Compiling GCC for different x86 CPU generation

[Andrew Janke]

On 7/24/18 6:10 AM, Xi Ruoyao wrote:
> 
> I agree with Marc that the problem is likely to be in MPC/GMP/MPFR.
> Use contrib/download_prerequistes to get the source code of them,
> and try to compile GCC with --enable-bootstrap.

Found it!

Your suspicions were correct: it was in MPC.

I wasn't able to get debug symbols working (apparently they're hard on 
macOS), but I found this program to dump instruction set extension names 
- https://github.com/pkgw/elfx86exts - and ran it on gfortran and those 
libraries, and that BMI2 MULX instruction showed up in libgmp.

$ elfx86exts libgmp.dylib
MODE64 (push)
SSE1 (xorps)
SSE2 (ucomisd)
CMOV (cmove)
BMI2 (mulx)

Rebuilding GMP for Core2 fixed the issue. This wasn't a gfortran/GCC 
build problem after all.

Thank you for your help! This discussion was very useful.

Cheers,
Andrew