From: peter.noreply@tin.it
On Sat, 19 Jul 2025 10:18:15 GMT
anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:
> peter writes:
> >I did a test coding the sum128 as a code word with avx-512 instructions
> >and got the following results
> >
> > 285,584,376 cycles:u
> > 941,856,077 instructions:u
> >
> >timing was
> >timer-reset ' recursive-sum bench .elapsed 51 ms elapsed
> >
> >so half the time of the original recursive.
> >with 32 zmm registers I could have done a sum256 also
>
> One could do sum128 with just 8 registers by performing the adds ASAP,
> i.e., for sum32
>
> vmovapd zmm0, [rbx]
> vmovapd zmm1, [rbx+64]
> vaddpd zmm0, zmm0, zmm1
> vmovapd zmm1, [rbx+128]
> vmovapd zmm2, [rbx+192]
> vaddpd zmm1, zmm1, zmm2
> vaddpd zmm0, zmm0, zmm1
> ; and then the Horizontal sum
>
> And you can code this as:
>
> vmovapd zmm0, [rbx]
> vaddpd zmm0, zmm0, [rbx+64]
> vmovapd zmm1, [rbx+128]
> vaddpd zmm1, zmm1, [rbx+192]
> vaddpd zmm0, zmm0, zmm1
> ; and then the Horizontal sum
>
> >; Horizontal sum of zmm0
> >
> >vextractf64x4 ymm1, zmm0, 1
> >vaddpd ymm2, ymm1, ymm0
> >
> >vextractf64x2 xmm3, ymm2, 1
> >vaddpd ymm4, ymm3, ymm2
> >
> >vhaddpd xmm0, xmm4, xmm4
the simd instructions does also take a memory operand
I can du sum128 as
code asum128b
movsd [r13-0x8], xmm0
lea r13, [r13-0x8]
vmovapd zmm0, [rbx]
vaddpd zmm0, zmm0, [rbx+64]
vaddpd zmm0, zmm0, [rbx+128]
vaddpd zmm0, zmm0, [rbx+192]
vaddpd zmm0, zmm0, [rbx+256]
vaddpd zmm0, zmm0, [rbx+320]
vaddpd zmm0, zmm0, [rbx+384]
vaddpd zmm0, zmm0, [rbx+448]
vaddpd zmm0, zmm0, [rbx+512]
vaddpd zmm0, zmm0, [rbx+576]
vaddpd zmm0, zmm0, [rbx+640]
vaddpd zmm0, zmm0, [rbx+704]
vaddpd zmm0, zmm0, [rbx+768]
vaddpd zmm0, zmm0, [rbx+832]
vaddpd zmm0, zmm0, [rbx+896]
vaddpd zmm0, zmm0, [rbx+960]
Horizontal sum of zmm0
vextractf64x4 ymm1, zmm0, 1
vaddpd ymm2, ymm1, ymm0
vextractf64x2 xmm3, ymm2, 1
vaddpd ymm4, ymm3, ymm2
vpermilpd xmm5, xmm4, 1
vaddsd xmm0, xmm4, xmm5
ret
end-code
this compiles to 154 bytes and 25 instructions
The original sum128 is 2157 bytes and 513 instructions!
Yes the horizontal sum should just be done once.
I have only replaced sum128 with simd as a test.
Later I will do a complete example
This asum128b does not change the timing but reduces
the number of instructions
277,333,790 cycles:u
834,846,183 instructions:u # 3.01 insn per cycle
>
> Instead of doing the horizontal sum once for every sum128, it might be
> more efficient (assuming the whole thing is not
> cache-bandwidth-limited) to have the result of sum128 be a full SIMD
> width, and then add them up with vaddpd instead of addsd, and do the
> horizontal sum once in the end.
>
> But if the recursive part is to be programmed in Forth, we would need
> a way to represent a SIMD width of data in Forth, maybe with a SIMD
> stack. I see a few problems there:
>
> * What to do about the mask registers of AVX-512? In the RISC-V
> vector extension masks are stored in regular SIMD registers.
>
> * There is a trend visible in ARM SVE and the RISC-V Vector extension
> to have support for dealing with loops across longer vectors. Do we
> also need to support something like that.
>
> For the RISC-V vector extension, see
>
>
> One way to deal with all that would be to have a long-vector stack and
> have something like my vector wordset
> , where the sum of a vector
> would be a word that is implemented in some lower-level way (e.g.,
> assembly language); the sum of a vector is actually a planned, but not
> yet existing feature of this wordset.
>
> An advantage of having a (short) SIMD stack would be that one could
> use SIMD operations for other uses where the long-vector wordset looks
> too heavy-weight (or would need optimizations to get rid of the
> long-vector overhead). The question is if enough such uses exist to
> justify adding such a stack.
>
> - anton
I will take a look at your vector implementation and see if it can be used
in lxf64
BR
Peter
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