On Tue, 29 Jul 2025, Robin Dapp wrote:
> > - if (len >= 3
> > + if (!reassoc_insert_powi_p
> > + && len >= 3
> > && (!has_fma
> > /* width > 1 means ranking ops results in better
> > parallelism. Check current value to avoid
>
> Last time I tried this I saw x86 regressions in bswap test cases (hence we
> decided not to go forward with it). I'm assuming they didn't show up in your
> regtest but I wonder what's different now.
>
> > FAIL: gcc.target/i386/pr115102.c scan-assembler bswaphisi2_lowpart
> > FAIL: gcc.target/i386/xchg-4.c scan-assembler rolw
> > FAIL: gcc.target/i386/xchg-4.c scan-assembler-not mov
They did, but somehow I thought they must come from an unrelated
change. They could be fixed by allowing == 3 ops re-assocs but
in the end improving rotate detection in forwprop and bswap
in the bswap pass would be better. It's also that == 3 will
still break reduction chains, just for 2 elements:
double
frd (double *p, double *lastone)
{
double sum = 0;
for (; p <= lastone; p += 2)
sum += p[0] + p[1];
return sum;
}
I'll add a testcase for that case as well.
Richard.
