Programming language ray tracing benchmarks project
I looked over the Common Lisp version at <a href="https:&#x2F;&#x2F;github.com&#x2F;niofis&#x2F;raybench&#x2F;blob&#x2F;master&#x2F;lisprb.lisp" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;niofis&#x2F;raybench&#x2F;blob&#x2F;master&#x2F;lisprb.lisp</a> and it&#x27;s… really bad, in a lot of ways.<p><pre><code>    (declaim (optimize (speed 3) (safety 0) (space 0) (debug 0) (compilation-speed 0)))
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<i>Never</i> use `(optimize (safety 0))` in SBCL — it throws safety <i>completely</i> out the window.  We&#x27;re talking C-levels of safety at that point.  Buffer overruns, the works.  It <i>might</i> buy you 10-20% speed, but it&#x27;s not worth it.  Lisp responsibly, use `(safety 1)`.<p><pre><code>    (defconstant WIDTH 1280)
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People generally name constants in CL with +plus-muffs+.  Naming them as uppercase doesn&#x27;t help because the reader uppercases symbol names by default when it reads.  So `(defconstant WIDTH ...)` means you can no longer have a variable named `width` (in the same package).<p><pre><code>    (defstruct (vec
                 (:conc-name v-)
                 (:constructor v-new (x y z))
                 (:type (vector float)))
      x y z)
</code></pre>
Using `:type (vector float)` here is trying to make things faster, but failing.  The type designator `float` covers <i>all</i> kinds of floats, e.g. both `single-float`s and `double-float`s in SBCL.  So all SBCL knows is that the struct contains some kind of float, and it can&#x27;t really do much with that information.  This means all the vector math functions below have to fall back to generic arithmetic, which is extremely slow.  SBCL even warns you about this when it&#x27;s compiling, thanks to the `(optimize (speed 3))` declaration, but I guess they ignored or didn&#x27;t understand those warnings.<p><pre><code>    (defconstant ZERO (v-new 0.0 0.0 0.0))
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This will cause problems because if it&#x27;s ever evaluated more than once it&#x27;ll try to redefine the constant to a new `vec` instance, which will not be `eql` to the old one.  Use `alexandria:define-constant` or just make it a global variable.<p>All the vector math functions are slow because they have no useful type information to work with:<p><pre><code>    (disassemble &#x27;v-add)
    ; disassembly for V-ADD
    ; Size: 160 bytes. Origin: #x52D799AF
    ; 9AF:       488B45F8         MOV RAX, [RBP-8]                ; no-arg-parsing entry point
    ; 9B3:       488B5001         MOV RDX, [RAX+1]
    ; 9B7:       488B45F0         MOV RAX, [RBP-16]
    ; 9BB:       488B7801         MOV RDI, [RAX+1]
    ; 9BF:       FF1425A8001052   CALL QWORD PTR [#x521000A8]     ; GENERIC-+
    ; 9C6:       488955E8         MOV [RBP-24], RDX
    ; 9CA:       488B45F8         MOV RAX, [RBP-8]
    ; 9CE:       488B5009         MOV RDX, [RAX+9]
    ; 9D2:       488B45F0         MOV RAX, [RBP-16]
    ; 9D6:       488B7809         MOV RDI, [RAX+9]
    ; 9DA:       FF1425A8001052   CALL QWORD PTR [#x521000A8]     ; GENERIC-+
    ; 9E1:       488BDA           MOV RBX, RDX
    ; 9E4:       488B45F8         MOV RAX, [RBP-8]
    ; 9E8:       488B5011         MOV RDX, [RAX+17]
    ; 9EC:       488B45F0         MOV RAX, [RBP-16]
    ; 9F0:       488B7811         MOV RDI, [RAX+17]
    ; 9F4:       48895DE0         MOV [RBP-32], RBX
    ; 9F8:       FF1425A8001052   CALL QWORD PTR [#x521000A8]     ; GENERIC-+
    ; 9FF:       488B5DE0         MOV RBX, [RBP-32]
    ; A03:       49896D40         MOV [R13+64], RBP               ; thread.pseudo-atomic-bits
    ; A07:       498B4520         MOV RAX, [R13+32]               ; thread.alloc-region
    ; A0B:       4C8D5830         LEA R11, [RAX+48]
    ; A0F:       4D3B5D28         CMP R11, [R13+40]
    ; A13:       772E             JNBE L2
    ; A15:       4D895D20         MOV [R13+32], R11               ; thread.alloc-region
    ; A19: L0:   C600D9           MOV BYTE PTR [RAX], -39
    ; A1C:       C6400806         MOV BYTE PTR [RAX+8], 6
    ; A20:       0C0F             OR AL, 15
    ; A22:       49316D40         XOR [R13+64], RBP               ; thread.pseudo-atomic-bits
    ; A26:       7402             JEQ L1
    ; A28:       CC09             BREAK 9                         ; pending interrupt trap
    ; A2A: L1:   488B4DE8         MOV RCX, [RBP-24]
    ; A2E:       48894801         MOV [RAX+1], RCX
    ; A32:       48895809         MOV [RAX+9], RBX
    ; A36:       48895011         MOV [RAX+17], RDX
    ; A3A:       488BD0           MOV RDX, RAX
    ; A3D:       488BE5           MOV RSP, RBP
    ; A40:       F8               CLC
    ; A41:       5D               POP RBP
    ; A42:       C3               RET
    ; A43: L2:   6A30             PUSH 48
    ; A45:       FF142520001052   CALL QWORD PTR [#x52100020]     ; ALLOC-TRAMP
    ; A4C:       58               POP RAX
    ; A4D:       EBCA             JMP L0
</code></pre>
If they had done the type declarations correctly, it would look more like this:<p><pre><code>    ; disassembly for V-ADD
    ; Size: 122 bytes. Origin: #x52C33A78
    ; 78:       F30F104A05       MOVSS XMM1, [RDX+5]              ; no-arg-parsing entry point
    ; 7D:       F30F105F05       MOVSS XMM3, [RDI+5]
    ; 82:       F30F58D9         ADDSS XMM3, XMM1
    ; 86:       F30F104A0D       MOVSS XMM1, [RDX+13]
    ; 8B:       F30F10670D       MOVSS XMM4, [RDI+13]
    ; 90:       F30F58E1         ADDSS XMM4, XMM1
    ; 94:       F30F104A15       MOVSS XMM1, [RDX+21]
    ; 99:       F30F105715       MOVSS XMM2, [RDI+21]
    ; 9E:       F30F58D1         ADDSS XMM2, XMM1
    ; A2:       49896D40         MOV [R13+64], RBP                ; thread.pseudo-atomic-bits
    ; A6:       498B4520         MOV RAX, [R13+32]                ; thread.alloc-region
    ; AA:       4C8D5820         LEA R11, [RAX+32]
    ; AE:       4D3B5D28         CMP R11, [R13+40]
    ; B2:       7734             JNBE L2
    ; B4:       4D895D20         MOV [R13+32], R11                ; thread.alloc-region
    ; B8: L0:   66C7005903       MOV WORD PTR [RAX], 857
    ; BD:       0C03             OR AL, 3
    ; BF:       49316D40         XOR [R13+64], RBP                ; thread.pseudo-atomic-bits
    ; C3:       7402             JEQ L1
    ; C5:       CC09             BREAK 9                          ; pending interrupt trap
    ; C7: L1:   C7400103024F50   MOV DWORD PTR [RAX+1], #x504F0203  ; #&lt;SB-KERNEL:LAYOUT for VEC {504F0203}&gt;
    ; CE:       F30F115805       MOVSS [RAX+5], XMM3
    ; D3:       F30F11600D       MOVSS [RAX+13], XMM4
    ; D8:       F30F115015       MOVSS [RAX+21], XMM2
    ; DD:       488BD0           MOV RDX, RAX
    ; E0:       488BE5           MOV RSP, RBP
    ; E3:       F8               CLC
    ; E4:       5D               POP RBP
    ; E5:       C3               RET
    ; E6:       CC0F             BREAK 15                         ; Invalid argument count trap
    ; E8: L2:   6A20             PUSH 32
    ; EA:       E8F1C64CFF       CALL #x521001E0                  ; ALLOC-TRAMP
    ; EF:       58               POP RAX
    ; F0:       EBC6             JMP L0
</code></pre>
The weirdness continues:<p><pre><code>    (defstruct (ray
                 (:conc-name ray-)
                 (:constructor ray-new (origin direction))
                 (:type vector))
      origin direction)
</code></pre>
The `:conc-name ray-` is useless, that&#x27;s the default conc-name.  And again with the `:type vector`… just make it a normal struct.  I was going to guess that they were doing it so they could use vector literals to specify the objects, but then why are they bothering to define a BOA constructor here?  And the slots are untyped, which, if you&#x27;re looking for speed, is not doing you any favors.<p>I took a few minutes over lunch to add some type declarations to the slots and important functions, inlined the math, cleaned up the broken indentation and naming issues:<p><a href="https:&#x2F;&#x2F;gist.github.com&#x2F;sjl&#x2F;005f27274adacd12ea2fc7f0b7200b80&#x2F;revisions?diff=split#diff-48e2da69300a7d7516647faf76fc0e20" rel="nofollow">https:&#x2F;&#x2F;gist.github.com&#x2F;sjl&#x2F;005f27274adacd12ea2fc7f0b7200b80...</a><p>The old version runs in 5m12s on my laptop, the new version runs in 58s.  So if we unscientifically extrapolate that to their 24m time, it puts it somewhere around 5m in their list.  This matches what I usually see from SBCL: for numeric-heavy code generic arithmetic is very slow, and some judicious use of type declarations can get you to within ~5-10x of C.  Getting more improvements beyond that can require really bonkers stuff that often isn&#x27;t worth it.