On 4/29/23 10:25, Roger Sayle wrote:
This patch contains some minor tweak to xstormy16's machine description
most significantly providing a pattern for HImode rotate left by a single
bit that requires only two instructions.
unsigned short foo(unsigned short x)
{
return (x << 1) | (x >> 15);
}
currently with -O2 generates:
foo: mov r7,r2
shr r7,#15
shl r2,#1
or r2,r7
ret
with this patch, GCC now generates:
foo: shl r2,#1 | adc r2,#0
ret
Additionally neghi2 is converted to a define_insn (so that the RTL
optimizers see the negation semantics), and HImode rotations by
8-bits can now be recognized and implemented using swpb.
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 (neghi2): Convert from a define_expand
to a define_insn.
(*rotatehi_1): New define_insn for efficient 2 insn sequence.
(*rotatehi_8, *rotaterthi_8): New define_insn to emit a swpb.
gcc/testsuite/ChangeLog
* gcc.target/xstormy16/neghi2.c: New test case.
* gcc.target/rotatehi-1.c: Likewise.
It may be the case that exposing negation as a not + add sequence was
thought to potentially produce better code by exposing the component
instructions. Or it may have simply been the case that nobody
considered the tradeoffs.
Either way, I think the patch is fine. As is always the case, figure
~24hrs after committing we'll have test results.
jeff
