RISC-V: Add Ztso atomic mappings

The RISC-V Ztso extension currently has no effect on generated code.
With the additional ordering constraints guarenteed by Ztso, we can emit
more optimized atomic mappings than the RVWMO mappings.

This PR implements the Ztso psABI mappings[1].

[1] https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/391



2023-08-08 Patrick O'Neill <patrick@rivosinc.com>

gcc/ChangeLog:

	* common/config/riscv/riscv-common.cc: Add Ztso and mark Ztso as
	dependent on 'a' extension.
	* config/riscv/riscv-opts.h (MASK_ZTSO): New mask.
	(TARGET_ZTSO): New target.
	* config/riscv/riscv.cc (riscv_memmodel_needs_amo_acquire): Add
	Ztso case.
	(riscv_memmodel_needs_amo_release): Add Ztso case.
	(riscv_print_operand): Add Ztso case for LR/SC annotations.
	* config/riscv/riscv.md: Import sync-rvwmo.md and sync-ztso.md.
	* config/riscv/riscv.opt: Add Ztso target variable.
	* config/riscv/sync.md (mem_thread_fence_1): Expand to RVWMO or
	Ztso specific insn.
	(atomic_load<mode>): Expand to RVWMO or Ztso specific insn.
	(atomic_store<mode>): Expand to RVWMO or Ztso specific insn.
	* config/riscv/sync-rvwmo.md: New file. Seperate out RVWMO
	specific load/store/fence mappings.
	* config/riscv/sync-ztso.md: New file. Seperate out Ztso
	specific load/store/fence mappings.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/amo-table-ztso-amo-add-1.c: New test.
	* gcc.target/riscv/amo-table-ztso-amo-add-2.c: New test.
	* gcc.target/riscv/amo-table-ztso-amo-add-3.c: New test.
	* gcc.target/riscv/amo-table-ztso-amo-add-4.c: New test.
	* gcc.target/riscv/amo-table-ztso-amo-add-5.c: New test.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-1.c: New test.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-2.c: New test.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-3.c: New test.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-4.c: New test.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-5.c: New test.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-6.c: New test.
	* gcc.target/riscv/amo-table-ztso-compare-exchange-7.c: New test.
	* gcc.target/riscv/amo-table-ztso-fence-1.c: New test.
	* gcc.target/riscv/amo-table-ztso-fence-2.c: New test.
	* gcc.target/riscv/amo-table-ztso-fence-3.c: New test.
	* gcc.target/riscv/amo-table-ztso-fence-4.c: New test.
	* gcc.target/riscv/amo-table-ztso-fence-5.c: New test.
	* gcc.target/riscv/amo-table-ztso-load-1.c: New test.
	* gcc.target/riscv/amo-table-ztso-load-2.c: New test.
	* gcc.target/riscv/amo-table-ztso-load-3.c: New test.
	* gcc.target/riscv/amo-table-ztso-store-1.c: New test.
	* gcc.target/riscv/amo-table-ztso-store-2.c: New test.
	* gcc.target/riscv/amo-table-ztso-store-3.c: New test.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-1.c: New test.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-2.c: New test.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-3.c: New test.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-4.c: New test.
	* gcc.target/riscv/amo-table-ztso-subword-amo-add-5.c: New test.

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>