[Bug tree-optimization/101187] enhancement for vector logic right shift with constant bigger than element precision

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101187

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Do we really want that for vectors with int or larger elements though?
Shouldn't it be done for char/short elements only?
For non-common targets where char and/or short could have the same precision as
int, maybe best would be to do it only for elements with precision smaller than
precision of integer_type_node.
The advantage of doing it only for the char/short cases is that we can catch it
later in warnings, ubsan etc.
We should verify what we diagnose with ubsan if we say char/short element
vector shifts are well defined.
Also, we should do that only if the shift count is smaller than precision of
integer_type_node, i.e. optimize vector char >> 8 to >> 31 but not >> 32 and
more.
For signed vectors >> should be optimized to shift by element precision - 1.