[PATCH] aarch64: Use SVE SUBR instruction with Neon modes

[Soumya AR]

The SVE SUBR instruction performs a reversed subtract from an immediate.

This patches enables the emission of SUBR for Neon modes and avoids the need to
materialise an explicit constant.

For example, the below test case:

typedef long long __attribute__ ((vector_size (16))) v2di;

v2di subr_v2di (v2di x)
{
        return 15 - x;
}

compiles to:

subr_v2di:
        mov     z31.d, #15
        sub     v0.2d, v31.2d, v0.2d
        ret

but can just be:

subr_v2di:
        subr    z0.d, z0.d, #15
        ret

The patch was bootstrapped and regtested on aarch64-linux-gnu, no regression.
OK for mainline?

Signed-off-by: Soumya AR <soum...@nvidia.com>

gcc/ChangeLog:

        * config/aarch64/aarch64-simd.md:
        (sub<mode>3<vczle><vczbe>): Extended the pattern to emit SUBR for SVE
        targets if operand 1 is an immediate.
        * config/aarch64/predicates.md (aarch64_sve_arith_imm_or_reg_operand):
        New predicate that accepts aarch64_sve_arith_immediate in operand 1 but
        only for TARGET_SVE.

gcc/testsuite/ChangeLog:

        * gcc.target/aarch64/sve/subr-sve.c: New test.

0001-aarch64-Use-SVE-SUBR-instruction-with-Neon-modes.patch
Description: 0001-aarch64-Use-SVE-SUBR-instruction-with-Neon-modes.patch