[PATCH] D19181: Map Attribute in the C API.

[James Y Knight via llvm-commits]

jyknight added a comment.

In http://reviews.llvm.org/D19181#413618, @whitequark wrote:

> @jyknight I strongly dislike exposing AttributeSet. What is the proposed usecase? FFI calls are expensive and using AttributeSet requires at least three operations (RMW) instead of one (Add) for the most common case (adding a single attribute). Further, AttributeSet is not easily interrogated; to get the full list of attributes, I propose (in the future) to add a function that returns an array of LLVMAttributeRef, which is again much nicer to bindings.


Why do you say adding a single attribute is the most common use-case? I'd expect the most common use to be to be creating a function definition/declaration/call instruction from scratch, with a given set of specified function/parameter/return-value attributes. Which is ideally suited for constructing an attribute set, and then calling a setter to place it onto the instruction. Why do you think RMW operations would be primary?

I'm not sure what you mean by not easily interrogated. In my proposed API, you'd have a loop, from 0 to what LLVMASNumAttributes returns, and can call LLVMASGetKindAtIndex and LLVMASGetStringKindAtIndex for each value, to retrieve them. That seems easy enough, and perfectly nice for bindings?

Actually, if we're really concerned about efficiency, we should also wrap AttrBuilder, and a function to construct an AttributeSet from an array of AttrBuilders, so that all the intermediate steps along the path towards building the AttributeSet you want in the end don't need to be memoized in the context.


http://reviews.llvm.org/D19181