[Bug target/123631] Odd choice for vector constant materialization

[liuhongt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123631

--- Comment #1 from Hongtao Liu <liuhongt at gcc dot gnu.org> ---
It's done by r12-1958, it's better for dcache, but worse for icache, small
benchmark in the commit show broadcast from integer is slightly better than
constant pool, maybe we should make it as a u-arch specific tuning.