Hi,

This is a v3 patch which is rebased on top of the SME changes.
Otherwise it is the same as v2, posted here:

https://gcc.gnu.org/pipermail/gcc-patches/2023-December/639367.html

Bootstrapped/regtested as a series on aarch64-linux-gnu, OK for trunk?

Thanks,
Alex

-- >8 --

Thus far the writeback forms of ldp/stp have been exclusively used in
prologue and epilogue code for saving/restoring of registers to/from the
stack.

As such, forms of ldp/stp that weren't needed for prologue/epilogue code
weren't supported by the aarch64 backend.  This patch generalizes the
load/store pair writeback patterns to allow:

 - Base registers other than the stack pointer.
 - Modes that weren't previously supported.
 - Combinations of distinct modes provided they have the same size.
 - Pre/post variants that weren't previously needed in prologue/epilogue
   code.

We make quite some effort to avoid a combinatorial explosion in the
number of patterns generated (and those in the source) by making
extensive use of special predicates.

An updated version of the upcoming ldp/stp pass can generate the
writeback forms, so this patch is motivated by that.

This patch doesn't add zero-extending or sign-extending forms of the
writeback patterns; that is left for future work.

gcc/ChangeLog:

        * config/aarch64/aarch64-protos.h (aarch64_ldpstp_operand_mode_p): Declare.
        * config/aarch64/aarch64.cc (aarch64_gen_storewb_pair): Build RTL
        directly instead of invoking named pattern.
        (aarch64_gen_loadwb_pair): Likewise.
        (aarch64_ldpstp_operand_mode_p): New.
        * config/aarch64/aarch64.md (loadwb_pair<GPI:mode>_<P:mode>): Replace with
        ...
        (*loadwb_post_pair_<ldst_sz>): ... this. Generalize as described
        in cover letter.
        (loadwb_pair<GPF:mode>_<P:mode>): Delete (superseded by the
        above).
        (*loadwb_post_pair_16): New.
        (*loadwb_pre_pair_<ldst_sz>): New.
        (loadwb_pair<TX:mode>_<P:mode>): Delete.
        (*loadwb_pre_pair_16): New.
        (storewb_pair<GPI:mode>_<P:mode>): Replace with ...
        (*storewb_pre_pair_<ldst_sz>): ... this.  Generalize as
        described in cover letter.
        (*storewb_pre_pair_16): New.
        (storewb_pair<GPF:mode>_<P:mode>): Delete.
        (*storewb_post_pair_<ldst_sz>): New.
        (storewb_pair<TX:mode>_<P:mode>): Delete.
        (*storewb_post_pair_16): New.
        * config/aarch64/predicates.md (aarch64_mem_pair_operator): New.
        (pmode_plus_operator): New.
        (aarch64_ldp_reg_operand): New.
        (aarch64_stp_reg_operand): New.