Add speculatable attribute

[vchuravy]

Noticed that this was missing while experimenting with llvm-dialects.

Is there already an interface for specifing return attributes / per-argument interfaces?

[nhaehnle]

Thanks!

Is there already an interface for specifing return attributes / per-argument interfaces?

No. Look how llvm_dialects::genDialectDefs invokes LlvmAttributeTrait::addAttribute to generate the code that adds attributes to attribute lists. We'd have to extend both the invocation site to support adding attributes at indices other than FunctionIndex, and the Trait hierarchy to represent attributes in argument or return position.

Perhaps an LlvmArgEnumAttributeTrait class in TableGen that allows defining

def NoCaptureArg<int idx> : LlvmArgEnumAttributeTrait<idx, "NoCapture">;
// etc.

and similar for return attributes.

[nhaehnle]

Thinking about this a bit more, working with indices when defining operations is a bit clunky. Perhaps the TableGen should look like this:

def FooOp : ... {
  let arguments = (ins Ptr:$ptr);
  let results = (outs Ptr:$result);

  let value_traits = [
    (ReadOnly $ptr),
    (NoCapture $ptr),
    (NonNull $result),
  ];
}

We could then potentially re-use the LlvmEnumAttributeTrait TableGen class, but perhaps add a field that indicates which positions the attribute can appear in.