[clang] [HLSL] Add _m and _<numeric> based accessors to hlsl::matrix (PR #163220)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

> This needs a new AST node, it can't be done as the existing MatrixSubscriptExpr.
> 
> Consider this example:
> 
> ```
> export void fn() {
>     float2x2 M = {1,2,3,4};
>     float2 V = M._m00_m01; // produces a vector.
>     M._m10_m01 = 1.xx; // prodces a swizzled vector l-value!
> }
> ```
> 
> [Compiler Explorer](https://godbolt.org/z/ThPdvqbM3)

I was thinking this wouldn't be to hard to do by generating multiple MatrixSubscriptExpr(s) but your second point about retain source information to recreate this construct would still not be possible.

https://github.com/llvm/llvm-project/pull/163220