We already do:
concat_vectors(scalar, undef) -> scalar_to_vector(scalar)
When the scalar is legal.
When it's not, but is a truncated legal scalar, we can also do:
concat_vectors(trunc(scalar), undef) -> scalar_to_vector(scalar)
Which is equivalent, since the upper lanes are undef anyway.
While there, teach the combine to look at more than 2 operands.
Differential Revision: http://reviews.llvm.org/D8883
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234530 91177308-0d34-0410-b5e6-96231b3b80d8
Optimize concat_vectors of truncated vectors, where the intermediate
type is illegal, to avoid said illegality, e.g.,
(v4i16 (concat_vectors (v2i16 (truncate (v2i64))),
(v2i16 (truncate (v2i64)))))
->
(v4i16 (truncate (v4i32 (concat_vectors (v2i32 (truncate (v2i64))),
(v2i32 (truncate (v2i64)))))))
This isn't really target-specific, and, as such, would best go in the
DAGCombiner. However, ISD::TRUNCATE legality isn't keyed on both input
and result type, so we might generate worse code when we don't know
better. On AArch64 we know it's fine for v2i64->v4i16 and v4i32->v8i8.
rdar://20022387
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232459 91177308-0d34-0410-b5e6-96231b3b80d8
