https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109812
--- Comment #18 from Uroš Bizjak <ubizjak at gmail dot com> ---
One interesting observation:
clang is able to do this:
0.09 │ │ vmovddup -0x8(%rdx,%rsi,1),%xmm3 ▒
...
0.11 │ │ vfmadd231sd %xmm2,%xmm3,%xmm1 ▒
...
0.74 │ │ vfmadd231pd %xmm2,%xmm3,%xmm0 ▒
It figures out that duplicated V2DFmode value in %xmm3 can also be accessed in
the same register as DFmode value.
OTOH, current gcc does:
vmovsd (%rsi,%rax,8), %xmm1
...
vmovddup %xmm1, %xmm4
...
vfmadd231pd %xmm4, %xmm0, %xmm2
...
vfmadd231sd %xmm1, %xmm0, %xmm3
The above code needs two registers.
