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* [Bug inline-asm/99259] New: aarch64 inline asm: miscompilation depending on function parameters order
@ 2021-02-24 19:59 jacob.benoit.1 at gmail dot com
2021-02-24 20:01 ` [Bug inline-asm/99259] " jacob.benoit.1 at gmail dot com
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: jacob.benoit.1 at gmail dot com @ 2021-02-24 19:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99259
Bug ID: 99259
Summary: aarch64 inline asm: miscompilation depending on
function parameters order
Product: gcc
Version: 10.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: inline-asm
Assignee: unassigned at gcc dot gnu.org
Reporter: jacob.benoit.1 at gmail dot com
Target Milestone: ---
compiler explorer link: https://godbolt.org/z/9oE5Ta
Note: Clang has the same bug: https://bugs.llvm.org/show_bug.cgi?id=49343
code:
#include <arm_neon.h>
// output:
// smlal v0.4s, v1.4h, v2.4h
int32x4_t good(int32x4_t acc, int16x4_t x, int16x4_t y) {
asm("smlal %[acc].4s, %[x].4h, %[y].4h"
: [acc]"=w"(acc)
: [x]"w"(x),
[y]"w"(y)
:);
return acc;
}
// output:
// smlal v0.4s, v0.4h, v1.4h
// bug: v0 is used for both x and y arguments!
int32x4_t bad(int16x4_t x, int16x4_t y, int32x4_t acc) {
asm("smlal %[acc].4s, %[x].4h, %[y].4h"
: [acc]"=w"(acc)
: [x]"w"(x),
[y]"w"(y)
:);
return acc;
}
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug inline-asm/99259] aarch64 inline asm: miscompilation depending on function parameters order
2021-02-24 19:59 [Bug inline-asm/99259] New: aarch64 inline asm: miscompilation depending on function parameters order jacob.benoit.1 at gmail dot com
@ 2021-02-24 20:01 ` jacob.benoit.1 at gmail dot com
2021-02-24 20:46 ` jakub at gcc dot gnu.org
2021-02-25 17:19 ` jacob.benoit.1 at gmail dot com
2 siblings, 0 replies; 4+ messages in thread
From: jacob.benoit.1 at gmail dot com @ 2021-02-24 20:01 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99259
Benoit Jacob <jacob.benoit.1 at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #1 from Benoit Jacob <jacob.benoit.1 at gmail dot com> ---
Sorry, as Craig mentioned on the LLVM bug, I had the wrong constraint (=w
instead of +w).
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug inline-asm/99259] aarch64 inline asm: miscompilation depending on function parameters order
2021-02-24 19:59 [Bug inline-asm/99259] New: aarch64 inline asm: miscompilation depending on function parameters order jacob.benoit.1 at gmail dot com
2021-02-24 20:01 ` [Bug inline-asm/99259] " jacob.benoit.1 at gmail dot com
@ 2021-02-24 20:46 ` jakub at gcc dot gnu.org
2021-02-25 17:19 ` jacob.benoit.1 at gmail dot com
2 siblings, 0 replies; 4+ messages in thread
From: jakub at gcc dot gnu.org @ 2021-02-24 20:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99259
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
v0 wasn't used for x and y, but for acc and x. As you said, when acc is both
input and output, you need +w or "=w" (acc) ..... "0" (acc), but even if it was
output only and couldn't clash with x or y, you'd need early-clobber - "=&w"
which would make sure that the input operands get different registers from that
output one.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug inline-asm/99259] aarch64 inline asm: miscompilation depending on function parameters order
2021-02-24 19:59 [Bug inline-asm/99259] New: aarch64 inline asm: miscompilation depending on function parameters order jacob.benoit.1 at gmail dot com
2021-02-24 20:01 ` [Bug inline-asm/99259] " jacob.benoit.1 at gmail dot com
2021-02-24 20:46 ` jakub at gcc dot gnu.org
@ 2021-02-25 17:19 ` jacob.benoit.1 at gmail dot com
2 siblings, 0 replies; 4+ messages in thread
From: jacob.benoit.1 at gmail dot com @ 2021-02-25 17:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99259
--- Comment #3 from Benoit Jacob <jacob.benoit.1 at gmail dot com> ---
Thanks for bringing up the topic of early-clobber. I had to look up some
explanation of that concept, but I found that and now I get what you're saying
- thanks!
https://stackoverflow.com/questions/15819794/when-to-use-earlyclobber-constraint-in-extended-gcc-inline-assembly
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-02-25 17:19 UTC | newest]
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2021-02-24 19:59 [Bug inline-asm/99259] New: aarch64 inline asm: miscompilation depending on function parameters order jacob.benoit.1 at gmail dot com
2021-02-24 20:01 ` [Bug inline-asm/99259] " jacob.benoit.1 at gmail dot com
2021-02-24 20:46 ` jakub at gcc dot gnu.org
2021-02-25 17:19 ` jacob.benoit.1 at gmail dot com
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