Hi all,

We got a request to support the RNG intrinsics on GCC 8 as some cores used with this compiler will support the instructions
and the intrinsics are not very invasive to implement.
This does require adding the +rng arch extension to GCC 8, which is simple to do.
Otherwise the patch looks very much like the GCC 9 version

Bootstrapped and tested on aarch64-none-linux gnu on the branch. Pushed.
Thanks,
Kyrill

Hi all,

This patch implements the recently published[1] __rndr and __rndrrs
intrinsics used to access the RNG in Armv8.5-A.
The __rndrrs intrinsics can be used to reseed the generator too.
They are guarded by the __ARM_FEATURE_RNG feature macro.
A quirk with these intrinsics is that they store the random number in
their pointer argument and return a status
code if the generation succeeded.

The instructions themselves write the CC flags indicating the success of
the operation that we can then read with a CSET.
Therefore this implementation makes use of the IGNORE indicator to the
builtin expand machinery to avoid generating
the CSET if its result is unused (the CC reg clobbering effect is still
reflected in the pattern).
I've checked that using unspec_volatile prevents undesirable CSEing of
the instructions.

[1] https://developer.arm.com/docs/101028/latest/data-processing-intrinsics

gcc/
	PR target/71233
	* config/aarch64/aarch64.md (UNSPEC_RNDR, UNSPEC_RNDRRS): Define.
	(aarch64_rndr): New define_insn.
	(aarch64_rndrrs): Likewise.
	* config/aarch64/aarch64.h (AARCH64_ISA_RNG): Define.
	(TARGET_RNG): Likewise.
	(AARCH64_FL_RNG): Likewise.
	* config/aarch64/aarch64-option-extensions.def (rng): Define.
	* config/aarch64/aarch64-builtins.c (enum aarch64_builtins):
	Add AARCH64_BUILTIN_RNG_RNDR, AARCH64_BUILTIN_RNG_RNDRRS.
	(aarch64_init_rng_builtins): Define.
	(aarch64_init_builtins): Call aarch64_init_rng_builtins.
	(aarch64_expand_rng_builtin): Define.
	(aarch64_expand_builtin): Use IGNORE argument, handle
	RNG builtins.
	* config/aarch64/aarch64-c.c (aarch64_update_cpp_builtins): Define
	__ARM_FEATURE_RNG when TARGET_RNG.
	* config/aarch64/arm_acle.h (__rndr, __rndrrs): Define.

gcc/testsuite/
	PR target/71233
	* gcc.target/aarch64/acle/rng_1.c: New test.