[mlir][llvm] Add support for importing masked intrinsics from LLVM IR.

[gysit]

Summary

The revision adds support for importing the masked load/store and
gather/scatter intrinsics from LLVM IR. To enable the import, the
revision also includes an extension of the mlirBuilder code generation
to support variadic arguments.

Depends on D136057

[ftynse]

mlir/lib/Target/LLVMIR/ConvertFromLLVMIR.cpp

247

Why does this have to materialize the vector?

mlir/tools/mlir-tblgen/LLVMIRConversionGen.cpp

80

Be aware that isVariableLength checks for both variadic and optional.

[gysit]

mlir/lib/Target/LLVMIR/ConvertFromLLVMIR.cpp

247

True I can return an ArrayRef.

mlir/tools/mlir-tblgen/LLVMIRConversionGen.cpp

80

I think we want to allow both at the moment but this is indeed a bit confusing given the name of the method. There are certain operations that use Optional<..> and certain others use Variadic<...>, which makes sense since the ReturnOp either takes 0 or 1 argument.

Would you prefer to support only Variadic operands here and handle Optional<...> in a different way. I can try how many things break if I am more restrictive.

[gysit]

Address comments.

[ftynse]

mlir/lib/Target/LLVMIR/ConvertFromLLVMIR.cpp

247

At this point, do you really need this helper? :)

mlir/tools/mlir-tblgen/LLVMIRConversionGen.cpp

80

Yes, I prefer with start with being more strict. Optional operands are more frequent than variadic ones and we would better be on the safe side given we are out of the tested path here.

[gysit]

mlir/lib/Target/LLVMIR/ConvertFromLLVMIR.cpp

247

I'll drop it yes.

[gysit]

Address comments.