https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43998
--- Comment #15 from Stas Sergeev ---
Btw, clang seems to allow same regs in input and clobber list.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=43998
Stas Sergeev changed:
What|Removed |Added
CC||stsp at users dot
sourceforge.net
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43998
Ilya Lesokhin ilya.lesokhin at gmail dot com changed:
What|Removed |Added
CC|
--- Comment #11 from socketpair at gmail dot com 2010-05-14 06:31 ---
Suppose this:
volatile int x;
asm(something::a (1))
x=1;
the compiler may think that something do not modify eax. So next assignment
may use eax ( mov eax, x ). So, it does not make sense to have it as a
clobber is
--- Comment #12 from ebotcazou at gcc dot gnu dot org 2010-05-14 07:10
---
the compiler may think that something do not modify eax. So next assignment
may use eax ( mov eax, x ). So, it does not make sense to have it as a
clobber is not correct. does not it ?
Andrew was saying that
--- Comment #10 from pinskia at gcc dot gnu dot org 2010-05-14 02:44
---
Because the way the constraints are implemented inside GCC, an input constraint
cannot overlap with a clobber. As input constraint can stay in the same
register across the inline-asm so it does not make sense to
--- Comment #1 from ubizjak at gmail dot com 2010-05-06 07:11 ---
You can use cpuid.h.
BTW: Please ask questions about using gcc in gcc-help@ or elsewhere.
Not a bug.
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ubizjak at gmail dot com changed:
What|Removed |Added
--- Comment #2 from jakub at gcc dot gnu dot org 2010-05-06 08:06 ---
To answer the exact question, yes, using a dummy variable as output (perhaps
with 1 instead of a for the matching input) is the right fix.
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43998
--- Comment #3 from socketpair at gmail dot com 2010-05-06 11:00 ---
Thanks alot, but I think it is bug in gcc inline assembler. I think I wrote
correct asm() line.
I know about cpuid.h
I listed this instruction just as example.
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socketpair at gmail dot com changed:
--- Comment #4 from rguenth at gcc dot gnu dot org 2010-05-06 11:31 ---
You can't at the same time force something into aregs and clobber them.
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rguenth at gcc dot gnu dot org changed:
What|Removed |Added
--- Comment #5 from socketpair at gmail dot com 2010-05-06 11:41 ---
Well, how to say that to compiler:
This instruction receives input in register eax, but after executing it, eax
value will be corrupted. I don't need this new value, but compiler should not
think that eax is
--- Comment #6 from hjl dot tools at gmail dot com 2010-05-06 13:09 ---
(In reply to comment #5)
Well, how to say that to compiler:
This instruction receives input in register eax, but after executing it, eax
value will be corrupted. I don't need this new value, but compiler
--- Comment #7 from socketpair at gmail dot com 2010-05-06 13:42 ---
Just make eax both input and output.
it's not optimal. gcc will try to preserve new eax value. So it will not use
eax register in next instructions. If eax is really need, it will save it in
esi, edi or so on - it's
--- Comment #8 from rguenth at gcc dot gnu dot org 2010-05-06 13:55 ---
(In reply to comment #7)
Just make eax both input and output.
it's not optimal. gcc will try to preserve new eax value. So it will not use
eax register in next instructions. If eax is really need, it will save
--- Comment #9 from socketpair at gmail dot com 2010-05-06 15:03 ---
Not if you make the output unused by not using it.
I do not understand why gcc distinguish between 'specifying register as output'
and 'specifying as clobbering'.
I always considered, that 'clobber list' specify list
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