[Bug target/110751] RISC-V: Suport undefined value that allows VSETVL PASS use TA/MA

[juzhe.zhong at rivai dot ai via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110751

--- Comment #30 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
Hi.Richard.

I understand your conern:

If we are possible have this following possible rule to fold to ELSE value in
the future:

1. (cond_len all-false a b c len bias)
2. (cond_len any mask a b c len bias) (len + bias == 0)


I think it also can be easily fixed in the backend by ELSE_VALUE targethook.

We can return scalar 0 for else value only if (ops[0] != all false mask &&
LEN+BIAS ！= 0).

Am I right?

Thanks.