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Newsgroups: comp.lang.ada
Date: Thu, 6 Jun 2019 23:21:08 -0700 (PDT)
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Subject: Re: Toy computational "benchmark" in Ada (new blog post)
From: David Trudgett <dktrudgett@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:56526
Date: 2019-06-06T23:21:08-07:00
List-Id: <comp.lang.ada>

Il giorno venerd=C3=AC 7 giugno 2019 15:57:36 UTC+10, Paul Rubin ha scritto=
:
>=20
> I think this is it below.  I don't understand why it's accumulating the
> values into a stack slot instead of a register, but I don't know the x86
> all that well.
>=20
>     .L17:
>             addq    $1, %rax
>     .LEHB4:
>             movq    416(%r12), %rdx
>             movsd   -8(%rdx,%rax,8), %xmm0
>     .LEHE4:
>             mulsd   %xmm0, %xmm0
>             cmpq    %rax, %rbp
>             addsd   8(%rsp), %xmm0
>             movsd   %xmm0, 8(%rsp)
>             jne     .L17
>             jmp     .L19

Instead, you should have something like:

.L5:
    movsd (%rax), %xmm0
    addq $8, %rax
    cmpq %rbx, %rax
    mulsd %xmm0, %xmm0
    addsd %xmm0, %xmm1
    jne .L5

It would appear you did not turn on optimisations since, as you noticed, it=
 is directly using the stack frame variable rather than keeping it in a reg=
ister.

Cheers,
David