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List:       gcc-patches
Subject:    Re: [xstormy16 PATCH] Recognize/support swpn (swap nibbles) instruction.
From:       Jeff Law via Gcc-patches <gcc-patches () gcc ! gnu ! org>
Date:       2023-04-29 16:44:44
Message-ID: 9647ad55-6b6b-d0c9-9fe4-2095b41bf02a () gmail ! com
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On 4/29/23 10:24, Roger Sayle wrote:
> 
> This patch adds support for xstormy16's swap nibbles instruction (swpn).
> For the test case:
> 
> short foo(short x) {
>    return (x&0xff00) | ((x<<4)&0xf0) | ((x>>4)&0x0f);
> }
> 
> GCC with -O2 currently generates the nine instruction sequence:
> foo:    mov r7,r2
>          asr r2,#4
>          and r2,#15
>          mov.w r6,#-256
>          and r6,r7
>          or r2,r6
>          shl r7,#4
>          and r7,#255
>          or r2,r7
>          ret
> 
> with this patch, we now generate:
> foo:    swpn r2
>          ret
> 
> To achieve this using combine's four instruction "combinations" requires
> a little wizardry.  Firstly, define_insn_and_split are introduced to
> treat logical shifts followed by bitwise-AND as macro instructions that
> are split after reload.  This is sufficient to recognize a QImode
> nibble swap, which can be implemented by swpn followed by either a
> zero-extension or a sign-extension from QImode to HImode.  Then finally,
> in the correct context, a QImode swap-nibbles pattern can be combined to
> preserve the high-byte of a HImode word, matching the xstormy16's swpn
> semantics.
> 
> The naming of the new code iterators is taken from i386.md.
> The any_rotate code iterator is used in my next (split out) patch.
> 
> 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?
> 
> 
> 2023-04-29  Roger Sayle  <roger@nextmovesoftware.com>
> 
> gcc/ChangeLog
>          * config/stormy16/stormy16.md (any_lshift): New code iterator.
>          (any_or_plus): Likewise.
>          (any_rotate): Likewise.
>          (*<any_lshift>_and_internal): New define_insn_and_split to
>          recognize a logical shift followed by an AND, and split it
>          again after reload.
>          (*swpn): New define_insn matching xstormy16's swpn.
>          (*swpn_zext): New define_insn recognizing swpn followed by
>          zero_extendqihi2, i.e. with the high byte set to zero.
>          (*swpn_sext): Likewise, for swpn followed by cbw.
>          (*swpn_sext_2): Likewise, for an alternate RTL form.
>          (*swpn_zext_ior): A pre-reload splitter so that an swpn+zext+ior
>          sequence is split in the correct place to recognize the *swpn_zext
>          followed by any_or_plus (ior, xor or plus) instruction.
> 
> gcc/testsuite/ChangeLog
>          * gcc.target/xstormy16/swpn-1.c: New QImode test case.
>          * gcc.target/xstormy16/swpn-2.c: New zero_extend test case.
>          * gcc.target/xstormy16/swpn-3.c: New sign_extend test case.
>          * gcc.target/xstormy16/swpn-4.c: New HImode test case.
Ah, bridge patterns.

OK for the trunk.

jeff
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