Re: question about compiling in a 64 bits system

[David Edelsohn <dje at watson dot ibm dot com>]

>>>>> Samuel Gaudard writes:

Samuel> The choice to compile in 64 bits comes from our customer even though we can
Samuel> advise him not to. Our priority on this application is performance and
Samuel> stability. I was wondering if using 32 bits binaries under a 64 bit os would
Samuel> slow down the execution (as the os deals with 64 bits blocks). If you have
Samuel> any idea about that.

	The performance impact depends on the application.  64 bit
applications double the size of some data and data structures, which will
slow down the application.  If the application requires 64 bit integer
computations, a 64 bit "long" or "long long" running in 64 bit mode will
be faster than a synthesized 64 bit "long long" running in 32 bit mode.
If the application needs to access more data than 32 bit addressing can
reference, it is better to map in all of the data as a 64 bit application
than to manually swap it into a 32 bit address space.  If those issues do
not apply, the application should be compiled as 32 bit.

	I do not understand the comment about 64 bit blocks.  64 bit AIX
kernels run 32 bit applications at full speed.

David

	P.S. Please use a different email account to contact the GCC
Project instead of sending email with boiler plate legal threats.