Increasing D Compiler Speed by Over 75%

[Rainer Schuetze]

On 02.08.2013 10:24, Walter Bright wrote:
> On 8/2/2013 12:57 AM, Rainer Schuetze wrote:
>>> http://www.digitalmars.com/download/freecompiler.html
>>
>> Although my laptop got quite a bit faster overnight (I guess it was
>> throttled
>> for some reason yesterday), relative results don't change:
>>
>> std.algorithm -main -unittest
>>
>> dmc85?: 12.5 sec
>> dmc857: 12.5 sec
>> msc: 7 sec
>>
>> BTW: I usually use VS2008, but now also tried VS2010 - no difference.
>
> The two dmc times shouldn't be the same. I see a definite improvement.
> Disassemble aav.obj, and look at the function aaGetRvalue. It should
> look like this:

My disassembly looks exactly the same. I don't think that a single div 
operation in a rather long function has a lot of impact on modern 
processors. I'm running an i7, according to the instruction tables by 
Agner Fog, the div has latency of 17-28 cycles and a reciprocal 
throughput of 7-17 cycles. If I estimate the latency of the asm snippet, 
I also get 16 cycles. And that doesn't take the additional tests and 
jumps into consideration.

======== note this section does not have a div instruction in it 
==============
                 mov     EAX,EBX
                 mov     EDX,08421085h   ; latency 3
                 mov     ECX,EBX
                 mul     EDX             ; latency 5
                 mov     EAX,ECX
                 sub     EAX,EDX         ; latency 1
                 shr     EAX,1           ; latency 1
                 lea     EDX,[EAX][EDX]  ; latency 1
                 shr     EDX,4           ; latency 1
                 imul    EAX,EDX,01Fh    ; latency 3
                 sub     ECX,EAX         ; latency 1
                 mov     ESI,ECX
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