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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/106518] Exchange/swap aware register
 allocation (generate xchg in reload)
Date: Wed, 26 Apr 2023 08:11:24 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106518

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Roger Sayle <sayle@gcc.gnu.org>:

https://gcc.gnu.org/g:1f0bfbb26e532cef7347a91439008114fd88173a

commit r14-245-g1f0bfbb26e532cef7347a91439008114fd88173a
Author: Roger Sayle <roger@nextmovesoftware.com>
Date:   Wed Apr 26 09:10:06 2023 +0100

    [xstormy16] Add support for byte and word swapping instructions.

    This patch adds support for xstormy16's swpb (swap bytes) and swpw (swap
    words) instructions.  The most obvious application of these to implement
    the __builtin_bswap16 and __builtin_bswap32 intrinsics.

    Currently, __builtin_bswap16 is implemented as:
    foo:    mov r7,r2
            shl r7,#8
            shr r2,#8
            or r2,r7
            ret

    but with this patch becomes:
    foo:    swpb r2
            ret

    Likewise, __builtin_bswap32 now becomes:
    foo:    swpb r2 | swpb r3 | swpw r2,r3
            ret

    Finally, the swpw instruction on its own can be used to exchange
    two word mode registers without a temporary, so a new pattern and
    peephole2 have been added to catch this.  As described in the
    PR rtl-optimization/106518, register allocation can (in theory)
    be more efficient on targets that provide a swap/exchange instruction.
    The slightly unusual swap<mode> naming matches that used in i386.md.

    2024-04-26  Roger Sayle  <roger@nextmovesoftware.com>

    gcc/ChangeLog
            * config/stormy16/stormy16.md (bswaphi2): New define_insn.
            (bswapsi2): New define_insn.
            (swaphi): New define_insn to exchange two registers (swpw).
            (define_peephole2): Recognize exchange of registers as swaphi.

    gcc/testsuite/ChangeLog
            * gcc.target/xstormy16/bswap16.c: New test case.
            * gcc.target/xstormy16/bswap32.c: Likewise.
            * gcc.target/xstormy16/swpb.c: Likewise.
            * gcc.target/xstormy16/swpw-1.c: Likewise.
            * gcc.target/xstormy16/swpw-2.c: Likewise.=