[Bug c++/115325] New: RVV vmulh and vmulhu unknown without -march, but vmul is known

[Bug c++/115325] New: RVV vmulh and vmulhu unknown without -march, but vmul is known

[jan.wassenberg at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115325

            Bug ID: 115325
           Summary: RVV vmulh and vmulhu unknown without -march, but vmul
                    is known
           Product: gcc
           Version: 14.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jan.wassenberg at gmail dot com
  Target Milestone: ---

To allow runtime dispatch (detecting at runtime whether V is available), we
would like to compile without -march=.

In GCC 13 for RVV this raised an #error. Looks like there has been progress in
GCC 14, no more #error in riscv_vector.h, but there is a strange difference
between vmulh and vmulh. Repro: https://gcc.godbolt.org/z/9PjEajq7r

When compiling without -march, vmul is at least known, though we get 
"return type 'vint64m1_t' requires the V ISA extension". We are almost but not
entirely able to get rid of this by using vectors only within the function:
https://gcc.godbolt.org/z/W74j7nzvs
(This is also blocking runtime dispatch.)

When compiling without -march, the situation worsens: changing vmul to vmulh
results in "error: '__riscv_vmulh_vv_i64m1' was not declared in this scope; did
you mean '__riscv_vmul_vv_i64m1'?".

[Bug target/115325] RVV vmulh and vmulhu unknown without -march, but vmul is known

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115325

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The correct way of doing this is to use `pragma GCC target` but that is not
supported on riscv yet ...

[Bug target/115325] RVV vmulh and vmulhu unknown without -march, but vmul is known

[jan.wassenberg at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115325

--- Comment #2 from Jan Wassenberg <jan.wassenberg at gmail dot com> ---
Thanks, we are equipped to use pragma GCC target as soon as it is ready. Is
there any bug/tracker to which I could subscribe for updates on that?