This is the mail archive of the
gcc-help@gcc.gnu.org
mailing list for the GCC project.
i686 architecture behaviour in gcc
- From: David Fernandez <dfernandez at cct dot co dot uk>
- To: gcc-help at gcc dot gnu dot org
- Date: Tue, 21 Feb 2006 17:08:31 +0000
- Subject: i686 architecture behaviour in gcc
Hi there,
Can anyone explain why has been chosen that -march=i686 makes the
compiler change the normal behaviour, and zero-expand unsigned short
parameters into 32-bit registers by all means?
E.g.
void __attribute(( regparm(2) )) myoutl( d, p )
{
asm(" outl %0,(%w1) \n"
:
: "a" (d), "d" (p) );
}
assembled with
gcc -Os -fomit-frame-pointer -march=i586 ...
gives us
outl %eax,(%dx)
ret
but changing "-march=i686" gives us
movzwl %dx,%edx
outl %eax,(%dx)
ret
Is it a bug, or had any developer a good reason to do so?
David