[LLVMdev] llvm::Triple support for haswell-enabled x86_64

[Jim Grosbach]

> On Aug 20, 2014, at 9:37 AM, Reid Kleckner <rnk at google.com> wrote:
> 
> On Tue, Aug 19, 2014 at 10:37 PM, Chandler Carruth <chandlerc at google.com> wrote:
> 
> On Tue, Aug 19, 2014 at 5:05 PM, Jim Grosbach <grosbach at apple.com> wrote:
> Note that it’s not exactly equivalent to enabling -march=core-avx2. It’s really close, but not 100% the same.
> 
> What is the difference? and why? It seems really confusing to have this divergence, or to be unable to replicate the *exact* behavior of this (very weird, and IMO *bad* triple) with the standard triple of 'x86_64-...' and an '-march' flag.
> 
> It just seems like a reinvention of i386, i486, and iN86, probably for all of the same reasons. If you can encode all the important things in the triple, you can have different library directories for distributions, etc. 

There’s a few more subtleties, but that’s a reasonable analogy. While the sub-arch is related to a -march= setting, it is very definitely not the same thing. It’s not even just the sub-arch. Consider, for example, that “thumb” and “arm” have separate top-level triple values.

Yes, this whole system of how the arch and sub arch triple stuff works is brittle and ugly. Now that we have module level attributes and such, it’s probably possible to design something more sane. It’s debatable whether it’s worth the effort, but it’s possible.
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