[llvm] [DXIL] Add DXIL SubArch to correspond to version number (PR #89125)

[Damyan Pepper via llvm-commits]

damyanp wrote:

> > What's the plan for when a subarch isn't specified (ie, `dxil-pc-shadermodel-6.0`)? 
> I propose defaulting to version 1.0 when SubArch is not explicitly specified.

So if I specify `dxil-pc-shadermodel-6.8` then the SubArch will be `DXILSubArch_v10`?  Will that work out ok everywhere?


https://github.com/llvm/llvm-project/pull/89125