[boost] Default x86 instruction set

Subject: [boost] Default x86 instruction set
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2013-05-04 18:02:33

Hi,

I noticed that by default x86 32 bit builds are targeted for i386 (at least 
gcc toolset and its derivatives explicitly specify -march=i386 in the command 
line). Is there a reason to target for such an ancient instruction set by 
default?

Frankly, I'm not sure that the current Boost code would even run on a real 
80386, since there are at least quite a few places with atomic operations, 
which I think were not present on that CPU. Also, I would like to use cpuid 
safely in my library, and this operation appeared only in some i486 and all 
Pentiums, so I would basically target my code for Pentium at the very least.

But perhaps we could raise the default to Pentium Pro (i686)? Most Linux 
distributions already switched to this target for 32 bit builds because of 
availability of cmov instructions. Windows and OS X, I think, don't support 
older architectures either.