llvm dev - Dec 2020 - GISel using deprecated vector_extract for G_EXTRACT_VECTOR_ELT mapping

According to code comment the definition of vector_extract has
been deprecated for ~5 years (at least since Dec 11, 2015).

Seems like some targets still are using it, and even the GlobalISel
implementation is supporting this deprecated functionality by
adding a mapping between G_EXTRACT_VECTOR_ELT and vector_extract
in SlectionDAGCompat.td.

My target is not using the deprecated vector_extract, and it is using
the preferred extractelt definition instead in tablegen patterns.

The problem is that there is no similar mapping between
extractelt and G_EXTRACT_VECTOR_ELT.

Is it allowed to have several GINodeEquiv statements, mapping the
same GISel instruction to different SDNodes?

(i.e. would it be wrong to also add a mapping between
G_EXTRACT_VECTOR_ELT and extractelt)

Or should we stop using the deprecated nodes in GISel mappings?

(then I assume someone need to finalize the work of getting rid
of vector_extract, at least in targets that support GISel, but
after 5 years I think it is about time to either remove the
deprecated definition or replace the "deprecated" comment with
something that explains why we need both vector_extract and
extractelt)


PS. The above questions also apply to vector_insert vs insertelt.

/Björn

> On Dec 9, 2020, at 06:51, Björn Pettersson A via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> According to code comment the definition of vector_extract has
> been deprecated for ~5 years (at least since Dec 11, 2015).
> 
> Seems like some targets still are using it, and even the GlobalISel
> implementation is supporting this deprecated functionality by
> adding a mapping between G_EXTRACT_VECTOR_ELT and vector_extract
> in SlectionDAGCompat.td.
GlobalISel only supports them because the first targets implemented used
vector_extract
> My target is not using the deprecated vector_extract, and it is using
> the preferred extractelt definition instead in tablegen patterns.
> 
> The problem is that there is no similar mapping between
> extractelt and G_EXTRACT_VECTOR_ELT.
> 
> Is it allowed to have several GINodeEquiv statements, mapping the
> same GISel instruction to different SDNodes?
> 
> (i.e. would it be wrong to also add a mapping between
> G_EXTRACT_VECTOR_ELT and extractelt)
Off-hand, I don't think there's a reason that would be a problem so long
as you only have one or the other in your target. The GINodeEquiv relations are
there to map operators in the rule like vector_extract/extractelt to their GISel
counterparts so it can generate code in GISel terms. If you somehow have both
and they have overlapping rules then it would be undefined which rule is used.
> Or should we stop using the deprecated nodes in GISel mappings?
> 
> (then I assume someone need to finalize the work of getting rid
> of vector_extract, at least in targets that support GISel, but
> after 5 years I think it is about time to either remove the
> deprecated definition or replace the "deprecated" comment with
> something that explains why we need both vector_extract and
> extractelt)
> 
> 
> PS. The above questions also apply to vector_insert vs insertelt.
> 
> /Björn
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