[llvm-dev] Alignment parameter attributes

Doerfert, Johannes via llvm-dev llvm-dev at lists.llvm.org
Tue Jan 14 12:57:10 PST 2020

On 01/14, Greene, David via llvm-dev wrote:
> I have a question about how to communicate alignment via function
> parameters.  The IR supports an attribute specifying the alignment of a
> pointer parameter:
> define void @func(double* noalias align 64 %p)
> This says that %p is 64-byte aligned.  Great!
> Is there any way to convey the alignment of a pointer pointed to by a **
> argument?  I'd like something like this:
> define void @func(double* align 64 * noalias %p)
> Or even this to add a noalias attribute:
> define void @func(double* noalias align 64 * noalias %p)
> I don't think either of these is legal today.
> Has anyone else run into this need?  If so, any advice would be much
> appreciated!

If you have this knowledge during code generation you can associate
align metadata to the loads from %p.

We could use a custom tag on `llvm.assume`, as an extension of
https://reviews.llvm.org/D72475, but that is not yet implemented.

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