Building GMP 6.0 for Ivy Bridge

[Victor Shoup]

Hi!

I'm building GMP on an Ivy Bridge based machine
running Cent OS.  My compiler is GCC v4.9.2.
I'd like to make sure I get the best possible build
for this machine.

According to lscpu:

Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz

which is Ivy Bridge, AFAIK.

According to lsb_release -a:

LSB Version:	:core-4.1-amd64:core-4.1-noarch:cxx-4.1-amd64:cxx-4.1-noarch:desktop-4.1-amd64:desktop-4.1-noarch:languages-4.1-amd64:languages-4.1-noarch:printing-4.1-amd64:printing-4.1-noarch
Distributor ID:	CentOS
Description:	CentOS Linux release 7.1.1503 (Core) 
Release:	7.1.1503
Codename:	Core

Now, I've built GMP successfully, but looking at config.log,
there is nothing there to suggest that it knows what kind of machine
this is.  I see this, for example in config.log:


## ----------- ##
## Core tests. ##
## ----------- ##

configure:3040: checking build system type
configure:3054: result: x86_64-unknown-linux-gnu
configure:3074: checking host system type
configure:3087: result: x86_64-unknown-linux-gnu

And the output of config.guess is:

x86_64-unknown-linux-gnu

So, does anyone know:

(1) how can I tell if GMP is actually using the code that is
    specialized for Ivy Bridge?

(2) if my current build is not properly specialized, can I expect
    a significant speedup (e.g., for very large muls) if I get it 
    built properly specialized?

(3) how do I go about building it properly specialized?

Thanks for your help!
-Victor