http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39375
--- Comment #6 from Andrew Pinski pinskia at gcc dot gnu.org 2012-01-02
04:16:52 UTC ---
__asm__ (xxx : +X (sum));
Is most likely what you want to use. This says the sum might be clobbered but
it might not be as the same value is used if it was
--- Comment #4 from balrogg at gmail dot com 2009-03-16 16:53 ---
Reopening because
int params; __asm__ (xxx : =X (params));
and
int params[1]; __asm__ (xxx : =X (params[0]));
still produce different output in a way that is undocumented.
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balrogg at gmail dot com changed:
--- Comment #5 from pinskia at gcc dot gnu dot org 2009-03-16 17:02 ---
(In reply to comment #4)
Reopening because
int params; __asm__ (xxx : =X (params));
and
int params[1]; __asm__ (xxx : =X (params[0]));
still produce different output in a way that is undocumented.
How so? =X
--- Comment #3 from balrogg at gmail dot com 2009-03-06 10:34 ---
(In reply to comment #2)
You need to use a memory clobber instead. =X (params[1]) says to GCC
that the asm operand 0 should be stored to params[1], which it does
(it allocates %eax to it).
Note that =r doesn't
--- Comment #2 from rguenth at gcc dot gnu dot org 2009-03-05 10:42 ---
You need to use a memory clobber instead. =X (params[1]) says to GCC
that the asm operand 0 should be stored to params[1], which it does
(it allocates %eax to it). Note that plain use of %eax and %dx is a
bad idea
--- Comment #1 from balrogg at gmail dot com 2009-03-05 02:55 ---
(In reply to comment #0)
Similarly for =X but not =m or =r.
Rather, similarly for =g.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39375
