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* [Bug other/54857] New: Superfluous NOPs on Atom
@ 2012-10-08 15:44 piotr.wyderski at gmail dot com
2012-10-08 18:52 ` [Bug other/54857] " pinskia at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: piotr.wyderski at gmail dot com @ 2012-10-08 15:44 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54857
Bug #: 54857
Summary: Superfluous NOPs on Atom
Classification: Unclassified
Product: gcc
Version: 4.7.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: other
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: piotr.wyderski@gmail.com
GCC [4.7.1 on Linux and 4.6.1 on Cygwin] generates a LOT of unnecessary
NOPs when the target is Atom. The following testcase shows the odd behaviour:
int func(float f) { return (int)f; };
The output is:
gcc -S -O2 -march=atom -mtune=atom test.cpp
.LFB0:
.cfi_startproc
cvttss2si %xmm0, %eax
nop
nop
nop
nop
nop
nop
ret
.cfi_endproc
When the target is e.g. Core2:
gcc -S -O2 -march=core2 -mtune=core2 test.cpp
it is simply:
.LFB0:
.cfi_startproc
cvttss2si %xmm0, %eax
ret
.cfi_endproc
gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/mnt/local/a3d.gcc-4.7.1/libexec/gcc/x86_64-unknown-linux-gnu/4.7.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-4.7.1/configure --prefix=/mnt/local/a3d.gcc-4.7.1
--with-gmp=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites
--with-mpfr=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites
--with-mpc=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites
--with-ppl=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites
--with-cloog=/mnt/local/a3d.gcc-4.7.1/gcc-prerequisites
--with-local-prefix=/mnt/local/a3d.gcc-4.7.1 --enable-languages=c,c++
--disable-multilib
Thread model: posix
gcc version 4.7.1 (GCC)
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug other/54857] Superfluous NOPs on Atom
2012-10-08 15:44 [Bug other/54857] New: Superfluous NOPs on Atom piotr.wyderski at gmail dot com
@ 2012-10-08 18:52 ` pinskia at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu.org @ 2012-10-08 18:52 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54857
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-10-08 18:50:47 UTC ---
This was done by design for Atom see
http://gcc.gnu.org/ml/gcc-patches/2010-09/msg01104.html :
On Atom, the function return address isn't ready until 4 cycles after
function is entered.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2012-10-08 15:44 [Bug other/54857] New: Superfluous NOPs on Atom piotr.wyderski at gmail dot com
2012-10-08 18:52 ` [Bug other/54857] " pinskia at gcc dot gnu.org
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