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

[Jeff Law <jeffreyalaw@gmail.com>]

On 4/25/23 14:20, Roger Sayle wrote:
> 
> 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.
> 
> This patch has been tested by building a cross-compiler to xstormy16-elf
> from x86_64-pc-linux-gnu, and confirming the new test cases pass.
> Ok for mainline?
> 
> 
> 2024-04-25  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.
OK.  And like prior patches, if it causes any problems in wider testing, 
we'll know ~24hrs after the bits go in.

jeff