Questions about march/mcpu/mattr and good generic defaults

bearophile bearophileHUGS at
Thu Dec 19 15:55:06 PST 2013

Mikko Ronkainen:

> Do -m32/m64 just mean -march=x86/x86-64?


> To create a generic 32-bit program, are these sane choices:
> -m32 -mcpu=i686 -mattr=sse2 ?

I think sse2 is active on default on Windows.

> I see 100% performance increase between sse2 and sse/none. 
> Optimizer seems to like quite a lot.

Right, I think LLVM used to produce SSE code before being able to 
produce the older stack-based FP code. So LLVM likes SSE code a 
lot. It's the standard.


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