nvptx: PTX 'alloca' for '-mptx=7.3'+, '-march=sm_52'+ [PR65181]

nvptx: PTX 'alloca' for '-mptx=7.3'+, '-march=sm_52'+ [PR65181]

..., and use it for '-mno-soft-stack': PTX "native" stacks.

	PR target/65181
	gcc/
	* config/nvptx/nvptx.cc (nvptx_get_drap_rtx): Handle
	'!TARGET_SOFT_STACK'.
	* config/nvptx/nvptx.md (define_c_enum "unspec"): Add
	'UNSPEC_STACKSAVE', 'UNSPEC_STACKRESTORE'.
	(define_expand "allocate_stack", define_expand "save_stack_block")
	(define_expand "save_stack_block"): Handle '!TARGET_SOFT_STACK',
	PTX 'alloca'.
	(define_insn "@nvptx_alloca_<mode>")
	(define_insn "@nvptx_stacksave_<mode>")
	(define_insn "@nvptx_stackrestore_<mode>"): New.
	* doc/invoke.texi (Nvidia PTX Options): Update '-msoft-stack',
	'-mno-soft-stack'.
	* doc/sourcebuild.texi (nvptx-specific attributes): Document
	'nvptx_runtime_alloca_ptx'.
	(Add Options): Document 'nvptx_alloca_ptx'.
	gcc/testsuite/
	* gcc.target/nvptx/alloca-1.c: Evolve into...
	* gcc.target/nvptx/alloca-1-O0.c: ... this, ...
	* gcc.target/nvptx/alloca-1-O1.c: ... this, and...
	* gcc.target/nvptx/alloca-1-sm_30.c: ... this.
	* gcc.target/nvptx/vla-1.c: Evolve into...
	* gcc.target/nvptx/vla-1-O0.c: ... this, ...
	* gcc.target/nvptx/vla-1-O1.c: ... this, and...
	* gcc.target/nvptx/vla-1-sm_30.c: ... this.
	* gcc.c-torture/execute/pr36321.c: Adjust.
	* gcc.target/nvptx/__builtin_alloca_0-1-O0.c: Likewise.
	* gcc.target/nvptx/__builtin_alloca_0-1-O1.c: Likewise.
	* gcc.target/nvptx/__builtin_stack_save___builtin_stack_restore-1.c:
	Likewise.
	* gcc.target/nvptx/softstack.c: Likewise.
	* gcc.target/nvptx/__builtin_stack_save___builtin_stack_restore-1-sm_30.c:
	New.
	* gcc.target/nvptx/alloca-2-O0.c: Likewise.
	* gcc.target/nvptx/alloca-3-O1.c: Likewise.
	* gcc.target/nvptx/alloca-4-O3.c: Likewise.
	* gcc.target/nvptx/alloca-5.c: Likewise.
	* lib/target-supports.exp (check_effective_target_alloca): Adjust.
	(check_nvptx_default_ptx_isa_target_architecture_at_least)
	(check_nvptx_runtime_ptx_isa_target_architecture_at_least)
	(check_effective_target_nvptx_runtime_alloca_ptx)
	(add_options_for_nvptx_alloca_ptx): New.
	libgomp/
	* fortran.c (omp_get_device_from_uid_): Adjust.
	* testsuite/libgomp.oacc-fortran/privatized-ref-2.f90: Likewise.