[Bug c/115980] New: RISC-V: RVV dynamic-lmul test fail

[jiawei at iscas dot ac.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115980

            Bug ID: 115980
           Summary: RISC-V: RVV dynamic-lmul test fail
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jiawei at iscas dot ac.cn
  Target Milestone: ---

Current gcc trunk generated some unnecessary instructions with the case
gcc.dg/vect/costmodel/riscv/rvv/dynamic-lmul8-8.c

https://godbolt.org/z/5Tfqs9zqj