[llvm] [LLVM][CodeGen][SPIRV] Match NULL splat to OpConstantNull. (PR #201313)

[Vyacheslav Levytskyy via llvm-commits]

VyacheslavLevytskyy wrote:

lgtm, but we need feedback about graphics flavour behaviour: there are a lot of lines `bool ZeroAsNull = !STI.isShader();` in SPIRVInstructionSelector.cpp so the question is whether Vulkan needs a guard here or not

https://github.com/llvm/llvm-project/pull/201313