port-alpha/60772: insane calling convention for uint32_t variables

["rokuyama.rk%gmail.com@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60772
>Category:       port-alpha
>Synopsis:       insane calling convention for uint32_t variables
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-alpha-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Sep 23 11:55:00 +0000 2026
>Originator:     Rin Okuyama
>Release:        11.99.8
>Organization:
Internet Initiative Japan Inc.
>Environment:
NetBSD ds10.local 11.99.8 NetBSD 11.99.8 (GENERIC-$Revision: 1.421 $) #0: Tue Sep 22 21:26:27 JST 2026  rin@sakaizumii.local:/home/rin/src/sys/arch/alpha/compile/obj.alpha-alpha/GENERIC alpha
>Description:
Due to "Digital UNIX: Calling Standard for Alpha Systems" Sec. 4.1.5,

https://archive.org/details/digital-unix-calling-standard/page/n1/mode/2up

when passing uint{8,16}_t and int{8,16}_t variables via registers,
these must be zero- and sign-extended, respectively. However, on the
other hand, {u,}int32_t must be sign-extended regardless of unsigned
or signed!

For our assembler-implemented functions, at least bswap32(3/9)
violates this rule, which results in part of GCC14 fallouts; GCC14
seems to utilize this calling convention for any optimization level
higher than -O0. If bswap32(3/9) is fixed, ipf and nfs ones of GCC14
fallouts are fixed.

However, unfortunately, other fallouts are not resolved. Especially,
GCC14 does not work natively as before...
>How-To-Repeat:
As the simplest test for this calling convention, compile this:

```
unsigned char u_char_func(void)
{
        return 0xffU;
}

unsigned short u_short_func(void)
{
        return 0xffffU;
}

unsigned int u_int_func(void)
{
        return 0xffffffffU;
}
```

Both GCC12 and GCC14 give:

```
0000000000000000 <u_char_func>:
   0:   ff 00 1f 20     lda     v0,255
   4:   01 80 fa 6b     ret

0000000000000008 <u_short_func>:
   8:   01 00 1f 24     ldah    v0,1
   c:   ff ff 00 20     lda     v0,-1(v0)
  10:   01 80 fa 6b     ret

0000000000000014 <u_int_func>:
  14:   ff ff 1f 20     lda     v0,-1
  18:   01 80 fa 6b     ret
```
>Fix:
At least, bswap32(3/9) must sign-extend its result before return.

Other assembler-implemented functions may be fixed similarly.