[Bug target/113240] New: Use wrong rule to pass fixed-length(size<=2*XLEN) vector argument

[lehua.ding at rivai dot ai via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113240

            Bug ID: 113240
           Summary: Use wrong rule to pass fixed-length(size<=2*XLEN)
                    vector argument
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: lehua.ding at rivai dot ai
  Target Milestone: ---

According to a recent proposal
(https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/416), GCC
incorrectly uses references when passing fixed-length vector arguments with
size less than or equal to 2*VLEN instead of scalar registers for passing.
Reproduced online: https://godbolt.org/z/3ooovcz7c

C Code:
```
#include <stdint.h>

typedef int v4si __attribute__ ((vector_size (16)));

v4si foo (v4si a, v4si b)
{
  v4si c = a + b;
  return c;
}
```

Asm:
```
foo:
        vsetivli        zero,4,e32,m1,ta,ma
        vle32.v v1,0(a1)
        vle32.v v2,0(a2)
        vadd.vv v1,v1,v2
        vse32.v v1,0(a0)
        ret
```