J. Scott Kasten wrote:
[snip]
> > I don't know how file detects this, but at least current CVS gas
> > does not set the appropriate flag in the object file header.
>
> Gas does not apply here. We're talking about gcc running under Irix with
> the native as and ld tools. I'm using gcc-2.91.66 (egcs-1.1.2),
> gcc-2.95.2, MipsPro 7.30 as and ld.
Sorry, I have missed this.
> > > >
> > > > Run:
> > > >
> > > > sizeof(int) = 8, sizeof(*) = 8
> > ^ ^
> > This should be both 4, I assume this happened due to -mint64.
>
> Not totally. -mips3 generates values of 4 and 8. The -mint64 takes it to
> 8 and 8. If I just invoke gcc with no -m flags, it does produce 4 and 4.
n32 ABI uses sizeof(void *) == 4, so something went wrong here.
[snip]
> Just for kicks, instead of *j = 10, which is trivial, I picked a true 64
> bit constant:
Are you a telepathic? :-)
> sd $2,40($fp)
> ld $2,40($fp)
> dli $3,0x807060504030201
> sd $3,0($2)
> ld $2,32($fp)
> daddu $3,$2,1
> sd $3,32($fp)
> ld $2,40($fp)
>
>
> 100012b0: ffc20028 sd $v0,40($s8)
> 100012b4: dfc20028 ld $v0,40($s8)
> 100012b8: 3c030807 lui $v1,0x807
> 100012bc: 34630605 ori $v1,$v1,0x605
> 100012c0: 00031c38 dsll $v1,$v1,0x10
> 100012c4: 34630403 ori $v1,$v1,0x403
> 100012c8: 00031c38 dsll $v1,$v1,0x10
> 100012cc: 34630201 ori $v1,$v1,0x201
> 100012d0: fc430000 sd $v1,0($v0)
> 100012d4: dfc20020 ld $v0,32($s8)
> 100012d8: 64430001 daddiu $v1,$v0,1
> 100012dc: ffc30020 sd $v1,32($s8)
> 100012e0: dfc20028 ld $v0,40($s8)
>
> Ouch that's a painfull load. It's interesting that in both cases, it
> effectively makes the constant load a 16 bit operation, does the math 64
> bit, and stores 64 bit.
Loading constants via 16bit immediates is normal and the fastest
way on MIPS. The really interesting part is that the load avoids
clobbering $at. For superscalar processors it's faster to do e.g.
lui $v1,0x807
lui $at,$at,0x403
ori $v1,$v1,0x605
ori $at,$at,0x201
dsll32 $v1,$v1,0x0
or $v1,$v1,$at
with a critical path length of 4 instead of 6.
Thiemo
