[clang] [llvm] [SPIR-V] Add SPIR-V structurizer (PR #107408)

[Nathan Gauër via cfe-commits]

Keenuts wrote:

> > OpLoopMerge are taking BB operands, but verifier expected register operand.
> 
> Hopefully, the fix may be as simple as to change lib/Target/SPIRV/SPIRVInstrInfo.td line 620-621 `ID:$merge, ID:$continue` into `unknown:$merge, unknown:$continue` as in line 626 for OpBranch: `def OpBranch: Op<249, (outs), (ins unknown:$label), "OpBranch $label">;`

Oh thanks!
Turns out the barrier think can also be solved with just an `isBarrier = 1` in this td file.

https://github.com/llvm/llvm-project/pull/107408