• lurker <a a.a> Mar 11 2011
• "Nick Sabalausky" <a a.a> Mar 11 2011
• Russel Winder <russel russel.org.uk> Mar 11 2011

lurker <a a.a> writes:

Jonathan M Davis Wrote:

 Now, assuming that all of that is taken care, if you're using a 32-bit binary
on 
 a 64-bit system, you're still going to be restricted on how much that program 
 can use. It doesn't use the native word size of the machine to do what it
does, 
 and in many cases, running a 32-bit program on a 64-bit machine is slower than 
 running a 64-bit version of that program on that machine (though that's going
to 
 vary from program to program, since there are  obviously quite a few factors 
 which affect efficiency).


The efficiency claim is true. 64-bit architures have much more registers. This
can effectively double the code's performance in most cases. Loads and stores
can also use full 64 bits of bandwidth instead of 32. Thus again twice as much
speed. In general if you worry about larger binary size, use UPX. Other than
that, 64 bit code outperforms the 32 bit. We want to keep the fastest compiler
title, right?

"Nick Sabalausky" <a a.a> writes:

"lurker" <a a.a> wrote in message news:ile2kg$2klo$1 digitalmars.com...
 Jonathan M Davis Wrote:

 Now, assuming that all of that is taken care, if you're using a 32-bit 
 binary on
 a 64-bit system, you're still going to be restricted on how much that 
 program
 can use. It doesn't use the native word size of the machine to do what it 
 does,
 and in many cases, running a 32-bit program on a 64-bit machine is slower 
 than
 running a 64-bit version of that program on that machine (though that's 
 going to
 vary from program to program, since there are  obviously quite a few 
 factors
 which affect efficiency).


 The efficiency claim is true. 64-bit architures have much more registers. 
 This can effectively double the code's performance in most cases. Loads 
 and stores can also use full 64 bits of bandwidth instead of 32. Thus 
 again twice as much speed. In general if you worry about larger binary 
 size, use UPX. Other than that, 64 bit code outperforms the 32 bit. We 
 want to keep the fastest compiler title, right?


OTOH, 32-bit code on 64-bit already vastly outperforms 32-bit code on a 
32-bit machine anyway.

Russel Winder <russel russel.org.uk> writes:

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On Fri, 2011-03-11 at 16:02 -0500, lurker wrote:
[ . . . ]
 The efficiency claim is true. 64-bit architures have much more
 registers. This can effectively double the code's performance in most
 cases. Loads and stores can also use full 64 bits of bandwidth instead
 of 32. Thus again twice as much speed. In general if you worry about
 larger binary size, use UPX. Other than that, 64 bit code outperforms
 the 32 bit. We want to keep the fastest compiler title, right?


There are a large number of assumptions in the claim of "twice as much
speed".  All the AMD64 registers and ALUs are 64-bit wide but are all
the caches?  Are all the buses to memory?  Are all the memory
structures?  Is the clock speed the same?  Are all the components
clocked in the same way?

Has anyone got actual experimental data?  Is there a benchmark suite?

My preference for a 64-bit DMD relate to simplicity of use on Debian and
Ubuntu where the packaging is far simpler if 64-bit executables are used
throughout -- if those executables are dynamically linked.  If they are
statically linked there is not the same issues, but then physical size
of executable becomes an issue.

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