@mistydemeo @cliffrowley Sorry to revisit this (just woken up!) but I think `:haswell` is the right thing to test for on it's own, not `extmodel`. Have we actually seen any instances of Haswell people successfully compiling with SSSE3? 

If I'm right (and I'm no CPU expert and really struggling to find solid documentation) `extmodel` is an integer counting the chip revision with a microarchitecture generation (generations being Core, before that Netburst, before that P6..). My hunch for this is that 'Haswell' is the 4th revision of the Core microarchitecture, hence `extmodel` being 4. The point is some crazy old Pentium 4 might have `extmodel: 4` as well (I know that's only academic but it's all about code clarity!) 

`:haswell` captures exactly what we want - namely Rev. 4(a) of the Core Microarchitecture. If I'm right the second part of the conditional is redundant - all haswell machines *by definition* have extmodel of 4