[AArch64][1/4] Support Return address protection on AArch64

[AArch64][1/4] Support Return address protection on AArch64

gcc/
	* config/aarch64/aarch64-opts.h (aarch64_function_type): New enum.
	* config/aarch64/aarch64-protos.h
	(aarch64_return_address_signing_enabled): New declaration.
	* config/aarch64/aarch64.c (aarch64_return_address_signing_enabled):
	New function.
	(aarch64_expand_prologue): Sign return address before it's pushed onto
	stack.
	(aarch64_expand_epilogue): Authenticate return address fetched from
	stack.
	(aarch64_override_options): Sanity check for ILP32 and ISA level.
	(aarch64_attributes): New function attributes for "sign-return-address".
	* config/aarch64/aarch64.md (UNSPEC_AUTI1716, UNSPEC_AUTISP,
	UNSPEC_PACI1716, UNSPEC_PACISP, UNSPEC_XPACLRI): New unspecs.
	("*do_return"): Generate combined instructions according to key index.
	("<pauth_mnem_prefix>sp", "<pauth_mnem_prefix1716", "xpaclri"): New.
	* config/aarch64/iterators.md (PAUTH_LR_SP, PAUTH_17_16): New integer
	iterators.
	(pauth_mnem_prefix, pauth_hint_num_a): New integer attributes.
	* config/aarch64/aarch64.opt (msign-return-address=): New.
	* doc/extend.texi (AArch64 Function Attributes): Documents
	"sign-return-address=".
	* doc/invoke.texi (AArch64 Options): Documents "-msign-return-address=".

gcc/testsuite/
	* gcc.target/aarch64/return_address_sign_1.c: New testcase for no
	combined instructions.
	* gcc.target/aarch64/return_address_sign_2.c: New testcase for combined
	instructions.
	* gcc.target/aarch64/return_address_sign_3.c: New testcase for disable
	of pointer authentication.

From-SVN: r244666