INT) src << shift)) >> shift;

It turns out the x86_64 where I first did my tests returns the original input
before the two shifts, while the PowerPC always returns 0.  In the ccp pass, the
original input is -1, and so it worked.  When I did the runs on the PowerPC, the
result was 0, which ultimately led to the failure.

In addition, once the precision field is larger, it will help PR C/102989 (C2x
_BigInt) as well as the implementation of the SET_TYPE_VECTOR_SUBPARTS macro.

2023-09-28   Michael Meissner  <meissner@linux.ibm.com>

gcc/

	* config/rs6000/mma.md (UNSPEC_DM_INSERT512_UPPER): New unspec.
	(UNSPEC_DM_INSERT512_LOWER): Likewise.
	(UNSPEC_DM_EXTRACT512): Likewise.
	(UNSPEC_DMR_RELOAD_FROM_MEMORY): Likewise.
	(UNSPEC_DMR_RELOAD_TO_MEMORY): Likewise.
	(movtdo): New define_expand and define_insn_and_split to implement 1,024
	bit DMR registers.
	(movtdo_insert512_upper): New insn.
	(movtdo_insert512_lower): Likewise.
	(movtdo_extract512): Likewise.
	(reload_dmr_from_memory): Likewise.
	(reload_dmr_to_memory): Likewise.
	* config/rs6000/rs6000-builtin.cc (rs6000_type_string): Add DMR
	support.
	(rs6000_init_builtins): Add support for __dmr keyword.
	* config/rs6000/rs6000-call.cc (rs6000_return_in_memory): Add support
	for TDOmode.
	(rs6000_function_arg): Likewise.
	* config/rs6000/rs6000-modes.def (TDOmode): New mode.
	* config/rs6000/rs6000.cc (rs6000_hard_regno_nregs_internal): Add
	support for TDOmode.
	(rs6000_hard_regno_mode_ok_uncached): Likewise.
	(rs6000_hard_regno_mode_ok): Likewise.
	(rs6000_modes_tieable_p): Likewise.
	(rs6000_debug_reg_global): Likewise.
	(rs6000_setup_reg_addr_masks): Likewise.
	(rs6000_init_hard_regno_mode_ok): Add support for TDOmode.  Setup reload
	hooks for DMR mode.
	(reg_offset_addressing_ok_p): Add support for TDOmode.
	(rs6000_emit_move): Likewise.
	(rs6000_secondary_reload_simple_move): Likewise.
	(rs6000_secondary_reload_class): Likewise.
	(rs6000_mangle_type): Add mangling for __dmr type.
	(rs6000_dmr_register_move_cost): Add support for TDOmode.
	(rs6000_split_multireg_move): Likewise.
	(rs6000_invalid_conversion): Likewise.
	* config/rs6000/rs6000.h (VECTOR_ALIGNMENT_P): Add TDOmode.
	(enum rs6000_builtin_type_index): Add DMR type nodes.
	(dmr_type_node): Likewise.
	(ptr_dmr_type_node): Likewise.

gcc/testsuite/

	* gcc.target/powerpc/dm-1024bit.c: New test.