[Bug target/92760] [10 regression] several vector test cases fail on power 7 after r278800

[linkw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92760

Kewen Lin <linkw at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |segher at gcc dot gnu.org

--- Comment #1 from Kewen Lin <linkw at gcc dot gnu.org> ---
This issue exposes one interesting point, ISA 2.06 (Power7) introduces partial
support on vector doubleword, so we can exploit them in vectorization, but more
instructions support on vector doubleword origins from ISA 2.07 (Power8),
that's why we set rs6000_vector_unit[V2DImode] only under VECTOR_P8_VECTOR.

To be consistent and allow us to use limited doubleword vector support, I'd
like to update it to check VECTOR_MEM_NONE_P is none as well.