[PATCH] D71215: [AArch64][SVE] Add patterns for unpredicated load/store to frame-indices.

[Sander de Smalen via Phabricator via llvm-commits]

sdesmalen marked an inline comment as done.
sdesmalen added inline comments.


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Comment at: llvm/lib/Target/AArch64/AArch64SVEInstrInfo.td:1267
+  defm Pat_Load_P4  : unpred_load_predicate<nxv4i1, LDR_PXI>;
+  defm Pat_Load_P2  : unpred_load_predicate<nxv2i1, LDR_PXI>;
 }
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sdesmalen wrote:
> efriedma wrote:
> > nxv2i1 has the same memory layout as nxv16i1?  I guess that makes sense given the available instructions.  We might need to modify the datalayout to make that work properly; I think, without any explicit guidance from the layout string, it will assume a nxv2i1 load reads "vscale" bytes, not "vscale * 2" bytes.
> > 
> > Not something to change in this patch, of course.
> DataLayout assumes that each boolean has a memory size of `i8` as each predicate needs to be individually addressable, which leads to `storesize(<vscale x 2 x i1>) == storesize(<vscale x 2 x i8>)`.
> This also means that alloca's of predicates may allocate too much stack space depending on the number of elements. The generated code is correct because all the offsets scale accordingly; you can see this for example in `spill_nxv16i1` and `spill_nxv2i1`. The former (nxv16i1) allocates the sizeof two nxv16i8 vectors and loads the second predicate from offset `8 [* sizeof(predicate)]`, where the latter allocates the sizeof one nxv16i8 vector, and loads the second predicate from offset `2 [* sizeof(predicate)]`. (`sizeof(predicate) = (vscale * 2 bytes)`)
> This is different from spills introduced by e.g. the register allocator, where LLVM allocates space for the size of an (otherwise opaque) predicate register, set to 2 bytes.
I should probably also point out that there is no other interface for users to read/write these predicates other than through `svbool_t`, which is an opaque type, so I don't think there is any need to expand the store of `nxv16i1` to a store of `nxv16i8`.


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  https://reviews.llvm.org/D71215/new/

https://reviews.llvm.org/D71215