[PATCH][AArch64][GCC 9] Implement __rndr, __rndrrs intrinsics

Fri, 25 Sep 2020 03:27:09 -0700 

Hi all,

I'd like to backport this patch to the GCC 9 branch implementing the RNG 
intrinsics from Armv8.5-a.
It should have been supported there from the start.
It doesn't apply cleanly since the SVE ACLE work in GCC 10 reworked some of the 
builtin handling,
but the resolution isn't complex.

Bootstrapped, tested and pushed on the branch.
Thanks,
Kyrill

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.
        * 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.

Attachment: rndr-9.patch
Description: rndr-9.patch

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