jayfoad wrote:
> > High level question: I don't understand why you call this a "gather"
> > operation. What do you mean by that? Isn't it semantically just a memcpy,
> > or a (global/buffer) load followed by a (LDS) store?
>
> The semantics of this operation (at least in the pre-gfx950 cases) are
>
> ```
> lds_load(vector globalAddr, scalar ldsAddr) {
> lds[ldsAddr + 4 * laneId] = global[globalAddr];
> }
> ```
>
> Note that your lane-varying global address can point all over memory, but
> that the values to written to LDS always go at base, base + 4 bytes, base + 8
> bytes, ... base + (wavesize - 1) * 4 bytes
>
> From where I'm standing, this is a gather
I see. The LDS part is doing "addtid" addressing. There are other instructions
that do this like `DS_LOAD_ADDTID_B32` and `GLOBAL_LOAD_ADDTID_B32` but I don't
think we have any codegen support for them.
I think we _could_ add the codegen support just by pattern-matching the
address, so `DS_LOAD_ADDTID_B32` would match something like `load ptr
addrspace(3) (constant_base + tid *4)`.
Then buffer-load-to-lds could be pattern-matched as a regular (fat pointer)
buffer load followed by an addtid-style LDS store, right? So no intrinsic is
really _needed_?
https://github.com/llvm/llvm-project/pull/137425
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