[Bug target/95488] Suboptimal multiplication codegen for v16qi

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95488

--- Comment #3 from Hongtao.liu <crazylht at gmail dot com> ---
(In reply to Richard Biener from comment #2)
> (In reply to Hongtao.liu from comment #1)
> > I think it's this TYPE_SIGN (TREE_TYPE (REG_EXPR (op1))).
> 
> That's not reliable.  Mutliplication shouldn't care about sign?

We need to extend v16qi to v16hi first, extension does care about sign.