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 <ro...@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
