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<p>Hi Nataraj<br>
</p>
<p>Which processor is that run on? (although too close to call, it
implies LEA has a latency of 2 in that case)<br>
</p>
<p>Kit<br>
</p>
<div class="moz-cite-prefix">On 08/10/2023 14:06, Nataraj S Narayan
via fpc-devel wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAK8HZO+JFu=UoV7f9qW+rURFz7CxmYy=A9rKx1rCjhSrTch=XA@mail.gmail.com">
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<div>Hi</div>
<div><br>
</div>
<div>[nataraj@dflyHP ~]$ fpc ttt.pas</div>
Free Pascal Compiler version 3.2.2 [2023/07/04] for x86_64<br>
Copyright (c) 1993-2021 by Florian Klaempfl and others<br>
Target OS: DragonFly for x86-64<br>
Compiling ttt.pas<br>
Linking ttt<br>
/usr/local/bin/ld.bfd: warning:
/usr/local/lib/fpc/3.2.2/units/x86_64-dragonfly/rtl/prt0.o:
missing .note.GNU-stack section implies executable stack<br>
/usr/local/bin/ld.bfd: NOTE: This behaviour is deprecated and
will be removed in a future version of the linker<br>
121 lines compiled, 14.9 sec<br>
[nataraj@dflyHP ~]$ ./ttt <br>
Pascal control case: 6.7 ns/call<br>
Using LEA instruction: 4.2 ns/call<br>
Using ADD instructions: 4.0 ns/call<br>
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data-smartmail="gmail_signature">
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<div dir="ltr"><br>
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<div dir="ltr"><br>
</div>
<div dir="ltr">Nataraj S Narayan
<div>Synergy Info Systems</div>
<div>Software & Technology Consultants</div>
<div>Ettumanoor, INDIA</div>
<div>Ph:+91 9443211326</div>
</div>
</div>
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<br>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Sat, Oct 7, 2023 at 9:39 PM
J. Gareth Moreton via fpc-devel <<a
href="mailto:fpc-devel@lists.freepascal.org"
moz-do-not-send="true" class="moz-txt-link-freetext">fpc-devel@lists.freepascal.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">That's
interesting; I am interested to see the assembly output for
the <br>
Pascal control cases. As for the 64-bit version, that was my
fault <br>
since the assembly language is for Microsoft's ABI rather than
the <br>
System V ABI, so it was checking a register with an undefined
value. <br>
Find attached the fixed test.<br>
<br>
Kit<br>
<br>
P.S. Results on my Intel(R) Core(TM) i7-10750H<br>
<br>
Pascal control case: 2.0 ns/call<br>
Using LEA instruction: 1.7 ns/call<br>
Using ADD instructions: 1.3 ns/call<br>
<br>
On 07/10/2023 16:51, Tomas Hajny via fpc-devel wrote:<br>
> On 2023-10-07 03:57, J. Gareth Moreton via fpc-devel
wrote:<br>
><br>
><br>
> Hi Kit,<br>
><br>
>> Do you think this should suffice? Originally it ran
for 1,000,000<br>
>> repetitions but I fear that will take way too long on
a 486, so I<br>
>> reduced it to 10,000.<br>
><br>
> OK, I tried it now. First of all, after turning on the
old machine, I <br>
> realized that it wasn't Intel but AMD 486 DX4 - sorry for
my bad <br>
> memory. :-( I compiled and ran the test under OS/2 there
(I was too <br>
> lazy to boot it to DOS ;-) ), but I assume that it
shouldn't make any <br>
> substantial difference. The ADD and LEA results were
basically the <br>
> same there, both around 100 ns / call. The Pascal result
was around <br>
> twice as long. Interestingly, the Pascal result for FPC
3.2.2 was <br>
> around 10% longer than the same source compiled with FPC
2.0.3 (the <br>
> assembler versions were obviously the same for both FPC
versions; I <br>
> tried compiling it also with FPC 1.0.10 and the assembler
versions <br>
> were more than three times slower due to missing support
for the <br>
> nostackframe directive).<br>
><br>
> I tested it under the AMD Athlon 1 GHz machine as well
and again, the <br>
> results for LEA and ADD are basically equal (both 3.1
ns/call) and the <br>
> result for Pascal slightly more than twice (7.3 ns/call).
However, <br>
> rather surprisingly for me, the overall test run was
_much_ longer <br>
> there?! Finally, I tried compiling the test on a 64-bit
machine (AMD <br>
> A9-9425) with Linux (compiled for 64-bits with FPC 3.2.3
compiled from <br>
> a fresh 3.2 branch). The Pascal version shows about 4
ns/call, but the <br>
> assembler version runs forever - well, certainly much
longer than my <br>
> patience lasts. I haven't tried to analyze the reasons,
but that's <br>
> what I get.<br>
><br>
> Tomas<br>
><br>
><br>
><br>
>><br>
>> On 03/10/2023 06:30, Tomas Hajny via fpc-devel wrote:<br>
>>> On October 3, 2023 03:32:34 +0200, "J. Gareth
Moreton via fpc-devel" <br>
>>> <<a
href="mailto:fpc-devel@lists.freepascal.org" target="_blank"
moz-do-not-send="true" class="moz-txt-link-freetext">fpc-devel@lists.freepascal.org</a>>
wrote:<br>
>>><br>
>>><br>
>>> Hii Kit,<br>
>>><br>
>>>> This is mainly to Florian, but also to anyone
else who can answer <br>
>>>> the question - at which point did a complex
LEA instruction (using <br>
>>>> all three input operands and some other
specific circumstances) get <br>
>>>> slow? Preliminary research suggests the 486
was when it gained <br>
>>>> extra latency, and then Sandy Bridge when it
got particularly bad. <br>
>>>> Icy Lake seems to be the architecture where
faster LEA instructions <br>
>>>> are reintroduced, but I'm not sure about AMD
processors.<br>
>>> I cannot answer your question, but if you prepare
a test program, I <br>
>>> can run it on an Intel 486 DX2 100 Mhz and AMD
Athlon 1 GHz machines <br>
>>> if it helps you in any way (at least I hope the
486 DX2 machine <br>
>>> should be still able to start ;-) ).<br>
>>><br>
>>> Tomas<br>
>>><br>
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